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Intraguild predation among spiders and their effect on the pear psylla during winter
Abstract
Generalist predators may provide biocontrol service if (1) they are abundant in an agroecosystem, (2) intraguild predation is low, (3) alternative prey is scarce, and (4) pest population increase is slow. These conditions are met in fruit orchards during winter and in early spring. Spiders of the genera Anyphaena and Philodromus remain active during winter and prey on pests, including overwintering Cacopsylla pyri. As these spiders belong to the same guild they can also disrupt their biocontrol potential via intraguild predation. Hence, we aimed here to assess predation frequency on Cacopsylla and among these spiders over the course of two winters. We investigated the width of the trophic niche and prey preference of the two winter-active spider species. We developed specific primers and investigated the actual predation by means of molecular methods (DNA detection of prey in the gut of spider predators). From a dozen of potential prey types (11 arthropod orders) offered in the laboratory, both Anyphaena and Philodromus accepted the majority of them. The trophic niches of both species were thus wide and the overlap was considerable. Both Anyphaena and Philodromus preferred Cacopsylla to spiders. In the field, the frequency of Anyphaena individuals which fed on Cacopsylla was very high both at the beginning and at the end of winter. The frequency of Anyphaena individuals which fed on Philodromus was low throughout the two studied winters. The ambient temperature did not affect the frequency of which fed on the pest. Over the two winters, Anyphaena captured Cacopsylla significantly more often than Philodromus. Our results show that winter-active spiders accepted the pear psylla frequently and that intraguild predation was much lower than predation on the pest. Thus winter-active spiders have potential to be used as biocontrol agents.
... Recent field and laboratory studies indicate that these winter-active spider genera could suppress pest populations during the winter and early spring period (Gajski & Pekár, 2021;Michalko et al. 2017;Petráková et al. 2016;Pekár et al. 2015). Yet, the overall natural diet of winteractive spiders during the winter period, as well as factors that may influence it (such as management type) have not been investigated. ...
... Our findings partially agree with results from previous laboratory studies, which demonstrated that the predation activity of Anyphaena was higher across the range of all winter temperatures compared to the activity of Philodromus and Clubiona Michálek et al. 2022). However, our results on proportion of prey-positive individuals contradict results from PCR prey-detection studies that were also performed on Anyphaena and Philodromus spiders sampled during winter Petráková et al. 2016). In these studies, the proportion of prey-positive Fig. 5 Comparison of prey preference (i.e., a difference between expected and observed consumption) of winter-active spiders (genera Anyphaena, Clubiona, and Philodromus pooled) for eight to nine prey types collected under two managements types and from two periods. ...
... Due to the amplification of only a single sequence, PCR diagnostics with specific primers can achieve a higher number of positive results compared to those acquired using universal primers in metabarcoding studies, which are more dependent on the amount of prey-DNA. Nevertheless, both the previous PCR diagnostic studies Petráková et al. 2016) and our metabarcoding study suggest that the winter-active spiders naturally preyed more frequently on pests than on alternative prey, which will be discussed further in detail (see the section Prey prevalence and prey preference). ...
Modern agricultural pest management systems rely on naturally occurring generalist predators to promote pest suppression. Still, little research has been done to assess their overall effectiveness, especially over the winter period when their potential is high. In this study, we focused on three genera of winter-active spiders Clubiona, Philodromus, and Anyphaena, common predators on pear trees in Central Europe during winter and early spring. We investigated their predation activity, natural diet, and prey preference using molecular gut content and abundance data obtained from cardboard bands, which served as natural shelters. We compared these characteristics between two distinct biocontrol-promoting managements—integrated pest management (IPM) and organic management (ORG). We found the proportion of prey-positive spider individuals during the winter period to be lower compared to the spring period with Anyphaena having by far the highest proportion. The prey composition during winter was more diverse in ORG orchards, but in both managements, it was inclined toward pests, mostly pear psyllids. Conversely, in early spring, despite psyllids still being a part of the diet, spiders in IPM orchards preyed more frequently on neutral prey (mostly dipterans), while the spiders from organic orchards preyed mostly on pests (lepidopterans). Although more data are needed to assess trophic interactions and the overall efficiency of these winter-active predators in complex arthropod food webs present in pear orchards, the results obtained from this research provide the first evidence of higher pest predation during a period of agricultural quiescence.
... Winter in the temperate zone is often considered to be a period of quiescence for arthropods resulting in the limited dynamics of terrestrial arthropod food-webs. However, some arthropods remain active even during winter and interact in simplified food-webs through predatorprey and intraguild interactions (Birkhofer et al., 2010;Eitzinger and Traugott, 2011;Petrakova et al., 2016). As predator-prey and intraguild interactions in winter may determine the population dynamics of both pests and natural enemies at the onset of the growing season (Athey et al., 2016), interactions during winter are important especially for conservation biological control Lefebvre et al., 2017). ...
... For example, predation by winter-active spiders on psylla, one of the most serious pests in pear orchards in Central Europe, increases with increasing psylla densities during spring (Gajski and Pekár, 2021) and such spiders significantly reduce psylla densities during the non-growing season . Nevertheless, winter-active spiders also include a large proportion of alternative collembolan prey in their diet and intraguild spider prey (Petrakova et al., 2016;Michalko et al., 2021a). This strong predation on intraguild and alternative prey by winter-active spiders may potentially compromise their biocontrol function later in the growing season, when various pests start to invade the agroecosystem (Symondson et al., 2002;Mezőfi et al., 2020;Hambäck et al., 2021). ...
... mat. 1) and winter-inactive insect predators (predaceous Heteroptera and Coleoptera, Neuroptera, ants, and parasitoid Hymenoptera). We distinguished between winterinactive spiders and insect predators because winter-active spiders prefer spiders over insect predators as intraguild prey Petrakova et al., 2016;Mezőfi et al., 2020;Hambäck et al., 2021). We did not include earwigs in the analyses because their role in fruit orchards is ambiguous; i.e., they are omnivores predating on pests (Niedobova et al., 2021), but can also cause substantial damage in fruit orchards (Kahl et al., 2021;Quarrell et al., 2021). ...
Although winter in the temperate zone is considered to be the period of arthropod quiescence, some pests and their natural enemies remain active and interact in simplified food-webs. Limited information exists about the relative importance of top-down and bottom-up processes regulating arthropod food-webs and their spatio-temporal dynamics during winter. This information is essential for the development of effective conservation biocontrol methods. We investigated how the pest management of pear orchards (integrated [IPM] vs organic) and tree location within orchards (margin vs centre) influence the association between densities of winter-active spiders, insect herbivores and winter-inactive predators (spiders, insects) from October to April. We installed carboard bands on trunks and branches of pear trees in four organic and four IPM orchards to collect bark-dwelling arthropods. We then modelled relationships between the densities of four functional arthropod groups, namely winter-active spiders, winter-inactive spiders, winter-inactive insect predators, and herbivores. In early winter, we found a hump-shaped relationship between the densities of winter-active spiders and herbivores. This agrees with the top-down model of the ecosystem exploitation hypothesis, predicting that predators are first bottom-up limited, then accumulate with prey densities, and exert top-down control when they become sufficiently abundant. The densities of herbivores strongly declined during winter, a phenomenon which may be partly, along with other causes of natural mortality, attributable to predation by winter active spiders. The association between winter-active spiders and winter-inactive arthropod predators switched from positive to none in organic orchards or even to a negative association in IPM orchards. Negative intraguild interactions seem to be intensified due to the declining availability of alternative prey. Overall, the investigated food-webs seem to be mostly top-down regulated during winter, and IPM seems to intensify intraguild interactions.
... The experimental results support that the intraguild predation may be used as biological control of pest species. According to Petráková et al, 1 generalist predators may provide biocontrol service if they are abound in an agroecosystem, the intraguild predation is low, the alternative resources are scarce, and the increase of pest population is slow. These conditions are met in fruit orchards during winter and in early spring. ...
... then p is an equilibrium point of the differential system (1) . ...
... By (12), the first Lyapunov coefficient, 1 According to (11), we have that the derivative of the real part of the complex eigenvalues respect to c 3 is ...
The conditions to have a stable limit set in the positive octant for an intraguild predation model are given, considering a general family of functional responses for the predators and a wide range of growth rate functions for the prey. The limit sets are obtained by Hopf or Bautin bifurcation. The results obtained in previous works about intraguild predation models, which consider logistic growth rate for the prey and Holling functional responses, are generalized.
... The prey utilization of a generalist predator can vary seasonally (Whitney et al., 2018), but is usually investigated only during the growing season (e.g., Chapman et al., 2013;Szendrei et al., 2014;Roubinet et al., 2017Roubinet et al., , 2018Staudacher et al., 2018;Mezőfi et al., 2020;Saksongmuang et al., 2020). Prey utilization patterns during the non-growing season, when generalist predators can exert a strong biocontrol effect (Birkhofer et al., 2008;Pekár et al., 2015;Athey et al., 2016), have been studied only rarely (Eitzinger and Traugott, 2011;Petráková et al., 2016). ...
... In the temperate zone, most arboreal arthropods hibernate in the soil, litter, or dense ground vegetation (Kirchner, 1987;Alford, 1999;Boinot et al., 2019) and only a few, such as springtails, psyllids, and spiders, remain active in trees where they interact in highly simplified food-webs Petráková et al., 2016;. Philodromid spiders, such as Philodromus cespitum (Walckenaer, 1802), are among the most important generalist natural enemies of psyllid pests in pear orchards . ...
... For this study, we used spiders collected during winter and spring in two consecutive years (December 2012 -April 2014) in the same pear orchard as the individuals for the laboratory experiments. There are five Philodromus species in the pear orchard (hereafter shortened to Philodromus spp.), namely P. cespitum (85% relative abundance), P. praedatus (3%), P. buchari (3%), P. aureolus (3%), and P. albidus (6%) Petráková et al., 2016;. However, differences in prey preference among Philodromus spp. ...
Populations of generalist predators are often comprised of a mixture of specialist and generalist individuals and this intraspecific variation in prey utilization may affect pest suppression. However, little is known about seasonal changes in prey utilization by generalist predators, especially during winter, when some generalist predators exert strong biocontrol effects. We used prey preference experiments on Philodromus cespitum (Araneae: Philodromidae) and molecular gut-content analyses of Philodromus spp. (dominated 85% by P. cespitum) to study the dynamics of spider specialization in a pear orchard during the non-growing season. In the laboratory, P. cespitum preferred springtails (Collembola) over the pear psylla, Cacopsylla pyri, an important pest of pear. The presence of springtails in guts of Philodromus spp. did not affect detection of psylla by molecular gut-content analysis in specimens collected from the pear orchard. The philodromid population comprised of a mixture of specialists and generalists in winter, but was composed mainly of generalists in spring. Greater variation in prey utilization during winter most likely reflects a patchy distribution of prey and philodromids switching to a less active hunting mode. Seasonal specialization of individual generalist predators could be the result of their ability to change hunting mode in response to changing environmental conditions and prey distribution. Our study demonstrates that alternative (collembolan) prey are unlikely to affect philodromid predation on psyllids and suggests that changes occur in the spatial structure of predator-pest interactions from winter to spring.
... Spiders are not able to distinguish between all prey species prior to attack. For example, cursorial Philodromus spiders distinguished between a psylla pest and Dictyna spiders before they initiated an attack (Petráková et al. 2016). However, cursorial Pardosa spiders needed to taste aphids to distinguish between toxic and palatable aphid species (Toft and Wise 1999a). ...
... Furthermore, generalist spider species lack specialized adaptations to overcome IG prey (Pekár and Toft 2015). Other spiders, therefore, represent a low-rank diet item for generalist spiders and the intensity of IGP decreases with the availability of alternative innocuous and palatable prey (Rickers et al. 2006;Oelbermann et al. 2008;Michalko and Pekár 2015;Petráková et al. 2016). However, if the top predator-to-mesopredator body size ratio is sufficiently large, then IGP increases rapidly and small spiders can become more preferable prey for large spiders than pests (Petcharad et al. 2018). ...
... For example, various spider species are adapted to catch pests at different temperatures. Two syntopic cursorial spider species, Anyphaena accentuata (Walckenaer) (Anyphaenidae) and Philodromus cespitum (Walckenaer), which occupy a similar trophic niche, differ in their prey capture efficiency at various temperatures Petráková et al. 2016). Anyphaena is more efficient in capturing fruit flies at 15 °C while Philodromus is more efficient at temperatures above 20 °C . ...
The role of generalist predators in biological control remains controversial as they may not only reduce pest populations but also disrupt biocontrol exerted by other natural enemies. Here, we focus on spiders as a model group of generalist predators. They are among the most abundant and most diverse natural enemies in agroecosystems. We review their functional traits that influence food-web dynamics and pest suppression at organisational levels ranging from individuals to communities. At the individual and population levels, we focus on hunting strategy, body size, life stage, nutritional target, and personality (i.e., consistent inter-individual differences in behaviour). These functional traits determine the spider trophic niches. We also focus on the functional and numerical response to pest densities and on non-consumptive effects of spiders on pests. At the community level, we review multiple-predator effects and effect of alternative prey on pest suppression. Evidence for a key role of spiders in pest suppression is accumulating. Importantly, recent research has highlighted widespread non-consumptive effects and complex intraguild interactions of spiders. A better understanding of these effects is needed to optimize biocontrol services by spiders in agroecosystems.
... The PCR conditions were as follows: initial denaturation at 94 ∘ C for 3.5 min; 40 cycles of 94 ∘ C for 1 min, 49 ∘ C for 1 min (annealing temperature), 72 ∘ C for 1.5 min; and a final extension at 72 ∘ C for 7 min. Palpimanus spiders were screened for the presence of Philodromus spiders using Phi28F (5́-TTGTCGCACCGCCTCGC) and Phi28R (5́-CACGCGAGAAGCRCGCCTTC) primers (Petráková et al., 2016). The PCR conditions were as follows: initial denaturation at 95 ∘ C for 3 min; 38 cycles of 95 ∘ C for 45 s, 54 ∘ C for 45 s, 72 ∘ C for 1 min; and a final extension at 72 ∘ C for 7 min. ...
... A failure to detect any difference could be because we measured the detection time only using qualitative indicators, not quantitative ones. By measuring prey DNA concentration in the gut, we might increase the chance of finding differences (Petráková et al., 2016). However, there was a large difference between the two pairs. ...
... This value is much longer than those reported by other authors for spiders (e.g. Agustí et al., 2003;Kuusk et al., 2008;Kerzicnik et al., 2012;Chapman et al., 2013;Petráková et al., 2016). Why might this be so? ...
1. Feeding behaviour of generalist and specialist predators is determined by a variety of trophic adaptations. Specialised prey‐capture adaptations allow specialists to catch relatively large prey on a regular basis. As a result, specialists might be adapted to exploit each item of prey more thoroughly than do generalists.
2. It was expected that obligatory specialist cursorial spiders would feed less frequently than generalists but for a longer time and, thus, that their foraging pause would be longer. First, the feeding frequencies of three generalist spider species (Cybaeodamus taim, Harpactea hombergi, Hersiliola sternbergsi) were compared with those three phylogenetically related specialist species: myrmecophagous Zodarion rubidum, and araneophagous Nops aff. variabilis and Palpimanus orientalis.
3. Generalists captured more prey, exploited each item of prey for a significantly shorter time, and had a shorter foraging pause than was the case for specialists. Generalists also gained significantly less relative amount of prey mass than did specialists.
4. Second, the study compared the prey DNA degradation rate in the gut of generalists and specialists by means of PCR. The degradation rate was not significantly different between specialists and generalists: the detectability half‐life was estimated to exist for 14.3 days after feeding.
5. This study shows that the feeding strategies of cursorial generalist and obligatory specialist spiders are different. Obligatory specialists have evolved a feeding strategy that is based on thorough exploitation of a few large prey, whereas generalists have evolved a strategy that is based on short exploitation of multiple small items of prey.
... The effective predation of pests by predators in winter is predicated upon minimal disturbance during harvest, sedentary and easily accessible pests, low availability of alternative prey and a dearth of other natural enemies (Pekár et al., 2015). Alternative prey are often scarce in winter, sometimes directing predators towards pests (Petráková et al., 2016), but otherwise towards fellow predators. ...
... Although not always significant (Petráková et al., 2016), intraguild predation may be a profound problem arising from winter predator activity if alternative prey are not adequately available (Davey et al., 2013), although alternative prey provision is not a panacea and habitat complexity may be more important (Korenko & Pekár, 2010). Increasing habitat complexity, even artificially, can mitigate the impacts of intraguild predation to some degree (Michalko et al., 2017). ...
Conservation biocontrol, the regulation of crop pests by naturally occurring biocontrol agents (e.g., predators and parasitoids), is predominantly monitored throughout periods of primary crop growth when pests exert the most observable impact on yields. Pest‐focused agricultural biomonitoring often overlooks post‐harvest, winter and even early‐season biocontrol, despite the significant predator–pest interactions during these periods that profoundly affect pest abundance and, consequently, crop yields. Rapid advances in biomonitoring, particularly in the detection of predator–pest interactions that underpin biocontrol, provide an opportunity to reconsider how and when we monitor these interactions.
Advances in agricultural biomonitoring must transcend methodological innovation and encompass conceptual changes in the monitoring of agricultural systems. Here, we assess existing evidence supporting the importance of periods beyond primary crop growth for biocontrol and how predator–pest interactions are likely to evolve during these periods, subsequently influencing pest population dynamics during the primary crop growth period.
We advocate for a greater concerted effort to establish continuous monitoring of biocontrol interactions, particularly beyond primary crop growth periods in temperate climates. To facilitate this, we also summarise the methodological approaches that can make it possible and explore how extending sampling across the full annual cycle might impact the practicalities and outcomes of these approaches.
Year‐round monitoring of biocontrol interactions, both in crops and adjacent semi‐natural habitats, will provide a previously intractable understanding of predator–pest dynamics, offering significant potential to enhance our ability to optimise and manipulate these systems. This would manifest in reduced crop yield losses, pest infestation rates and disease transmission, with concomitant long‐term financial, environmental and land‐use benefits.
... During the winter they are present on the bark of trees, where they actively hunt prey. Recent studies have shown their potential in controlling pest populations during the winter period, especially pear psyllidsthe major insect pest in pear orchards (Pekár et al., 2015;Petráková et al., 2016). ...
... Our former studies focused mainly on spiders of the genera Anyphaena and Philodromus, which frequently occur in orchards in Central Europe. Predation activity during the winter and the effect of intra-guild predation on pest suppression has been thoroughly investigated in these genera (e.g., Pekár et al., 2015;Petráková et al., 2016). ...
Winter-active arthropod predators (like vegetation-dwelling spiders) significantly suppress pest populations during winter in pome fruit orchards in Central Europe. Clubiona spiders are very abundant in orchards and have been observed to be active during winter. Here, we performed laboratory experiments to assess the movement and predation activity of clubionids at low temperatures. In addition, we also assessed prey survival (psyllids and crickets). We revealed that Clubiona spiders actively moved even at a temperature below 0 °C. Pest prey (Cacopsylla sp.) was able to survive at low temperatures, but crickets died at 3 and -1 °C. Overall Clubiona activity was very low but present during the whole observation period of five days. The predation activity of Clubiona declined with lower temperatures for both cricket and pest (Cacopsylla sp.) prey. Nevertheless, 44% and 25% of Clubiona individuals captured and consumed psyllid and cricket prey, respectively, even at the lowest temperature of −1 °C. Our results show that Clubiona spiders are active predators at low temperatures and, therefore, should contribute to the suppression of overwintering pest populations.
... Recent work has demonstrated that Philodromus spp. are effective at suppressing woolly apple aphid (Mezofi et al. 2020) and pear psylla , Petráková et al. 2016. Philodromus spp. ...
... are thought to be particularly good biological control agents because, unlike other spiders, they primarily prey on pest species . They are also winter active, which allows them to consume overwintering pear psylla and decrease their populations , Petráková et al. 2016. ...
Spiders are key predators in many agroecosystems, including orchards. Despite the importance of spiders in biological control, pesticide nontarget effects on this group are poorly described. This is especially true for herbicides, which spiders frequently encounter as they move between the ground cover and tree canopy. We sought to determine the nontarget effects of seven herbicides used in orchards on three species of spiders that are commonly found in Washington state (USA) orchards: Pelegrina aeneola (Curtis) (Araneae: Salticidae), Philodromus cespitum (Walckenaer) (Araneae: Philodromidae), and Phanias watonus (Chamberlin & Ivie) (Araneae: Salticidae). Immature spiders were collected from orchards and used in laboratory assays. Single spiders were placed in vials with dried herbicide residues and mortality was evaluated after 1, 2, and 5 d. We also evaluated herbicide impacts on prey consumption rates and on spider movement using motion-tracking software. Only oxyfluorfen caused significant spider mortality. P. cespitum seemed to be less acutely sensitive to oxyfluorfen than the two salticid species. Several herbicide treatments significantly increased locomotion in P. cespitum, whereas rimsulfuron numerically decreased movement of P. aeneola. Sulfonylurea herbicides (rimsulfuron, halosulfuron) decreased prey consumption of P. aeneola. Our work indicates that although spiders may be less acutely sensitive to some pesticides than beneficial insects, they can be affected by sublethal effects of herbicides. Future work should determine if herbicide applications impact spider abundance in the field and reduce biological control services. In general, more work is needed on the impacts of herbicides on natural enemies.
... However, honeydew-collecting ants can benefit psyllid parasitoids such as P. mitratus as they provide protection from hyperparasitoids 71 . Examples of IGP in pear orchards have also been reported among ladybug species 76 and among spider species 77 . Even if IGP occurs, the outcomes could still benefit pest control when pest population increase is slow and intraguild predation is low 77 , which is the case in early spring in pear orchards. ...
... Examples of IGP in pear orchards have also been reported among ladybug species 76 and among spider species 77 . Even if IGP occurs, the outcomes could still benefit pest control when pest population increase is slow and intraguild predation is low 77 , which is the case in early spring in pear orchards. A careful assessment of the impacts of IGP and IGC on biocontrol in pear orchards, given potential differences during the pre-bloom and the bloom seasons, should be considered in the development of IPM strategies against pear psyllids. ...
Pear cultivation accounts for a large proportion of worldwide orchards, but its sustainability is controversial because it relies on intensive use of pesticides. It is therefore crucial and timely to find alternative methods to chemical control in pear orchards. The psyllids Cacopsylla pyri and Cacopsylla pyricola are the most important pests of pear trees in Europe and North America, respectively, because they infest all commercial varieties, causing damage directly through sap consumption or indirectly through the spread of diseases. A set of natural enemies exists, ranging from generalist predators to specialist parasitoids. Trechnites insidiosus (Crawford) is undoubtedly the most abundant specialist parasitoid of psyllids. In our literature review, we highlight the potential of this encyrtid species as a biological control agent of psyllid pests by first reviewing its biology and ecology, and then considering its potential at regulating psyllids. We show that the parasitoid can express fairly high parasitism rates in orchards, and almost perfectly matches the phenology of its host and is present early in the host infestation season, which is an advantage for controlling immature stages of psyllids. We propose new research directions and innovative approaches that would improve the use of T. insidiosus in integrated pest management strategies in the future, regarding both augmentative and conservation biocontrol. We conclude that T. insidiosus has many advantages and should be included as part of integrated biological control strategies of pear psyllids, along with predators, in‐field habitat conservation, and the rational use of compatible chemicals. © 2021 Society of Chemical Industry.
... 32 The PCR was performed using specific primers designed to detect Cacopsylla mitochondrial cytochrome oxidase I (COI) gene fragments of 238 bp size. We used a primer set consisting of a forward primer (Cp3F: 5'-GTCTAGTAGAC-CAAGGAG-TAGG) designed by Agustí et al., 33 and a reverse primer (CP6Rnew: 5'AACAR-RAAAGCTGTAATTARTACTG) designed by Petrákova et al. 34 The primer set was PCR-tested on all three Cacopsylla species found at the study site (C. pyri L., C. pyricola Foerster and C. pyrisuga Foerster). ...
... 55,62 However, as there was a high diversity of spider species in the studied orchard, it is likely that larger individuals prey on smaller ones, such as theridiids. 34,63,64 Yet, smaller spiders preyed on psyllids less frequently than larger spiders; thus, the bias from secondary predation should be negligible. ...
BACKGROUND
Modern pest control management systems are based on the support of naturally occurring arthropod predators, as it has been shown that such predators offer an important ecosystem service. However, most naturally occurring arthropod predators are generalists (euryphagous). Their role in the biological control of specific pests has been recognized but remains poorly studied. Here, we focused on the naturally occurring arthropod predators of psyllids – the main insect pest of pear trees. We investigated the abundance of psyllids and all of their potential enemies in an abandoned pear orchard on a weekly basis from early spring to early summer. In addition, employing polymerase chain reaction diagnostics and specific primers, we investigated the predation rate on psyllids in all predators collected.
RESULTS
We found four predatory groups: spiders were the most abundant (60%, N = 756), followed by coccinellid beetles, anthocorid bugs and cantharid beetles. Anthocorids and spiders had the highest predation rates among the predatory groups. Among spiders, >50% of foliage‐dwelling spiders (belonging to the genera Philodromus and Clubiona; N = 206) were positive for psyllids and showed a numerical response to the abundance of psyllids.
CONCLUSION
We conclude that foliage‐dwelling spiders are, of the four groups, the most important natural enemies of psyllids on pear trees during spring in Central Europe, as they outnumber specialized Anthocoris bugs. © 2021 Society of Chemical Industry
... This genus has also been cited among the most abundant in the canopy of fruit orchards in other areas of Europe [34,46,[48][49][50], including pear trees [3,31,51]. Philodromids have been reported to be active in pear orchards throughout the year, lowering the population growth of C. pyri in its initial phases [51][52][53]. The second most abundant family in our study was Oxyopidae, which is also very abundant in agricultural crops [54], including pome fruit orchards [4]. ...
... Philodromus spp. has been reported to use psyllids as a major source of prey during winter, and as one of the key predators to reduce the psyllid populations during this period in pear orchards [51][52][53]. Therefore, the reduction of the overwintering population of philodromids could translate into higher psyllid outbreaks in spring. ...
Simple Summary
Spiders are one of the most abundant predatory arthropods in fruit tree orchards, where they contribute to pest control. The application of pesticides in these orchards has been largely reported to negatively affect spiders, lowering their abundance and diversity. In this study, we described the structure of the community of spiders in four Mediterranean pear orchards, and we assessed the effect of the intensity of spraying on the spider assemblages. Two of the orchards had low-intensity spraying of pesticides and the other two were sprayed more intensively. Spiders were generally more abundant and diverse in the orchards with low intensity of spraying. Moreover, the impact of the intensity of spraying varied depending on the family of spiders, with only some families of wandering spiders being significantly affected by the intensity of spraying. This suggests that the impact of pesticides on spider could be explained, at least in part, by their foraging mode. However, other local environmental factors apart from the intensity of spraying may have accounted for the differences in abundance and structure of the spider assemblages registered in pear orchards in the present research.
Abstract
Spiders are key predatory arthropods that are negatively affected by spraying pesticides in orchards. The aim of this research was to determine the structure of the community of spiders in pear orchards and the impact of the intensity of spraying. The study was carried out over three years in four pear orchards in southern Spain; two of them were conducted by ourselves with no or low-intensity spraying of insecticides, and two under the criteria of technicians (conventional). Spiders were sampled on pear trees by the beating method. The orchards hosted a rich community of spiders belonging to 13 different families and 51 genera. However, the genera Philodromus, Oxyopes, Cheiracanthium, Icius, and Neoscona accounted for 72% of the captures. Spiders were more abundant and had a higher richness of genera in the low-intensity spraying than in conventional orchards. Philodromidae, Salticidae, and Cheiracanthiidae experienced a significant population reduction in conventional orchards, while Araneidae, Linyphiidae, and Thomisidae were not significantly affected by the intensity of spraying. The wandering hunting mode could explain the negative impact on Philodromidae, Salticidae, and Cheiracanthiidae but does not explain the lack of effect on Oxyopidae and Thomisidae. No significant effect was found on any family of web builders.
... Although these generalist predators can effectively reduce pest numbers (Symondson, Sunderland & Greenstone, 2002;Nyffeler & Sunderland, 2003), many factors can influence their role in pest suppression and food-web dynamics at both community and individual levels . Several environmental factors and functional traits can be directly or indirectly involved, including the presence or absence of alternative prey (Madsen, Terkildsen & Toft, 2004;Kuusk & Ekbom, 2010), the intensity of intraguild predation or predator interference (Snyder & Wise, 1999;Wise, 2006;Petráková et al., 2016;Michalko et al., 2017), the season of the year (Snyder & Wise, 2001), hunting strategy or guild (Schmitz, 2008;Miller, Ament & Schmitz, 2014;Liu et al., 2015;, or ontogenetic differences (Bartos, 2011). ...
... In addition, Ph. cespitum also feeds on other pests (Klein, 1988;Wisniewska & Prokopy, 1997;Ghavami, 2008;Michalko et al., 2017). This spider remains active during winter when other predators are dormant, and consequently, it can also reduce, for example, overwintering psyllid populations Petráková et al., 2016). Ph. cespitum is among the most abundant hunting spiders in the canopy of apple orchards both in Europe Pekár, 1999;Pekár & Kocourek, 2004;Markó et al., 2009) and North America (Miliczky, Horton & Calkins, 2008;Sackett, Buddle & Vincent, 2008), and in our study it consumed the second-highest number of pests (following Clubiona spp.), compared to the number of natural enemies it consumed ( Fig. 5; Table S6). ...
Spiders (Araneae) form abundant and diverse assemblages in agroecosystems such as fruit orchards, and thus might have an important role as natural enemies of orchard pests. Although spiders are polyphagous and opportunistic predators in general, limited information exists on their natural prey at both species and community levels. Thus, the aim of this study was to assess the natural prey (realized trophic niche) of arboreal hunting spiders, their role in trophic webs and their biological control potential with direct observation of predation events in apple orchards. Hunting spiders with prey in their chelicerae were collected in the canopy of apple trees in organic apple orchards in Hungary during the growing seasons between 2013 and 2019 and both spiders and their prey were identified and measured. Among others, the composition of the actual (captured by spiders) and the potential (available in the canopy) prey was compared, trophic niche and food web metrics were calculated, and some morphological, dimensional data of the spider-prey pairs were analyzed. Species-specific differences in prey composition or pest control ability were also discussed. By analyzing a total of 878 prey items captured by spiders, we concluded that arboreal hunting spiders forage selectively and consume a large number of apple pests; however, spiders’ beneficial effects are greatly reduced by their high levels of intraguild predation and by a propensity to switch from pests to alternative prey. In this study, arboreal hunting spiders showed negative selectivity for pests, no selectivity for natural enemies and positive selectivity for neutral species. In the trophic web, the dominant hunting spider taxa/groups ( Carrhotus xanthogramma , Philodromus cespitum , Clubiona spp., Ebrechtella tricuspidata , Xysticus spp. and ‘Other salticids’) exhibit different levels of predation on different prey groups and the trophic web’s structure changes depending on the time of year. Hunting spiders show a high functional redundancy in their predation, but contrary to their polyphagous nature, the examined spider taxa showed differences in their natural diet, exhibited a certain degree of prey specialization and selected prey by size and taxonomic identity. Guilds (such as stalkers, ambushers and foliage runners) did not consistently predict either prey composition or predation selectivity of arboreal hunting spider species. From the economic standpoint, Ph. cespitum and Clubiona spp. were found to be the most effective natural enemies of apple pests, especially of aphids. Finally, the trophic niche width of C. xanthogramma and Ph. cespitum increased during ontogeny, resulting in a shift in their predation. These results demonstrate how specific generalist predators can differ from each other in aspects of their predation ecology even within a relatively narrow taxonomic group.
... Generalist spider species lack specialized adaptations to overcome intraguild prey (Pekár and Toft, 2015), and other spiders could represent a low-ranking dietary item for these generalists. The intensity of IGP tends to decrease when alternative innocuous and more palatable prey are available (Michalko and Pekár, 2015;Petráková et al., 2016). ...
Spiders may play a crucial role as versatile predators within agroecosystems. Their diverse behavioral patterns, organized into different guilds, can significantly impact multitrophic interactions. Natural vegetation cover surrounding orchards can influence this predatory behavior, which in turn can impact the feeding patterns of different spider predatory guilds. This study aims to examine the differences among spider guilds actively foraging on apple orchards with different levels of surrounding natural vegetation density (SNVD). To achieve this, natural carbon and nitrogen isotope enrichment was used to assess the variations in isotopic signatures among spider guilds across a gradient of surrounding natural vegetation cover, categorized into three levels (low, medium, and high density), as an indicator of landscape complexity. The mean carbon and nitrogen isotopic signatures exhibited greater variability in diurnal aerial ambushers and orb-weaving spiders, particularly in landscapes with high complexity. Interestingly, similar variability was observed in samples from orchards surrounded primarily by agricultural land (with low SNVD). No significant differences in spider abundance were found across guilds or SNVD categories in apple orchards, suggesting that the spiders guilds identified in these orchards are not influenced by landscape categories. We further describe the guilds identified, which could potentially contribute to the biological control of pests in apple orchards.
... Although F. auricularia is not commonly reared for mass release, enhancing earwig populations by providing refugia is recommended (Shaw et al. 2021). Other C. pyri natural enemies include ladybird adults and larvae (Coccinellidae) (Fountain et al. 2013;Prodanović et al. 2010), lacewing larvae (Neuroptera) (DuPont and Strohm 2020;DuPont et al. 2023), spiders (Araneae) (Petrakova et al. 2016), other anthocorid species (Sigsgaard 2010;Vrancken et al. 2014) and parasitoids (Prodanović et al. 2010;Tougeron et al. 2021). ...
Pear psyllid (Cacopsylla pyri) is the dominant pest of UK pear orchards, with an estimated cost of £5 million per annum. Insecticide withdrawal and increased pesticide resistance of C. pyri have led many growers to depend more on natural enemies for pest management, including earwigs. However, there is concern how phenological events may shift with future climate change, which may result in phenological mismatches. This study aimed to determine shifts in timing of phenological events within an agroecosystem and predict phenological mismatches or synchronies between trophic levels. We evaluated three models: the C. pyri phenology model, the earwig degree day model and the PhenoFlex model (flowering time). Phenological events predicted by models included: first, full and last flowering time for Pyrus communis; peak psyllid abundance date for first-generation (G1) C. pyri nymphs and second-generation (G2) eggs, nymphs and adults; and peak abundance date for stage 4 Forficula auricularia and adults. Findings indicated that the timing of phenological events was advancing for all trophic levels, becoming significantly earlier under the current time period. Furthermore, predictions indicated that timing events would continue to advance under the RCP8.5 scenario. However, not all phenological events advanced at the same rate; the date of peak C. pyri G1 nymph abundance advanced at a higher rate than full flowering time, which could result in a phenological mismatch by 2071. Conversely, C. pyri and F. auricularia showed phenological synchrony, with peak abundance dates advancing at a similar rate, which could be beneficial for future biological control.
... It is recognized for its complexity in disrupting traditional trophic hierarchies and influencing the dynamics of food webs and ecological communities (Polis et al., 1989;Holt & Polis, 1997;Arim & Marquet, 2004;Wang et al., 2019;Parimuchova et al., 2021). This intricate form of interaction is particularly evident among arachnids, which are known for their diverse predatory strategies and behavioral adaptations (Rypstra & Samu, 2005;Punzo, 2007;Houser et al., 2014;Petráková et al., 2016;Wise et al., 2023). ...
Intraguild predation, in which animals within the same guild prey on each other, is quite common among arachnids, especially dwelling on the ground. While pseudoscorpions can be found on the ground, tree trunks, and canopies, there is limited evidence of predation among pseudoscorpion species in their natural habitats. This study reports predatory interactions among four species of bark-dwelling pseudoscorpions in the Brazilian Cerrado. We observed two species of Victorwithius (Withiidae) (V. similis and V. rufus) opportunistically attacking and feeding on nymphs of Paratemnoides nidificator (Atemnidae). Additionally, Parachernes melanopygus (Chernetidae) acted as a social parasite, feeding on juveniles within colonies. These observations were made in six different regions of the Brazilian Cerrado. In all cases, P. nidificator was placed as the intraguild prey, while the other species acted as intraguild predators. In this system, Paratemnoides colonies may represent a predictable food resource for other pseudoscorpions, especially during the dry season when prey is scarce.
... Understanding overwintering ecology is important not only for the survival of a spider's local population but also for the health of agroecosystems in the following season, as the number of surviving winter spiders can serve as important biocontrol agents for pest pressure. Some winter studies regarding overwintering spiders have documented a number of important features, such as energy balance and metabolic changes [2], body size and survival [3], the tradeoff between increased mortality and growth [4], intraguild predation [5], protection strategy [6], and predation activity [7] in winter. Microbial communities may significantly influence the varied lifestyles of insect hosts [8] and can enhance the cold tolerance and survival of host arthropods under cold conditions [9]. ...
Simple Summary
There are differences in the cold resistance and anti-freeze compound levels in the two sexes of Pardosa astrigera, driving us to explore the differences in their intestinal microbiome. In this study, intestinal bacterial communities of P. astrigera in winter were compared using 16S rRNA high-throughput sequencing. The results showed significant differences in most alpha diversity indices and the relative abundances of dominant bacteria between males and females. Our research reveals the significant role of sex in shaping the diversity and composition of intestinal bacteria in overwintering P. astrigera. We suggest that Pseudomonas versuta (belonging to Proteobacteria) and Rhodococcus erythropolis (belonging to Actinobacteriota) may have the potential to play key roles in overwintering P. astrigera.
Abstract
Gut microbiota can promote the resistance of host arthropods to low-temperature stress. Female Pardosa astrigera have a lower anti-freeze compound level and weaker resistance to cold temperatures than the males in winter, which implies that their intestinal bacteria may be different during overwintering. This study primarily compared the intestinal bacterial communities between the two sexes of P. astrigera in a temperate region using 16S rRNA gene sequencing. Our findings indicated that the Chao1 and Shannon indices of intestinal bacteria in females were significantly higher than those in males, while the Simpson index in females was significantly lower than that in males. The male intestinal bacterial community was characterized by Proteobacteria and Actinobacteriota at the phylum level and by Pseudomonas and Rhodococcus at the genus level, with total relative abundances of 89.58% and 85.22%, respectively, which were also significantly higher than those in females, whose total relative abundances were 47.49% and 43.68%, respectively. In contrast, the total relative abundances of Bacteroidota and Firmicutes were significantly lower in males (4.26% and 4.75%, respectively) than in females (26.25% and 22.31%, respectively). Noteworthy divergences in bacterial communities were also found through an LEfSe analysis between females and males. Additionally, the results of the PICRUSt2 analysis showed that six out of eleven level-2 pathways related to key metabolic functions were significantly (or marginally significantly) higher in females than males, and five other level-2 pathways were significantly (or marginally significantly) lower in females than males. Our results imply that significant gender differences exist in intestinal bacterial communities of overwintering P. astrigera. We suggest that Pseudomonas versuta (belonging to Proteobacteria) and Rhodococcus erythropolis (belonging to Actinobacteriota) may have the potential to play key roles in overwintering P. astrigera.
... The contribution of general (polyphagous) predators in suppressing pest populations can be significant, especially if they appear early in pest development, facilitating the action of specialised predators later in the season [28]. According to [49], general predators can be considered effective biocontrol agents if they meet the following criteria: ...
The accessible literature covered in this paper commonly highlights psyllids as a significant group of insects affecting pear trees, posing a continual challenge for commercial orchards. With the development of modern pear cultivation systems, Cacopsylla pyri Linnaeus 1758 (Hemiptera: Psyllidae) has emerged as a major pest in pear orchards across many European countries, including those in the Western Balkans. For years, the agricultural sector has primarily relied on chemical insecticides to control pear psyllas, but these methods often fail to produce satisfactory results. This is largely due to C. pyri’s rapid development of resistance to chemical treatments. Consequently, modern agriculture is increasingly shifting towards biological methods to manage C. pyri, involving the identification and conservation of its natural enemies. Although there is an abundance of research on the natural predators of C. pyri and their biocontrol applications across the globe, the Western Balkan region has conducted relatively few studies on the subject. Globally, various parasitoids, predators, and entomopathogenic fungi are often cited as effective against C. pyri. Specific species registered in the agroecological conditions of the Western Balkans include parasitic wasps such as Trechnites insidiosus Crawford, 1910 (Hymenoptera: Encyrtidae) and Prionomitus mitratus Dalman, 1820 (Hymenoptera: Encyrtidae), as well as the predatory bug Anthocoris nemoralis Fabricius, 1794 (Hemiptera: Anthocoridae). However, most Balkan countries have yet to fully utilise the potential of beneficial entomofauna or develop strategies for their commercial application at a national level. Considering that C. pyri is a major pest in pear cultivation and its natural enemies have not been thoroughly explored in most of the Western Balkans, this paper aims to review the literature data on available natural enemies of pear psyllas and to highlight and promote their undeniable potential in biological control.
... Trophic interactions of generalist predators can be influenced by various factors, such as changes in prey density, seasonal variations of prey availability, pesticide applications, and harvest practices [1,7,[24][25][26][27]. Predators in agricultural ecosystems are also influenced by management type [28]. ...
Spiders act as one of the major predators among arthropods in agroecosystems and are crucial to the control of pest densities. As they are almost exclusively predators, they have developed a number of hunting strategies, which have consequently impacted their complex trophic interactions. The development of molecular biology methods for environmental DNA analysis has made it easier to analyze such complex trophic networks. In order to ascertain the trophic interactions of spiders, a sampling of spider species was carried out in two olive groves in Zadar County, Croatia, under integrated and ecological pest management. To construct the trophic networks of spiders, we performed DNA metabarcoding. The combined general and spider-excluding primers were able to recognize prey from 12 distinct orders in the guts of the 57 spiders. According to our results, spiders have a complex trophic network that exhibits seasonal and site-specific variations. The results obtained from both sites having different pest management also confirmed that spiders consumed phytophagous insects in the highest ratio, including some important pests, in comparison to other prey and that management and guild type had an impact on the predation of phytophagous insects.
... Diagnostic PCR technology based on specific primer amplification has become a common method to study the trophic interactions among arthropods [32][33][34], especially in open habitats with complex trophic interactions. For example, Lenka et al. [35] detected the DNA of natural predators Anyphaena and Philodromus in orchards, and found that the frequency of the two kinds of spider species' predation on pear psylla was much higher than that of IGP. Ortiz-Martine et al. [10] revealed the frequency of IGP among ladybeetles and parasitoids in wheat fields under different landscape backgrounds. ...
Simple Summary
When there are multiple natural enemies in the same ecosystem, intraguild predation between natural enemies will affect the population dynamics of target organisms and the effectiveness of biological control. It is necessary to study this relationship in depth to enhance the function of biological control. Hippodamia variegata (Goeze) and parasitoids are two types of dominant natural enemies of the cotton aphid Aphis gossypii Glover in Xinjiang, China. Among them, the ladybeetle preys on common aphids as well as parasitoids. This study measured the feeding choices of H. variegata towards mummies with different densities of A. gossypii. Meanwhile, investigation and sampling in the cotton field were conducted from 2017 to 2019. The predation of H. variegata individuals on aphids and mummies was detected using diagnostic PCR. The results showed that H. variegata had no obvious feeding preference towards live aphids and mummies, and preferred denser prey. The molecular detection results show that A. gossypii was the main prey source and medium of consumption of parasitoids for the ladybeetle. H. variegata had strong trophic links to both parasitoids and aphids. The above information is crucial for evaluating the pest control ability of H. variegata more comprehensively and strengthening the strategies for the biological control of aphids.
Abstract
Intraguild predation among arthropod predators in agricultural ecosystems may have a negative impact on biological control. At present, there are few direct reports on trophic relationships among participants of predation in field groups. In this study, we measured the feeding choices of Hippodamia variegata (Goeze) towards mummies with different densities of Aphis gossypii Glover. The dynamics of the occurrence of mummies in the cotton field were investigated over 2017–2019. Singleplex PCR and multiplex PCR were used to detect the predation of 2090 H. variegata individuals on aphids and mummies in Xinjiang cotton field, which revealed the intraguild predation frequency between H. variegata and various parasitoids. There was no obvious feeding preference of H. variegata towards live aphids or mummies, which mainly depended on the relative density of prey. Among the four species of aphids detected in H. variegata, A. gossypii had a high detection rate and was the main prey source of the ladybeetle in the cotton filed. Mostly, ladybeetles consumed parasitoids through mummies, with 6.39% directly feeding on adult parasitoids. H. variegata had strong trophic links to both parasitoids and aphids. We established a food web of aphids–primary parasitoids–hyperparasitoids–H. variegata, which can be used to evaluate the pest control ability of H. variegata from a new perspective.
... Despite evidence existing for the biocontrol potential of many other web-building spiders (Chapman et al., 2013;Vink & Kean, 2013), Michalko et al. (2019) found in a global metaanalysis that web-building spiders have a poor, often negative effect on pest suppression. Many such spiders also negate their own biocontrol activity through high incidences of intraguild predation (Cuff, Tercel, et al., 2022;Hambäck et al., 2021;Petráková et al., 2016). ...
1. Candy-striped spiders (Enoplognatha spp.; Araneae: Theridiidae) are among Britain's commonest theridiid spiders and are potential immigrant biocontrol agents of many pests in arable fields. Though the presence of these spiders in proximity to agriculture is dependent on the availability of suitable leaves for their egg deposition, their preference for different plant species and habitat types has not been fully investigated.
2. Candy-striped spiders were observed in leaf-rolls during transect surveys of semi-natural habitats (hedgerow, woodland and grassland) adjacent to oilseed rape fields at 10 sites across northeast England in August and September 2021. The local plant community was surveyed and compared against the leaves used by candy-striped spiders via null models.
3. Candy-striped spiders preferentially deposited their eggs in hedgerow, demonstrating relative avoidance of woodland and grassland. They exhibited preference for bramble , common nettle and hogweed leaves, but also used those of dock, ash and black-thorn. Candy-striped spiders appeared to preferentially use leaves with roughly equal length and width and avoided longer, narrower leaves irrespective of their total size.
4. The leaves used by candy-striped spiders are taxonomically broad, but share some morphological commonalities. Candy-striped spiders exhibit some degree of generalism, regularly utilizing suboptimal leaves in sites lacking their preferences.
... While we observed adverse effects of Proteus, matrine, and pyridalyl on the consumption rate of O. laevigatus, they do so to varying degrees. The reduced consumption rate of prey by this predator may be due to several factors, i.e., antifeedant and repellency effect of insecticides, the altered taste of prey, and altered potency of predator (Castro et al. 2013, Petrakova et al. 2016, Michalko and Pekár 2017. These results are in agreement with what was reported in previous studies where the exposure of predators to a residue of insecticides negatively affects their feeding behavior (Sitvarin andRypstra 2014, Tahir et al. 2019). ...
Proteus, matrine, and pyridalyl were tested in the laboratory for their effects upon Orius laevigatus (Fieber), which is a polyphagous predator used for IPM programs of Frankliniella occidentalis (Pergande). Against female adults, the most toxic insecticide was Proteus (LC50 = 44.3 µl L-1), followed by pyridalyl (LC50 = 83.8 µl L-1) and matrine (LC50 = 102.7 µl L-1). The mortality of female adults was checked 24, 48, 72, and 96 h after exposure to 14-d residues of the treatments on strawberry leaves. The residual of Proteus was less toxic; the remaining products caused the lowest mortality at different times after exposure. Sublethal treatments (LC25) significantly prolonged the developmental duration of total immature stages from 17.6 d in control to 21.6 and 20.0 d in Proteus and pyridalyl treatments, respectively. Also, the fecundity of O. laevigatus treated with Proteus, pyridalyl, and matrine decreased to 58.8%, 75.6%, and 96.7%, respectively, in comparison to the control. Compared with the control population (0.118 d-1), the intrinsic rate of increase (r) of F1 generation decreased by 0.053, 0.095, and 0.110 d-1 in Proteus, pyridalyl, and matrine treatments, respectively. The consumption rate of control bugs reached 14.0 thrips during 24 h. The adults fed on Proteus treatment had the lowest consumption rate in this period (9.4 preys). Overall, matrine proved to be harmless with reproductive capacity and r similar to what was recorded in control bugs. We concluded that matrine can be used as an alternative for the synthetic insecticide to integrate with O. laevigatus.
... In addition, blocking primers may lead to the risk of nonspecific coblocking when prey and predators are phylogenetically close (Piñol et al., 2014). Our results showed that O. alboannulata preys on some spider species in Lycosidae, Araneidae, Pisauridae, Salticidae, Tetragnathidae, and Theridiidae (Table S6), that is, intraguild predation (Petráková et al., 2016). ...
As one of the most abundant predators of insects in terrestrial ecosystems, spiders have long received much attention from agricultural scientists and ecologists. Do spiders have a certain controlling effect on the main insect pests of concern in farmland ecosystems? Answering this question requires us to fully understand the prey spectrum of spiders. Next‐generation sequencing (NGS) has been successfully employed to analyze spider prey spectra. However, the high sequencing costs make it difficult to analyze the prey spectrum of various spider species with large samples in a given farmland ecosystem. We performed a comparative analysis of the prey spectra of Ovia alboannulata (Araneae, Lycosidae) using NGS with individual and mixed DNA samples to demonstrate which treatment was better for determining the spider prey spectra in the field. We collected spider individuals from tea plantations, and two treatments were then carried out: (1) The DNA was extracted from the spiders individually and then sequenced separately (DESISS) and (2) the DNA was extracted from the spiders individually and then mixed and sequenced (DESIMS). The results showed that the number of prey families obtained by the DESISS treatment was approximately twice that obtained by the DESIMS treatment. Therefore, the DESIMS treatment greatly underestimated the prey composition of the spiders, although its sequencing costs were obviously lower. However, the relative abundance of prey sequences detected in the two treatments was slightly different only at the family level. Therefore, we concluded that if our purpose were to obtain the most accurate prey spectrum of the spiders, the DESISS treatment would be the best choice. However, if our purpose were to obtain only the relative abundance of prey sequences of the spiders, the DESIMS treatment would also be an option. The present study provides an important reference for choosing applicable methods to analyze the prey spectra and food web compositions of animal in ecosystems. Individual DNA sample sequencing obtains the accurate prey spectrum of spiders. Mixed DNA sample sequencing underestimates the prey spectrum of spiders. Individual and mixed DNA sample sequencing obtains almost the same relative abundance of prey sequences of spiders.
... The complexity of trophic interactions in the spider part of the orchard food webs (for a recent review on spider predation ecology see Michalko et al., 2019) is well illustrated by Philodromus spiders. Philodromus spiders are not only involved in intraguild interactions as both prey and predator (Fig. 4), they are also known to feed heavily on aphids and psyllids in orchards (Gajski & Pek ar, 2021;Korenko et al. 2010;Lefebvre et al., 2017;Mez€ ofi et al., 2020;Pek ar, Michalko, Loverre, Líznarov a, & Cernecka, 2015;Petrakova et al., 2016), even though predation may vary by orders of magnitude seasonally between sites. We found aphid DNA in 3 of 17 (18%) Philodromus individuals in Spain and in 37 of 125 (30%) individuals in Sweden, but only 9% contained psyllid DNA. ...
Understanding the full diet of natural enemies is necessary for evaluating their role as biocontrol agents, because many enemy species do not only feed on pests but also on other natural enemies. Such intraguild predation can compromise pest control if the consumed enemies are actually better for pest control than their predators. In this study, we used gut metabarcoding to quantify diets of all common arachnid species in Swedish and Spanish apple orchards. For this purpose, we designed new primers that reduce amplification of arachnid predators while retaining high amplification of all prey groups. Results suggest that most arachnids consume a large range of putative pest species on apple but also a high proportion of other natural enemies, where the latter constitute almost a third of all prey sequences. Intraguild predation also varied between regions, with a larger content of heteropteran bugs in arachnid guts from Spanish orchards, but not between orchard types. There was also a tendency for cursorial spiders to have more intraguild prey in the gut than web spiders. Two groups that may be overlooked as important biocontrol agents in apple orchards seem to be theridiid web spiders and opilionids, where the latter had several small-bodied pest species in the gut. These results thus provide important guidance for what arachnid groups should be targets of management actions, even though additional information is needed to quantify all direct and indirect interactions occurring in the complex arthropod food webs in fruit orchards.
... The basic theoretical models predict a limited space for the coexistence of a top predator and a mesopredator along a productivity gradient (Polis andHolt 1992, Holt andPolis 1997). Despite these theoretical predictions and a high degree of IGP in spider communities (Petráková et al. 2016, Roubinet et al. 2017, Mezőfi et al. 2020, such communities are often extremely diverse across various ecosystems (forests: Černecká et al. 2020;grasslands: Košulič et al. 2014;agroecosystems: Mader et al. 2017). The hunting strategies of generalist spiders determine the relative capture of conspecifics and heterospecifics, which may affect the coexistence mechanisms and assembly of spider communities. ...
Intraguild predation (IGP) is a common interaction between generalist predators when they competitively exploit similar resources and prey on each other. Theoretical models predict limitations for intraguild predator coexistence unless some mechanisms, such as the utilization of alternative prey (i.e. trophic niche partitioning) and cannibalism, increase the relative intraspecific clustering and interspecific segregation. As hunting strategies determine trophic niches of predators and their own vulnerability to predation, the hunting strategies may also determine the relative importance of cannibalism, predation, and exploitative competition and consequently the intensity of IGP. The importance of hunting strategies on the potential outcome of IGP and how habitat properties modify the interaction between hunting strategies remain poorly understood. Using published data on spider prey of spider predators, we first investigated how predation of a top‐predator on a mesopredator is determined by the functional distance between both predators to understand how predation and exploitation are distributed in spider communities. Subsequently, we investigated the predation among spiders with particular hunting strategies to understand which strategies interact most frequently. We also investigated whether the interaction between hunting strategies was influenced by habitat type (forest, open (semi)natural habitat, agroecosystem) or by habitat stratum (ground versus vegetation). The hunting strategies of top‐predators and mesopredators interacted to determine the relative capture proportions of conspecifics and hetero‐specifics. This interaction was further modified by habitat type and stratum. Two mechanisms can reinforce coexistence in highly diverse spider communities. First, top‐predators preyed most frequently on functionally distinct mesopredators, which indicates the overall intensity of IGP may be relaxed by a balanced distribution between exploitative competition and predation. Second, cannibalism was common for top‐predators with a hunting strategy of frequently preying on functionally similar mesopredators. Cannibalism may lead to self‐limitation of top‐predator populations and may thereby facilitate coexistence between two predator species.
... However, traps did not seem to be effective for two other very common families, Oxyopidae and Thomisidae, which might be because these spiders prefer to use leaves to make their shelters (Foelix, 2011). Anyphaenidae spiders (represented by a common species in our traps) are generalist predators and have the potential to be used as biological control agents of different pests (Pekár et al., 2015;Petráková et al., 2016). In addition, we found one gnaphosid species colonizing trap-nests in alfalfa crops. ...
Semi-natural habitats in agricultural landscapes offer reproduction and feeding sites for natural predators of pests. Spiders are among the most abundant and diverse generalist predators and can efficiently suppress pest populations in agroecosystems. However, despite the importance of these habitats, there is a significant gap of knowledge on oviposition sites of spiders in agroecosystems. Our main goal was to investigate if semi-natural habitats play an important role in spider oviposition in two crops with different agricultural managements. Our specific objectives were to estimate where spider oviposition is highest (in semi-natural habitats or in crops); if there are different responses between crops (alfalfa and soybeans); and to measure trap-nests efficiency as shelter and breeding places for vegetation-dwelling spiders. We used trap-nest technique, a novel method to collect spiders and their eggsacs. We carried out the study in 15 sites in soybean and 10 sites in alfalfa crops in order to sample spiders' eggsacs and shelters. Each sampled site consisted of a semi-natural habitat (enclosures or edges) and its adjacent crop. We found that the number of eggsacs decreased from semi-natural habitats towards the interior of the soybean crop and the opposite pattern in alfalfa, where the number of eggsacs significantly increased within the crop. Our results provide evidence that spider reproduction takes place outside the crops, albeit only in soybean crops. Our findings were different in alfalfa with minimum use of agrochemicals and with a lesser seasonal disturbance, with a higher spider oviposition compared to semi-natural habitats. In addition, our results have several important implications for the management of agroecosystems. We consider that the use of these trap-nests is a suitable and a reliable tool to study vegetation-dwelling spiders in different ecosystems.
... Specifically, during winter and early spring, some winter-and early-spring -active spider species feed in particular on pests due to absence of alternative prey. These spiders can markedly decrease pest density Pekár et al. 2015;Petráková et al. 2016;Lefebvre et al. 2017). ...
There are various modern pest-control management systems used in the current apple production, such as integrated pest management (IPM) or organic systems. All aims to support occurrence of natural enemies that should help to reduce populations of pests. Here we investigated the effect of fungicide-treated and fungicide-free (resistant tree varieties) treatment combined with biological, IPM, and conventional systems on spiders, as the major group of natural enemies occurring on foliage of apple trees. The biological treatment was based on the use of biopesticides; IPM system was based on the use of selective insecticides, conventional included the use of broad-spectrum insecticides. Abandoned plot served as a control. The study was done for three consecutive years. Spiders were sampled from canopies by beating at weekly intervals during season. We found that fungicide-treated plots had lower abundance of spiders for two years but not species richness than fungicide-free plots. Among the three pest-control management systems, IPM and conventional supported greater spider abundance but not species richness than the biological treatment. Comparison of spider abundance before and after insecticide applications revealed that only very few pesticides, particularly the broad-spectrum ones, reduced spider numbers. In addition, we focused on the comparison of three traits (body size, maturity, fecundity) among treatments. Of six species, only Philodromus cespitum showed a smaller body size on biological than the other treatments. There were three species in which adults occurred earlier on conventional treatment than on the other treatments. Neither clutch size of Phylloneta impressa nor egg size was different among treatments. The small though significant differences in abundance, richness, and selected traits, found among IPM, conventional, and biological treatments and the control show that these pest-control management systems had similar effect on spiders. Use of IPM system combined with scab resistant apple varieties is recommended.
... Temperature had a significant effect on the probability of the resettlement of inspected and emptied nesting boxes by A. accentuata, which was the most active species during winter [26,49]. This species and some species of Philodromus are winter-active predators and prey even at temperatures close to 0 • C [48]. ...
Simple Summary
Nesting boxes are often used to support hole-nesting birds, but are also attractive as a shelter for many invertebrates, especially for overwintering. We studied assemblages of spiders overwintering in nesting boxes in a lowland forest and the factors influencing their abundance and activity during winter. The results show that the majority of arboreal spider species use nesting boxes to overwinter and that their abundance increases with the presence of nest material. Some spider species are also active at low temperatures in winter and can resettle emptied nesting boxes during the winter season. By hanging nesting boxes on trees, ornithologists support not only hollow nesting birds, but also overwintering spiders.
Abstract
Spiders are common inhabitants of tree hollows, as well as bird nesting boxes, especially in autumn and winter. Some species of spiders use bird nesting boxes for overwintering. We investigated spider assemblages in nesting boxes and how temperature influences the abundance of overwintering spiders in nesting boxes in lowland forest in the Czech Republic. The study was conducted in the European winters of 2015–2017. In total, 3511 spider specimens belonging to 16 identified species were collected from nesting boxes over three years in late autumn and winter. Almost all species were arboreal specialists. The dominant species were Clubiona pallidula, Anyphaena accentuata, Platnickina tincta, and Steatoda bipunctata. Although the tree species had no effect on the abundance of overwintering spiders, the presence of nest material affected the abundance of spiders in the nesting boxes (preferred by C. pallidula and P. tincta). In general, spiders resettled nesting boxes during winter only sporadically, however A. accentuata reoccupied boxes continuously, and its activity was positively correlated with the outside temperature. Nesting boxes support insect-eaters all year around—birds during spring and summer and spiders during autumn and winter.
... In addition, Ph. cespitum also feeds on other pests (Klein, 1988;Wisniewska & Prokopy, 1997;. This spider remains active during winter when other predators are dormant, and consequently, it can also reduce, for example, overwintering psyllid populations Petráková et al., 2016). Philodromus cespitum is among the most abundant hunting spiders in the canopy of apple orchards both in Europe Pekár, 1999;Markó et al., 2009) and North America , and in our study it consumed the second-highest number of pests Table S2.6), which suggests that clubionids are more compatible with biological control than several other hunting spiders. ...
Spiders (Araneae) form abundant and diverse assemblages in agroecosystems such as fruit orchards, and thus have an important role as natural enemies of orchard pests. Although spiders are often considered to be polyphagous and opportunistic predators in general, limited information is available on their natural prey at both species and community levels. Furthermore, many other aspects of the biology of the species with potential economic importance are poorly known. Thus, the aims of this thesis were (1) to provide new data on the taxonomic composition of spider assemblages inhabiting apple orchards; (2) to assess the natural prey (realized trophic niche) of arboreal hunting spiders, their role in trophic webs and their biological control potential with direct observation of predation events in apple orchards; and finally, (3) to get more information on the circadian biology regarding the locomotor activity of the two most abundant arboreal hunting spider species (Carrhotus xanthogramma and Philodromus cespitum) in apple orchards.
... The winter-active spider species present in pear orchards engage in IGP events; however, the frequency of the IGP observed was low compared to their consumption of pests (pear psyllids). Therefore, at least in this case, the negative disservices of IGP were counterbalanced by their efficacy of biological control on a target pest [60]. In a recent landscape study, IGP was found to be low, and did not impact predation on aphids, which supports the natural enemy hypothesis, i.e., that greater diversity of natural enemies leads to more effective biological control [53]. ...
Simple Summary
With increasing human populations and the need for ecosystem services to work in synergy with the production of specialty crops, the maintenance of biodiversity is becoming increasingly important. The aims of this study were to review the current literature employing molecular analysis to reveal the roles of species in providing biological control in agricultural systems. Decrypting the trophic networks between biological control agents and agricultural pests is essential to build eco-friendly strategies that promote the natural management of pests before any mediations, such as chemical control strategies, are required. It was found, during the review process, that our understanding of biological control communities is lacking in many agricultural systems, including common fruit and vegetable production, both in terms of what species are doing for crop production, and how various environmental challenges (i.e., land-use and habitat management concepts, such as wildflower borders) influence species interactions and the delivery of biological control services. New techniques harvesting the power of DNA to reveal species’ roles in specialty crops are an avenue forward to help integrate natural pest management into our standard operating procedures.
Abstract
Biodiversity is an essential attribute of sustainable agroecosystems. Diverse arthropod communities deliver multiple ecosystem services, such as biological control, which are the core of integrated pest management programs. The molecular analysis of arthropod diets has emerged as a new tool to monitor and help predict the outcomes of management on the functioning of arthropod communities. Here, we briefly review the recent molecular analysis of predators and parasitoids in agricultural environments. We focus on the developments of molecular gut content analysis (MGCA) implemented to unravel the function of community members, and their roles in biological control. We examine the agricultural systems in which this tool has been applied, and at what ecological scales. Additionally, we review the use of MGCA to uncover vertebrate roles in pest management, which commonly receives less attention. Applying MGCA to understand agricultural food webs is likely to provide an indicator of how management strategies either improve food web properties (i.e., enhanced biological control), or adversely impact them.
... For several species of spiders, continuous predation on psylla throughout the winter has been shown (Petráková et al., 2016). According to Michalko et al. (2017), spiders active in winter, namely, Anyphaena accentuata and Philodromus ssp., significantly reduce the psylla population density. ...
2021): The effects of various pest control regimes on the community structure and population dynamics of selected natural enemies of Cacopsyllapyri in pear orchards, Biocontrol Science and Technology To link to this article: https://doi. ABSTRACT The effects of three different pest control regimes in three pear orchards (two with integrated pest management regimes and one with an organic farming regime) on communities of arthropods were studied in a two-year experiment. Insects were collected in three stages by beating the lower branches of trees. The number of species and other taxa of natural enemies increased with the reduction in insecticide applications. A total of 2,492 individuals of 145 species and other taxa were found in the samples from the three pear orchards with different pest management practices. The most numerous groups were Araneae, with 44 species, and Coleoptera, with 42 species, followed by Hymenoptera, with 33 taxa, and Heteroptera, with 24 species. Of the total number of taxa, the share of entomophagous arthropods was, on average, 62.6%. The share of predaceous individuals was, on average, 63.7% of the total number of individuals. The number of dominant predaceous species decreased with an increase in the diversity of species and other taxa. A significant relationship was found between the number of C. pyri adults and the Shannon-Wiener index of diversity for the predaceous taxa. It was demonstrated that generalist predators and their diversity have an important influence on the regulation of pear psylla in the vegetative period. ARTICLE HISTORY
... The results also showed that the spiders respond to the frequency of disturbance and management, changing their family representation. Also, the prevalence of a euryphagous diet in agroecosystems results in a benefit in terms of controlling pests (Petráková et al. 2016). Our findings contribute to knowledge about what is going on within plots, which taxa are sensitive to disturbance and management regimes, and which traits enable them to be resilient to the agroecosystem dynamics. ...
Deforestation and land-cover changes have transformed the Argentinian Dry Chaco into a mosaic dominated by crops and ranch fields. Although land-use activities are seen as one of the major driving forces of biodiversity loss, the specific impacts in this ecoregion are poorly understood. In this study, we analyse the effects of land uses and management on ground-dwelling spiders in agroecosystems of the Dry Chaco, in the North of Argentina. We identified four land-use classes: secondary forests, pastures, orchards, and crops. Additionally, 15 environmental variables were recorded within these land-use classes. Management, tree cover and species richness of trees, shrubs and herbs were the most important variables determining spider community composition. Three families, lycosids (Lycosidae), thomisids (Thomisidae), and zodariids (Zodariidae), were associated as taxonomic indicators as well as functional indicators of the different groups of land uses; thus suggesting that functional traits of ground-dwelling spiders reflect habitat changes within the agricultural landscape they inhabit.
... Alternatively, the nutritional quality of prey might remain similar, but the adult females had larger body size advantage and spider prey became less dangerous (Michalko & Pekár, 2015), which enabled sufficient food intake. Indeed, P. cespitum generally prefers hemipterans over spiders (Michalko & Pekár, 2015Petráková et al., 2016;Michalko & Dvoryankina, 2019). However, at significantly lower prey to predator body size ratio, spiders become its preferable prey (Petcharad et al., 2018). ...
1. Intraguild predation (IGP) among generalist predators significantly affects the food web dynamics but the benefits of IGP for top predators are still unclear.
2. We offered diets consisting of aphids, of spiders, and their sequential mix (i.e. polytypic diet) to the spider Philodromus cespitum and measured its survival, weight, development, and fecundity. To avoid a species‐specific effect, the aphid and spider prey consisted of several similarly sized species.
3. The spider diet prolonged survival in comparison to starvation while the aphid and polytypic diets enabled the highest survival of juveniles. The spider diet resulted in low weight gain and slow development in juveniles at the population level. However, the weight change was highly variable among individuals, and a substantial portion of the individuals engaging in IGP gained the most weight compared to other diets. The aphid and polytypic diets resulted in the largest weight increase and fastest development in juveniles at the population level, and there was little variability in the amount of weight gained among individuals. Diet did not affect survival of adult females, but females on the spider and polytypic diets had higher fecundity than those on the aphid diet.
4. While both the aphids and the spiders had energetic and nutritional value for Philodromus cespitum, a polytypic diet consisting of a mix of them improved overall fitness. IGP therefore seems to be an adaptive strategy of Philodromus cespitum, and IGP on small spiders may increase its performance in ecosystems where aphids are highly dominant pests.
... Acknowledgement that spiders are an effective biocontrol agent has existed for Correspondence: School of Biosciences, Cardiff University, Museum Avenue, Cardiff, CF10 3AX. cuffjp@cardiff.ac.uk decades (Riechert & Lockley, 1984;Sunderland et al., 1997;Sunderland, 1999) since they regularly consume pests such as aphids (Sunderland et al., 1986;Beck & Toft, 2000;Mayntz & Toft, 2000;Bilde & Soren, 2001;Harwood et al., 2003;Nyffeler & Sunderland, 2003), planthoppers (Wang et al., 2016;Wang et al., 2017), psyllids (Petráková et al., 2016), medflies (Monzó et al., 2010), lepidopterans (Quan et al., 2011;Pérez-Guerrero et al., 2013;Senior et al., 2016), and weevils (Vink & Kean, 2013). Whilst crop rotation disrupts biocontrol by many generalist predators, spider generation times often coincide with crop cycles, with early pest population establishment coinciding with peak spider abundances in Spring, thus facilitating early pest suppression (Riechert & Lockley, 1984;Symondson et al., 2002;Harwood & Obrycki, 2005;Welch et al., 2011). ...
1. Money spiders (Linyphiidae) are an important component of conservation biological control in cereal crops, but they rely on alternative prey when pests are not abundant, such as between cropping cycles. To optimally benefit from these generalist predators, prey choice dynamics must first be understood.
2. Money spiders and their locally available prey were collected from cereal crops two weeks pre- and post-harvest. Spider gut DNA was amplified with two novel metabarcoding primer pairs designed for spider dietary analysis, and sequenced.
3. The combined general and spider-exclusion primers successfully identified prey from 15 families in the guts of the 46 linyphiid spiders screened, whilst avoiding amplification of Erigone spp. The primers show promise for application to the diets of other spider families such as Agelenidae and Pholcidae.
4. Distinct invertebrate communities were identified pre- and post-harvest, and changes in spider diet and, to a lesser extent, prey choice reflected this. Spiders were found to consume one another more than expected, indicating their propensity toward intraguild predation, but also consumed common pest families.
5. Changes in spider prey choice may redress prey community changes to maintain a consistent dietary intake. Consistent provision of alternative prey via permanent refugia should be considered to sustain effective conservation biocontrol.
... These techniques allow for quantification of the contributions of predators to biological control of a target pest (Boreau De Roincé et al., 2013;Lundgren et al., 2009;Renkema et al., 2014;Yang et al., 2017aYang et al., , 2017b, which have illustrated that biological control is not always predictable based on predator abundance (Harwood et al., 2007b). These techniques can also aid in elucidating several drivers influencing predator richnessbiological control relationships such as the frequency of intraguild predation (Davey et al., 2013;Ingels et al., 2013;Petráková et al., 2016;Roubinet et al., 2017;Traugott et al., 2012;Yang et al., 2017aYang et al., , 2017b, temporal activity patterns (Jelaska et al., 2014Whitney et al. 2008, life stage of the predator (Harwood et al., 2009), and alternative prey density (Harwood et al., 2007b(Harwood et al., , 2007a(Harwood et al., , 2004Krey et al., 2017;Roubinet et al., 2017;Staudacher et al., 2006;Symondson et al., 2000), as well as organic versus conventional farming practices and habitat management (Balmer et al., 2013;Heimoana et al., 2017;Ingrao et al., 2017;Krey et al., 2017;Lefebvre et al., 2017;Roubinet et al., 2017;Szendrei et al., 2014Szendrei et al., , 2010. ...
The biodiversity-ecosystem function (BEF) hypothesis predicts that increased richness within a trophic level supports greater resource capture. However, higher predator richness commonly found within organic compared to conventional agroecosystems does not always result in enhanced pest suppression. The striped cucumber beetle, Acalymma vittatum (Coleoptera: Chrysomelidae), causes damage via direct feeding and pathogen transmission to crops in the family Cucurbitaceae. The aims of this study were to: 1) identify the predators that contribute to A. vittatum suppression using molecular gut content analysis, 2) determine if the richness of predators testing positive for A. vittatum DNA was negatively correlated with prey abundance, and 3) examine how organic versus conventional cucurbit production influenced these relationships. Using a species-specific primer for A. vittatum, we found that a diverse community of predators feed on this pest, including Carabidae, Coccinellidae, Formicidae, Henicopidae, Opiliones, Lycosidae, and Staphylinidae. The richness of predators testing positive for A. vittatum DNA within a cucurbit field was negatively correlated with pest abundance, supporting the BEF hypothesis. We found no effect of farm management on the proportion or richness of predators testing positive for pest DNA, despite a 43.4% greater pitfall trap catch of predatory taxa within organic fields. This illustrates that using traps to measure predator richness and abundance may not accurately predict the strength of biological control service provided by a guild of natural enemies. Application of molecular gut content analysis proves a useful tool in advancing both the theory and practice of conservation biological control.
... Collembolans are important prey for the foliage hunting spiders like Philodromus spp. and Anyphaena accentuata that dominated the community Pek ar 2015, 2016;Petr akov a et al. 2016). Such a reduced prey supply might enhance emigration and IGP and reduce the natality of spiders (Rickers et al. 2006;Oelbermann et al. 2008;Schmidt et al. 2014;Tsutsui et al. 2016). ...
The management practices in agroecosystems can alter the community structure of pests' natural enemies, which can consequently disturb their biocontrol function. Here, we investigated how organic or conventional farming influence the community structure of arthropod predators (spiders, coccinelids, anthocorids, ants) in orchards. The three conventional orchards studied were plum tree monocultures where mainly fungicides were applied. The three organic orchards studied were dominated by plum trees with admixture of apple trees and no agrochemical was applied. We found that management significantly affected only spiders that were less abundant in the conventional orchards than in the organic orchards. In addition, the conventional management resulted in reduced species density and altered the community composition of spiders. The conventional management reduced the functional dispersion of spider body size, which may narrow the size-spectrum of pests that could be reduced by spiders. The conventional management also reduced abundances of foliage hunters and space-web spiders. Since these spiders are effective against various insect pests, the conventional management of applying fungicides might result in increased crop damage via increased insect pests.
... The small individuals that are prone to the intraguild predation may trade-off foraging for safety (Stephens et al., 2007). The strong intraguild predation could be evinced by the larger philodromids and / or Anyphaena accentuata (Walckenaer, 1802) (Anypahenidae) which are the dominant top predators in the trees of the studied orchard and have been found to prey on each other (Korenko and Pekár, 2010;Michalko and Pekár, 2015b;Petráková et al., 2016). Indeed, the adult philodromid females from orchard centres had higher capture rates and also preyed upon a larger range of spider body size than the females from hedgerows and were therefore more dangerous for smaller spiders. ...
Seminatural habitats adjacent to crops often increase density and diversity of pests' natural enemies in crops. However, there is no research investigating the effect of seminatural habitats on the intraspecific variation in functional traits of the pests' natural enemies in agricultural landscapes, despite its significant impact on pest control. Here, we investigated whether there is intraspecific variation in functional traits of a potential bio-control agent, the generalist spider Philodromus cespitum, depending on the location in an agricultural landscape. We compared size, capture rate, and fundamental trophic niche of P. cespitum along five transects (60 m) each consisting of three plots: hedgerow adjacent to an apple orchard, orchard edge, and orchard centre. The individuals from the orchard centers were larger than the individuals from orchard edges and hedgerows. Large individuals from the orchard centers had higher capture rate than large individuals from hedgerows but in small individuals it was the opposite. The adult females from the centers had a wider trophic niche than those from hedgerows, indicating higher foraging opportunism. The individuals from orchard edges had moderate phenotype in both trophic traits. The individuals from the orchard edges were also the most heterogeneous in body size and capture rate. The results show a clear edge effect which means that the hedgerows influenced the in-traspecific functional composition in the orchard. As the intraspecific variation can interact with the species' densities in influencing pest control, ignoring the intraspecific variation in the agricultural landscape and crops may lead to an inaccurate inference about the biocontrol services provided by spiders.
... aureolus group certain species are quite diffi cult to separate, because they diff er only in small details of their copulatory/ genital organs. Furthermore, the identifi cation is made more diffi cult by the fact that diff erent species in Ph. aureolus group can occur sympatrically in the same habitat (Petráková et al. 2016). Philodromus buchari (Figs 1-8) may be mostly confused with Ph. aureolus (Fig. 9), Ph. cespitum (Fig. 10) or Ph. ...
Philodromus buchari Kubcová, 2004 is reported for the first time from Hungary. A relatively large and abundant population of Ph. buchari was found in Diósd (near Budapest), and after examining other materials, it seems that the species is widespread throughout the country. In the past Ph. buchari was misidentified as Ph. aureolus (Clerck, 1757), Ph. cespitum (Walckenaer, 1802) or Ph. longipalpis Simon, 1870, and possibly it is a native species in Hungary. It may have a wider distribution in Europe and the Mediterranean region as previously was thought. Copulatory/genital organs and habitus of Ph. buchari are illustrated. With 11 figures.
... This expectation is consistent with our results, as interviewees were more uncertain about beneficial effects of nocturnal earwigs compared with predators which can be active during the day, such as syrphids, coccinellids, and lacewings. Specialized techniques such as video-recording (Frank et al., 2011) and molecular analyses (Petráková et al., 2016;Romeu-Dalmau et al., 2012) can be helpful in providing direct evidence on the roles of difficult-to-observe natural enemies. In Central Washington, researchers have spread information on enhancing biological control to apple industry decision-makers through interactive on-farm experiences and internet resources (Gadino et al., 2016). ...
In agroecosystems, omnivores can be beneficial predators or harmful herbivores. In apple orchards, the omnivorous European earwig (Forficula auricularia) is thought to be a key predator of woolly apple aphid (Eriosoma lanigerum), but has also been implicated in feeding on apple fruit. Assessing the effects of earwigs in orchards is difficult because they are nocturnal, and their damage to fruits can resemble other wounds. Apple orchardists thus may manage earwigs as either predators or pests based on subjective opinions. To understand current opinions on earwigs in apple orchards, we interviewed 15 apple pest management decision-makers in Washington State, USA. To compare opinions to objective measurements, we manipulated earwig abundance within plots at four orchards and collected data on fruit damage, woolly apple aphid abundance, and molecular gut contents of earwigs. Most interviewees thought earwigs were aphid predators, but some thought earwigs could be minor pests, and most were more uncertain about earwigs’ effects relative to other aphid natural enemies. In the field, earwig abundance was negatively correlated to woolly apple aphid abundance, and earwig guts regularly contained woolly apple aphid DNA, even when aphid densities were low. We found no evidence earwigs damaged fruits. Overall, our results suggest earwigs improved biological control and were not pests, so discontinuing the occasional use of insecticides against earwigs could benefit apple growers. More generally, omnivores and difficult-to-observe natural enemies could often have important underappreciated benefits in agriculture.
... In our study we used immature spiders and this could explain the differences between our results and those found in Paraphysa. The temperature was constant in our experiments, but reports show that in nature, temperature can be an important influence on both feeding and capture rate (Kaltsas et al. 2008;Petrakova et al. 2015). Our results showed that crickets supported the highest mass gain for tarantulas, being more than twice what we found for adult beetles. ...
This is the first study about trophic traits of Grammostola vachoni, a threatened theraphosid spider endemic to the mountain systems of central Argentina. Four prey types were used in experiments: crickets, cockroaches, beetle larvae and adult beetles. Grammostola vachoni was observed to eat at a rate of about once every 11 days, with the mean total number of prey consumed per spider during the experimental period being 2.7. Latency to the first attack was similar for crickets, cockroaches and beetle larvae, but was shorter for adult beetles. Feeding time was significantly longer for crickets and beetle larvae. Mass gain was significantly different among prey types. Feeding effectiveness and ingestion rate were significantly higher for crickets. A significant positive correlation for feeding effectiveness and ingestion rate with prey mass and the initial spider mass was also found.
... It is noteworthy that spiders were the main predators within the apple orchards when the first colony fundatrices (aphids emerging from winter eggs) were present, indicating their importance in the early control of aphids (Isaia, Beikes, Paschetta, Sarvajayakesavalu, & Badin, 2008). Petrakova et al. (2016) also used gut content analysis to detect psyllid predation by Philodromus and Anyphaena in winter and early spring in a pear orchard. They observed a high percentage of spiders with psyllid in their gut contents varying from 10 to 90% for Philodromus and from 40 to 100% for Anyphaena during the first year of their survey. ...
It is well known that spiders are present in high numbers in orchards
and may contribute to biocontrol. Some recent studies in central
Europe further showed that some spiders are active year-round
and consume pests even in winter. Using cardboard traps laid
every two weeks, we carried out a survey to determine which
spider and earwig species are active from September to May in an
experimental, pesticide-free, apple orchard under a Mediterranean
climate. We observed that spider activity was never completely
absent. The structure of the spider communities showed a marked
seasonality in three periods (so-called ‘autumn’, ‘winter’ and
‘spring’). Only two spider genera, Philodromus and Trachelas, were
highly active in winter (percentage of catches during this season
above 40%) and six others (Lathys, Clubiona, Gnaphosa, Theridion,
Phrurolithus) had moderate activity (between 20 and 40%). The
two earwig species had different patterns of winter activity with
Forficula auricularia almost absent whereas F. pubescens was
moderately active on trees. Spider community abundance,
diversity and evenness significantly decreased between autumn
and winter and remained low in the following spring probably
because the attractiveness of the traps is much lower at this time
of year due to mild temperatures and the presence of leaves on
the trees. Winter-active spiders could contribute to pest biocontrol
during the cold season and we advocate that the use of broadspectrum
pesticides at the end of winter, as classically applied in
orchards, may be counter-productive for pest control.
Spiders are important predatory natural enemies in agricultural and forestry ecosystems, yet the role of vision in their predatory behavior remains unclear. In this study, we screened three opsin genes—corresponding to ultraviolet-sensitive and medium-to-long wavelength-sensitive opsins—from the transcriptome sequencing database of Pardosa astrigera. All three genes possess seven transmembrane topological structures and a lysine residue on the second transmembrane domain, which are typical characteristics of opsins. Using quantitative real-time PCR (RT-qPCR), we analyzed the expression patterns of these opsin genes in different tissues, developmental stages, and under the induction of light at three wavelengths. The results showed that all three opsin genes were significantly expressed in the cephalothorax and expressed across developmental stages with no significant differences. Under light induction, their relative expression first increased and then decreased in both male and female adult spiders. Subsequently, RNA interference (RNAi) was used to individually knock down each opsin gene, confirming their involvement in color vision. These results suggest that the three opsin genes are involved in spider vision, laying the foundation for further elucidating the role of vision in spider predation, and offering a new perspective for reducing the unintended killing of natural enemies by insect traps.
Psylla pyri L. is the pear dominant pest, which damage can reach 7090 %. 57 generations of the insect can develop during one growing season in the south of Russia. Phytophage is difficult to control due to development of insecticide resistance and presence of different growth stages at the same time in summer. Therefore, the research aim was to identify the most effective insecticides with various modes of action that restrain the number and development of pear psylla nymphs. The research tasks were to clarify biological features of pear psylla development and to determine effectiveness of insecticides with various modes of action in controlling P. pyri L. population. Pear psylla development in Prikubansky zone of the Krasnodar region was studied and the results were presented. During the research years, the sum of effective temperatures necessary for: start of egg laying was 40 C (at a threshold of 6 C); beginning of larvae hatching was 121122 C; period from egg to imago 300 C. Pest development monitoring showed that the insect has 6 full generations in the growing season. Field experiments were conducted with Leven pear variety in Prikubansky zone, central gardening subzone of the Krasnodar Territory on the basis of genetic collection of North Caucasian Federal Scientific Center of Horticulture, Viticulture, Winemaking in 20212022 to determine biological effectiveness of insecticides. The results revealed that chemicals based on juvenoids and chitin synthesis inhibitors were not inferior in effectiveness to chemical insecticides. The two-year studies showed that the highest effectiveness after a single application of the chemicals Akarb, WDG (250 g/kg fenoxycarb) and Dimilin, WDG (800 g/kg diflubenzuron) was on the 10th day and amounted to 83.391.7 %, which was higher than the effectiveness of the standard.
Whole ecosystem-based approaches are becoming increasingly common in pest management within agricultural systems. These strategies consider all trophic levels and abiotic processes within an ecosystem, including interactions between different factors. This review outlines a whole ecosystem approach to the integrated pest management of pear psyllid (Cacopsylla pyri Linnaeus) within pear (Pyrus communis L.) orchards, focusing on potential disruptions as a result of climate change. Pear psyllid is estimated to cost the UK pear industry £5 million per annum and has a significant economic impact on pear production globally. Pesticide resistance is well documented in psyllids, leading to many growers to rely on biological control using natural enemies during the summer months. In addition, multiple insecticides commonly used in pear psyllid control have been withdrawn from the UK and Europe, emphasising the need for alternative control methods. There is growing concern that climate change could alter trophic interactions and phenological events within agroecosystems. For example, warmer temperatures could lead to earlier pear flowering and pest emergence, as well as faster insect development rates and altered activity levels. If climate change impacts pear psyllid differently to natural enemies, then trophic mismatches could occur, impacting pest populations. This review aims to evaluate current strategies used in C. pyri management, discuss trophic interactions within this agroecosystem and highlight potential changes in the top-down and bottom-up control of C. pyri as a result of climate change. This review provides a recommended approach to pear psyllid management, identifies evidence gaps and outlines areas of future research.
The pear psyllids (Cacopsylla Ossiannilsson; Hemiptera: Psylloidea: Psyllidae) are a taxonomically difficult group of at least 24 species native to the Palaearctic region. One or more species occur in most pear-growing regions, in some cases as invasive introductions. Existing reviews of this group are primarily of taxonomic focus with limited overviews of biology. The earliest biological studies of the pear psyllids centered on a core group of a few western European species. In part, this focus arose because diversity of the pear psyllids was poorly understood. As taxonomic understanding has advanced over the last 3 decades, research has expanded taxonomically. Increasing difficulties in controlling the pear psyllids additionally has contributed to growth in research. Here, we review a now-extensive literature on diversity, biology, and management of the pear psyllids. Three broad observations emerged from this synthesis. First, large gaps in biological understanding of the pear psyllids persist for several geographic faunas, most notably for psyllids of the Eastern Palaearctic region. Second, taxonomic diversity is accompanied by biological diversity. Despite the commonality in host use among the pear psyllids, with each species being limited to development on Pyrus, striking differences exist among species in life cycles, wintering, and other biological traits. Third, many of the tools being used to manage pear psyllids today are in existence because of the long history of basic research which has targeted these pests. These tools include new insecticides of higher selectivity, various cultural and horticultural tactics, and practices that conserve natural enemies in orchards.
Overwintering of invertebrates in Central Europe drives the population dynamics in the subsequent seasons and have the direct impact on ecosystem services and biodiversity conservation. The objective of this study was to investigate the small- and middle-scale spatial and temporal distribution of overwintering invertebrates in the fallen leaves in three fruit orchards. The early and late winter distributions of several arthropod taxa were studied in fallen leaves in apple, pear, and cherry orchards in relation to several environmental variables. In the predefined areas (1 x 1 m) samples of fallen leaves were collected in the winter 2018/2019 and 2019/2020. Data from an area of 168 m ² was used for evaluation. A total of 1281 invertebrate individuals were collected. The most abundant were spiders with 787 specimens. Samples also comprised 17 other invertebrate species or higher taxonomic categories, 10 of which were considered as beneficial, four as pests, and three were unclassified. Spiders were analysed more precisely due to their dominance and their possible importance in plant protection. We demonstrate for the first time that fallen leaves in fruit orchards offer a suitable overwintering microhabitat for predatory arthropods and comprehensively evaluate the overwintering arthropod assemblage in relation to several ecological and environmental variables.
Plantations of non-native trees for commercial use are common practice in Europe. They are known to have severe ecological impacts on arthropod fauna by altering microclimatic conditions and reducing microhabitat diversity. However, the effect of plantation tree species on winter-active fauna is relatively unknown. Spiders are a diverse predatory arthropod taxon with strong effect on their prey populations. The composition of spider communities sensitively indicates changes in habitat structure. We established 40 sampling sites in five non-native pine and five native poplar plantations and collected spiders with pitfall traps for two winters in the Southern part of Hungary. We assessed the average height of vegetation and percentage cover of leaf litter, mosses, herbaceous vegetation, and shrubs to characterize habitat structure. We found species richness and activity density of spiders in the non-native compared to the native plantations, presumably due to the more temperate microclimate in pine than in poplar plantations. However, there was no significant effect of habitat structure and its interaction with forest type on species richness and activity density of spiders. Species composition of non-native and native plantation forests differed significantly. Furthermore, we identified six characteristic spider species of non-native plantations with preference for relatively moist habitat conditions. The single characteristic species, (Agroeca cuprea Menge, 1873) for the native plantations preferred dry and partly shaded habitats. We conclude that the effect of microclimatic differences and prey availability presumably overrides the effect of habitat structure on winter-active spiders.
Spiders are among the most abundant natural enemies in many agroecosystems. However, their role in biological control is still questionable because, as generalist predators, they may not only reduce pest populations but may also disrupt the biocontrol exerted by other natural enemies. This thesis focuses of improvement of spiders’ biocontrol potential in pome fruit orchards. A special focus was devoted to the system occurring in the pear orchards during winter, involving the winter-active spiders Philodromus spp. (Philodromidae) and Anyphaena accentuata (Anyphaenidae) and a psyllid pest Cacopsylla pyri, which belongs to the most serious pest of pears in Europe. This dissertation thesis consists of six studies. The first study investigates the efficiency of various hunting strategies of spiders capturing different prey types. In general, spiders effectively capture prey like hemipterans and dipterans, but the different hunting strategies differ in their efficiency with respect to capturing specific prey type. The rest of the studies focus on trophic niches of philodromids and Anyphaena, intraguild predation (IGP) among the spiders, and the spiders’ ability to suppress psylla during winter and early spring. Winter-active spiders mostly prefer preying on pests in orchards and significantly reduce the population of C. pyri during winter and early spring. However, their efficiency is reduced by IGP. IGP can be reduced by installation of corrugated cardboard bands around pear trees that provide refuges for small spiders. The efficiency of psylla suppression highly depends on the behavioral composition of the philodromid populations and the ratio between abundances of philodromids and the Dictyna sp. spiders. Aggressive philodromids kill more pests, are non-choosy, and do not prefer either psylla or Dictyna. Timid philodromids kill fewer pests, are choosy, and prefer psylla to Dictyna. The aggressive/non-choosy philodromids are more effective in psylla suppression when the Philodromus to Dictyna abundance ratio is high, while the timid/choosy philodromids are more effective when the ratio is low. The results of this thesis show that communities of the winter-active spiders can serve as highly efficient biocontrol agents in orchards.
The present study was designed to record the effect of λ-cyhalothrin, Bifenthrin, and Glyphosate on the mortality, avoidance behavior, foraging activity, and activity of Acetylcholine esterase (AChE) and Carboxylesterase (CarE) in Neoscona theisi (Walckenaer, 1841). Highest mortality (70%) in N. theisi was recorded against λ-cyhalothrin. However, Glyphosate was found to be least toxic. Spider spent less time on insecticides/herbicide-treated surfaces. Insecticides/herbicide-treated N. theisi consumed less prey than untreated control spiders. Similarly, when N. theisi were offered insecticide/herbicide-treated prey, they consumed significantly less. Increased AChE and CarE activities were recorded in insecticides/herbicide-treated spiders as compared to control group. Total protein contents were less in insecticides/herbicide-treated spiders than control group. The results revealed that λ-cyhalothrin is more harmful to spiders as compared to Bifenthrin and Glyphosate. It is suggested that the effect of all pesticides used in agro-ecosystem on beneficial insects should be evaluated before using them in the fields.
The book is focused on regression models, specifically generalized linear models (GLM). It is intended for biology students and scholars and requires only basic statistical knowledge, gained e.g. in an one-semester course of biostatistics. The text includes a minimum of statistical theory and eighteen real examples from biology. Each example consists of a description of a problem, aims, development of statistical models, analysis, diagnosis, and conclusion. Analysis is performed using R. All examples were selected to show a variety of problems and potential pitfalls that can arise during statistical analysis. At the same time, examples show how to think about the statistical models and how to use them. Analyses can be practised by readers using the data that come with the book.
Available at http://www.muni.cz/press/books/pekar_en?lang=en
True predators are characterised by capturing a number of prey items during their lifetime and by being generalists. Some true predators are facultative specialists, but very few species are stenophagous specialists that catch only a few closely related prey types. A monophagous true predator that would exploit a single prey species has not been discovered yet. Representatives of the spider family Ammoxenidae have been reported to have evolved to only catch termites. Here we tested the hypothesis that Ammoxenus amphalodes is a monophagous termite-eater capturing only Hodotermes mossambicus. We studied the trophic niche of A. amphalodes by means of molecular analysis of the gut contents using Next Generation Sequencing. We investigated their willingness to accept alternative prey and observed their specific predatory behaviour and prey capture efficiency. We found all of the 1.4 million sequences were H. mossambicus. In the laboratory A. amphalodes did not accept any other prey, including other termite species. The spiders attacked the lateral side of the thorax of termites and immobilised them within 1 min. The paralysis efficiency was independent of predator:prey size ratio. The results strongly indicate that A. amphalodes is a monophagous prey specialist, specifically adapted to feed on H. mossambicus.
Accurate characterization of predator-prey linkages in agroecosystems is important prior to the implementation of conservation biological programs. The Russian wheat aphid, Diuraphis noxia (Hemiptera: Aphididae), is a significant pest of wheat and barley in the United States. This research utilized molecular gut-content analysis as a minimally disruptive technique to characterize the trophic connectivity between two spider species, Tetragnatha laboriosa Hentz 1850 and Pardosa sternalis (Thorell 1877), and D. noxia. We describe the development of species-specific primers that amplify a 227 bp fragment of D. noxia COI mtDNA to identify the frequency of predation under varying aphid densities and developmental stages of winter wheat. We tested the hypotheses that predation rates on D. noxia would be highest for both spider species at the greatest aphid infestation level in the aphid-resistant wheat cultivar plots and that densities of T. laboriosa would be highest at the highest aphid infestation level in the aphid-resistant cultivars. Despite short detection periods of prey DNA in the laboratory, 32% and 48% of field-collected T. laboriosa and P. sternalis spiders screened positive for D. noxia DNA, respectively. T. laboriosa densities were highest at the highest aphid infestation level. Aphid-resistant wheat cultivars did not impact predation rates or densities. Additionally, P. sternalis predation on D. noxia increased with increasing aphid infestation levels. Given the high predation rates on D. noxia and their association with increased aphid densities, both spider species represent important natural enemies within wheat agroecosystems, and further research is required to quantify their impact on aphid populations.
An analysis of 29 faunal surveys of spiders found in nine field crops in the United States indicates the presence of 614 species in 192 genera and 26 families . These species represent 19% of the ca . 3311 species occurring in North America . These differences may be attributable to guild characteristics associated with dispersal and ability to survive in disturbed habitats . The 42 most frequently occurring spider species were considered in detail and demonstrated that the active wandering guild comprised the largest portion (45%) of this group . Orb-web (21%), sheet-web (19%), ambush-wander (10%), and web-matrix (5%) spiders represented other guilds . The most frequently occurring species in field crops were Oxyopes salticusHentz (Oxyopidae), Phidippus audax (Hentz) (Salticidae), and Tetragnatha laboriosaHentz (Araneidae) . These three species are prime candidates for augmentation and conservation in field crops or in adjacent habitats as part of a strategy to increase predation on crop pests .
Predators of apple and pear pests in northern and central Europe and their use as biological control agents are reviewed. Many natural enemy species are specialized feeders and are able to respond to the population dynamics of particular pest species. The most oustandingly successful example of this is the use of phytoseiid mites, particularly Typhlodromus pyri , against phytophagous pest mites in apple. This mite management strategy is now widespread throughout European apple growing regions. Another example is the use of Anthocoris nemoralis against pear psyllids, Cacopsylla pyricola and C. pyri . Several groups of naturally occurring polyphagous predators, such as chrysopids, coccinellids, syrphids and spiders, also prey on a number of pest species in orchards, contributing generally to the reduction in pest populations. However, they are unlikely alone to prevent pest damage fully and reliably. In seeking biological control opportunities for a particular pest, these polyphagous natural enemies are unlikely to be a high priority. An exception, due to its abundance in orchards, is the common earwig, Forficula auricularia , although this predator may also cause some fruit injury. Another option to consider when reviewing possibilities for biological control in orchards is the introduction of biological control agents. The success rate of this approach, using arthropod predators to control pests of field crops, has been generally poor. Furthermore, mass production methods for predators are likely to be difficult and very costly. The biological supplies industry is constantly seeking culture techniques, largely for arthropod biological control agents of pests of protected crops. It is possible that some future advance may be relevant to orchards, though currently available predators do not appear promising. A careful economic appraisal of the feasibility of use of any potential biological control agent would be prudent before embarking on research.
Accurate characterization of predator-prey linkages in agroecosystems is important prior to the implementation of conservation biological programs. The Russian wheat aphid, Diuraphis noxia (Hemiptera, Aphididae), is a significant pest of wheat and barley in the United States. This research utilized molecular gut-content analysis as a minimally disruptive technique to characterize the trophic connectivity between two spider species, Tetragnatha laboriosa Hentz 1850 and Pardosa sternalis (Thorell 1877), and D. noxia. We describe the development of species-specific primers that amplify a 227 bp fragment of D. noxia COI mtDNA to identify the frequency of predation under varying aphid densities and developmental stages of winter wheat. We tested the hypotheses that predation rates on D. noxia would be highest for both spider species at the greatest aphid infestation level in the aphid-resistant wheat cultivar plots and that densities of T. laboriosa would be highest at the highest aphid infestation level in the aphid-resistant cultivars. Despite short detection periods of prey DNA in the laboratory, 32% and 48% of field-collected T. laboriosa and P. sternalis spiders screened positive for D. noxia DNA, respectively. Additionally, P. sternalis predation on D. noxia increased with increasing aphid infestation levels. Given the high predation rates on D. noxia and their associations with increased aphid densities, both spider species represent important natural enemies within wheat agroecosystems, and further research is required to quantify their impact on aphid populations.
Aphids are major pests in apple orchards, debilitating the crop and spreading disease. We investigated whether early-season predation by canopy spiders may be effectively controlling aphid numbers in three organic orchards. For this purpose, we monitored the aphid population dynamics from the winter eggs to colony stages and compared this to spider abundances and rates of predation on aphids detected by diagnostic polymerase chain reaction. For the latter, we applied existing general aphid primers. We found that spiders ate colony fundatrices and that aphid numbers were negatively related to spider abundance. Spiders were the main active predators within the orchards when the first colony fundatrices were present, indicating their importance in the early control of aphid populations.
Food webs in nature have multiple, reticulate connections between a diversity of consumers and resources. Such complexity affect web dynamics: it first spreads the direct effects of consumption and productivity throughout the web rather than focusing them at particular 'trophic levels'. Second, consumer densities are often donor controlled with food from across the trophic spectrum, the herbivore and detrital channels, other habitats, life-history omnivory, and even trophic mutualism. Although consumers usually do not affect these resources, increased numbers often allow consumers to depress other resources to levels lower than if donor-controlled resources were absent. We propose that such donor-controlled and "multi-channel" omnivory is a general feature of consumer control and central to fooweb dynamics. This observation is contrary to the normal practice of inferring dynamics by simplifying webs into few linear "trophic levels" as per "green world" theories. Such theories do not accomodate common and dynamically important features of real webs such as the ubiquity of donor control and the importance and dynamics of detritus, omnivory, resources crossing habitats, life history, nutrients(as opposed to energy), pathogens, resources defenses, and trophic symbioses. We conclude that trophic cascades and top-down community regulation as envisioned by trophic-level theories are relatively uncommon in nature.
Abstract Single trophic-level studies of the relationship between biodiversity and ecosystem functioning highlight the importance of mechanisms such as resource partitioning, facilitation, and sampling effect. In a multi-trophic context, trophic interactions such as intraguild predation may also be an important mediator of this relationship. Using a salt-marsh food web, we investigated the interactive effects of predator species richness (one to three species) and trophic composition (strict predators, intraguild predators, or a mixture of the two) on ecosystem functions such as prey suppression and primary production via trophic cascades. We found that the trophic composition of the predator assemblage determined the impact of increasing predator species richness on the occurrence of trophic cascades. In addition, increasing the proportion of intraguild predator species present diminished herbivore suppression and reduced primary productivity. Therefore, trophic composition of the predator assemblage can play an important role in determining the nature of the relationship between predator diversity and ecosystem function.
Stenophagy (narrow diet breadth) represents an extreme of trophic specialization in carnivores, but little is known about the forces driving its evolution. We used spiders, the most diversified group of terrestrial predators, to investigate whether stenophagy (1) promoted diversification; (2) was phylogenetically conserved and evolutionarily derived state; and (3) was determined either by geographical distribution and foraging guild. We used published data on the prey of almost 600 species. Six categories of stenophagy were found: myrmecophagy, araneophagy, lepidopterophagy, termitophagy, dipterophagy, and crustaceophagy. We found that the species diversity of euryphagous genera and families was similar to stenophagous genera and families. At the family level, stenophagy evolved repeatedly and independently. Within families, the basal condition was oligophagy or euryphagy. Most types of stenophagy were clearly derived: myrmecophagy in Zodariidae; lepidopterophagy in Araneidae; dipterophagy in Theridiidae. In contrast, araneophagy was confined to basal and intermediate lineages, suggesting its ancestral condition. The diet breadth of species from the tropics and subtropics was less diverse than species from the temperate zone. Diet breadth was lower in cursorial spiders compared to web-building species. Thus, the evolution of stenophagy in spiders appears to be complex and governed by phylogeny as well as by ecological determinants.
Spiders have been commonly considered as polyphagous predators. For this reason, it has been argued that spiders may not be efficient in controlling pests. However, in recent years it has been demonstrated that they are able to significantly decrease the damage caused by insects to harvest. In this paper we present some preliminary results of a field experiment that has taken place in 2007, in a biological apple orchard at Caraglio (Cuneo, North-Western Italy). The aim of the experiment was to study the potential reduction of the damage caused by Cydia spp. (Lepidoptera: Tortricidae) to apples by increasing the population size of spiders living on trees by offering them additional shelter space through the provision of artificial shelters (polyethylene bark-traps) during wintertime. The spider assemblage was found to be strongly dominated by Anyphaena accentuata (43%), followed by Dictyna arundinacea (20%) and Philodromus spp. (8%). Compared to control, the total number of spiders increased significantly in trees provided with artificial shelter and trees with such device showed lower frequency of damaged apples. Results from this preliminary study suggest that habitat manipulation in apple orchards may increase the population size of bark dwelling spiders and thus increase their potential preying efficiency..
The analysis of food webs and their dynamics facilitates understanding of the mechanistic processes behind community ecology and ecosystem functions. Having accurate techniques for determining dietary ranges and components is critical for this endeavour. While visual analyses and early molecular approaches are highly labour intensive and often lack resolution, recent DNA-based approaches potentially provide more accurate methods for dietary studies. A suite of approaches have been used based on the identification of consumed species by characterization of DNA present in gut or faecal samples. In one approach, a standardized DNA region (DNA barcode) is PCR amplified, amplicons are sequenced and then compared to a reference database for identification. Initially, this involved sequencing clones from PCR products, and studies were limited in scale because of the costs and effort required. The recent development of next generation sequencing (NGS) has made this approach much more powerful, by allowing the direct characterization of dozens of samples with several thousand sequences per PCR product, and has the potential to reveal many consumed species simultaneously (DNA metabarcoding). Continual improvement of NGS technologies, on-going decreases in costs and current massive expansion of reference databases make this approach promising. Here we review the power and pitfalls of NGS diet methods. We present the critical factors to take into account when choosing or designing a suitable barcode. Then, we consider both technical and analytical aspects of NGS diet studies. Finally, we discuss the validation of data accuracy including the viability of producing quantitative data.
The objectives of this work are: (1) to define spider guilds for all extant families worldwide; (2) test if guilds defined at family level are good surrogates of species guilds; (3) compare the taxonomic and guild composition of spider assemblages from different parts of the world; (4) compare the taxonomic and functional diversity of spider assemblages and; (5) relate functional diversity with habitat structure. Data on foraging strategy, prey range, vertical stratification and circadian activity was collected for 108 families. Spider guilds were defined by hierarchical clustering. We searched for inconsistencies between family guild placement and the known guild of each species. Richness and abundance per guild before and after correcting guild placement were compared, as were the proportions of each guild and family between all possible pairs of sites. Functional diversity per site was calculated based on hierarchical clustering. Eight guilds were discriminated: (1) sensing, (2) sheet, (3) space, and (4) orb web weavers; (5) specialists; (6) ambush, (7) ground, and (8) other hunters. Sixteen percent of the species richness corresponding to 11% of all captured individuals was incorrectly attributed to a guild by family surrogacy; however, the correlation of uncorrected vs. corrected guilds was invariably high. The correlation of guild richness or abundances was generally higher than the correlation of family richness or abundances. Functional diversity was not always higher in the tropics than in temperate regions. Families may potentially serve as ecological surrogates for species. Different families may present similar roles in the ecosystems, with replacement of some taxa by other within the same guild. Spiders in tropical regions seem to have higher redundancy of functional roles and/or finer resource partitioning than in temperate regions. Although species and family diversity were higher in the tropics, functional diversity seems to be also influenced by altitude and habitat structure.
Comparative analysis of molecular sequence data is essential for reconstructing the evolutionary histories of species and inferring the nature and extent of selective forces shaping the evolution of genes and species. Here, we announce the release of Molecular Evolutionary Genetics Analysis version 5 (MEGA5), which is a user-friendly software for mining online databases, building sequence alignments and phylogenetic trees, and using methods of evolutionary bioinformatics in basic biology, biomedicine, and evolution. The newest addition in MEGA5 is a collection of maximum likelihood (ML) analyses for inferring evolutionary trees, selecting best-fit substitution models (nucleotide or amino acid), inferring ancestral states and sequences (along with probabilities), and estimating evolutionary rates site-by-site. In computer simulation analyses, ML tree inference algorithms in MEGA5 compared favorably with other software packages in terms of computational efficiency and the accuracy of the estimates of phylogenetic trees, substitution parameters, and rate variation among sites. The MEGA user interface has now been enhanced to be activity driven to make it easier for the use of both beginners and experienced scientists. This version of MEGA is intended for the Windows platform, and it has been configured for effective use on Mac OS X and Linux desktops. It is available free of charge from http://www.megasoftware.net.
Molecular methods have become an important tool for studying feeding interactions under natural conditions. Despite their growing importance, many methodological aspects have not yet been evaluated but need to be considered to fully exploit the potential of this approach. Using feeding experiments with high alpine carabid beetles and lycosid spiders, we investigated how PCR annealing temperature affects prey DNA detection success and how post-PCR visualization methods differ in their sensitivity. Moreover, the replicability of prey DNA detection among individual PCR assays was tested using beetles and spiders that had digested their prey for extended times postfeeding. By screening all predators for three differently sized prey DNA fragments (range 116-612 bp), we found that only in the longest PCR product, a marked decrease in prey detection success occurred. Lowering maximum annealing temperatures by 4 °C resulted in significantly increased prey DNA detection rates in both predator taxa. Among the three post-PCR visualization methods, an eightfold difference in sensitivity was observed. Repeated screening of predators increased the total number of samples scoring positive, although the proportion of samples testing positive did not vary significantly between different PCRs. The present findings demonstrate that assay sensitivity, in combination with other methodological factors, plays a crucial role to obtain robust trophic interaction data. Future work employing molecular prey detection should thus consider and minimize the methodologically induced variation that would also allow for better cross-study comparisons.
The species richness and composition of spider assemblages were investigated in the canopy, herbaceous-layer and at ground level when differently treated with pesticide and in abandoned apple and
pear orchards in the Carpathian Basin. Furthermore attention was paid to the bark-inhabiting spider fauna.
Altogether 20,283 individuals were collected belonging to 21 families; 165 spider species have been identified to species level and further nine spider taxa were determined up to generic level. More than 20%
of the Hungarian spider fauna was represented in the orchards. In the canopies, 103 species were found in apple orchards and 70 species in pear orchards. The similarity (Jaccard index) between apple and pear in the canopy is 45%. The species richness in each orchard varied between 22 and 56 species. In the herbaceous layer, 66 species were found in apple orchards and 43 species in pear orchards.
Most of the species belonged to the families Araneidae, Salticidae, Thomisidae, Theridiidae. Species of hunting spiders were represented by 55%, web-building spiders by 45% of the entire fauna.
The canopy and the herbaceous layer inhabiting fauna overlapped. Out of the 76 herbaceouslayer inhabiting species, 59 occurred also in the canopy. The similarity (Jaccard index) in species composition between the canopy and the herbaceous-layer is 45%.
The most widely occurring species in orchard canopies in decreasing order were: Philodromus cespitum, Theridion impressum, Theridion pinastri, Oxyopes heterophthalmus, Araniella opistographa; on the bark: Philodromus cespitum, Xysticus spp. (lanio, cristatus), Drassodes lapidosus, Theridion pinastri, Clubiona marmorata; in the herbaceous-layer: Xysticus spp. (cristatus, ulmi), Oxyopes heterophthalmus, Pisaura mirabilis, Mangora acalypha, Araneus diadematus; on the ground-level: Xysticus kochi, Titanoeca schineri, Pardosa agrestis, Alopecosa sulzeri, Harpactea rubicunda. This species could play a role in the natural control of orchard pests in IPM systems in the Carpathian Basin.
Three species collected in the canopy of apple and pear orchards, Enoplognatha latimana, Philodromus longipalpis and Euophrys monticola were not recorded from Hungary until the present study.
Predatory and parasitoid arthropods occurring on seven species of shrubs surrounding an experimental apple orchard were studied. Spiders represented 35-58% of all arthropods collected; 72 spider species were found, belonging to the Araneidae (with Metidae), Linyphiidae, Tetragnathidae, Agelenidae, Anyphaenidae, Dictynidae, Theridiidae, Clubionidae, Thomisidae, Salticidae and Lycosidae. Greatest numbers of spiders were usually gound on Crataegus sp., Euonymus europaea and Caragana sp. Araniella cucurbitina and Theridion varians occurred every year on all examined shrubs and jointly accounted for >34% of all collected spiders. -from Authors
It is, indeed, an amazing fact that in the cold months of winter an ectothermic animal, such as a spider, can move about and even feed. In fact, biologists usually stay indoors at this time before their fires and rarely venture outside themselves. So only a few hardy souls have been able to observe this phenomenon of winter activity by spiders. This chapter discusses the “why”, “how”, “what” and “where” of feeding ecology of winter-active spiders, together with the actual microclimatic conditions encountered and the physiological and ecological implications of this feeding.
We can identify agricultural systems in which spiders might best be applied in pest suppression from study of the mechanisms by which spider populations influence prey in natural ecosystems. Theory predicts that prey control is achieved through the development of a stable interaction between predator and prey populations. Two models have been applied to predator control of prey, limit cycle and equilibrium point or focal control. Limit cycle control is exerted on a prey species population by a predator species that tracks the densities of its prey. Although the limit cycle approach is commonly applied to pest control situations, the long life cycles and generalist feeding habits of spiders limit their abilities to exhibit density-dependent tracking of their prey. Crops with short growing seasons and species-depauperate systems are the best candidates for limit cycle influences of spiders on prey. Spider populations that exhibit an uneven age-structure and have strong migratory/aggregational tendencies would offer the greatest pest suppression in these simple systems. Equilibrium point/focus control involves the limiting effects of an assemblage of polyphagous feeders on an assemblage of prey species. Spiders fit this model to a greater extent than they do a limit cycle model of prey control. Agricultural systems that conserve spider densities and species representation through minimal chemical application and the maintenance of ground cover are good candidates for equilibrium point control of prey by spiders. It is also important to recognize that many success stories in agroecosystems do not involve stable interactions between predator and prey populations. Indirect effects (e.g., the cessation of feeding in the presence of a predator) and superfluous killing of prey are two factors that augment the influence of spiders on targeted insect populations.
The latest version of ImageJ, ImageJ 1.31, has released by Wayne Rasband of the Research Services Branch, National Institute of Mental Health, Bethesada, Md. ImageJ holds a unique position because it not only is in the public domain, but also runs on any operating system. It can read most of the common and important formats used in the field of biomedical imaging. The program supports all common image manipulations, including reading and writing of image files, and operations on individual pixels, image regions, whole images and volumes. The simple ImageJ macro acquire an image every 10 seconds and stores and stores it in sequence. ImageJ has attracted a varied and dedicated group of users because it is free and expandable, and can operate on any platform.
Determining the phenological and diel concurrence of potentially overlapping predator guilds in a given system provides a gauge of the potential prevalence and importance of synergistic prey suppression. The phenology of pea, aphids (Acyrthosiphon pisum) and ground- and foliar-foraging predators was determined through a combination of pitfall and sweep-net sampling in alfalfa. These results revealed diverse guilds of ground-and foliar-foraging predators with a high degree of phenological overlap among individual species. One of the most common ground-foraging predators, Harpalus pennsylvanicus, was found to be significantly more active at night, but also to maintain moderate activity levels during the day. When tested individually in simple arenas with full access to aphids, the aphid-consumption rates of five common ground-foraging predators (H. aeneus, H. pennsylvanicus, Amara familiaris, A. octopunctatum, and Philonthus spp.) were not significantly different from that of Coccinella septempunctata, a foliar-foraging predator that is held to be one of the most important aphid consumers in alfalfa. Thus, both the seasonal occurrence and daily activity levels of these two aphid predator guilds overlap, and the ground-foraging predators, which are often overlooked as sources of aphid predation, were shown to be effective aphid consumers. Three key elements emerge from the alfalfa-aphid-predator system as general predictors of the probability for the synergistic predation on pests by members of a predator complex: (1) synchrony of predator species in the complex, (2) predator-induced escape behavior of prey resulting in habitat switching and encounter with a new predator guild, and (3) minimal negative interaction (intraguild predation or interference) between the predator species. These elements can aid in identifying systems where the conservation or augmentation of ground-foraging predators or other interactive predator guilds will be most effective.
We examined density dependence in population attributes and community impact of a generalist predator by experimentally mimicking natural variation in initial cohort densities produced by synchronous egg hatch in Mantis religiosa (Mantodea: Mantidae). Mantid cohorts within the normal range of emergence from a single egg mass were established in a replicated, well-controlled open field experiment. On the scale of the progeny from a single female, density-dependent food limitation caused mortality and ontogenetic asynchrony to increase with increasing density. All cohorts converged to a common level of abundance and biomass because both development rate and population size declined with increasing initial density. Numbers and biomass of other arthropods generally declined with increasing initial density of mantids, although there were both positive and negative effects on different taxa. The abundance of hemipterans (almost exclusively herbivorous mirids) increased in the presence of mantids; this was an indirect effect as large in magnitude as any of the direct reductions in abundance of other taxa. Per capita interaction strengths of mantids on most taxa generally were weak except for the strong positive interaction with hemipterans. In spite of different mantid development rates among treatments, predator load (proportion of arthropod biomass present as predators) for all three treatments, attributable mainly to mantid biomass, converged to approximately five times control level by the end of the experiment. The differences in predator loads between control and treatment plots thus may represent different levels of predator saturation: one for control plots, where predator load was constant over time and in which generalists contributed relatively little to predator biomass, and a higher one for treatment plots, in which generalists comprised the bulk of predator biomass. Predator load may therefore be an indicator of the relative importance of generalist vs. specialist predators in terrestrial arthropod assemblages.
A number of different generalist (polyphagous) predators occur in agroecosystems. Yet their biocontrol potential has been little investigated in detail. Philodromus species (Philodromidae) belong to the dominant spider species occurring in commercial orchards. We studied in detail the trophic functional traits of Philodromus albidus, Philodromus aureolus, and Philodromus cespitum (Philodromidae) by means of (1) the analysis of natural prey; and (2) experiments on acceptance of a variety of prey taxa. We found that the three philodromids are euryphagous. We classified prey species into three categories according to their function in the orchard: beneficial species, indifferent species, and pests. Philodromid spiders captured mostly other spiders in the field because spiders were most available. As concerns pests, the philodromids preyed mostly on Brachycera and Sternorrhyncha. They selected Acari and Brachycera. Indifferent species, such as Collembola and Nematocera, were also highly selected. In the laboratory, philodromids accepted mostly pests, such as lepidopterans, brachycerans, and aphids, while other spiders were accepted the least. The three philodromids have differentiated trophic niches with respect to prey size not only in the adult stage but throughout their ontogenetic development: P. albidus utilized smaller prey than the other two species. We conclude that the philodromids have a potential as biocontrol agents because they prey mostly on pests but their predation pressure is reduced due to higher selectivity for the indifferent fauna.
The role of generalist predators in pest control has been neglected because generalists are not able to track pest populations. Generalist predators are suggested to be important in spring before specialist predators become active.
Here, we show that some generalist predators are important even during winter, when the majority of arthropod pests and their enemies are dormant. We quantified the role of winter‐active generalist predators on the suppression of pear psylla during winter using a discrete nonlinear model of an intraguild predation system.
To parameterize our model, we conducted a series of experiments on (i) functional responses, (ii) prey preferences and (iii) ontogenetic development and made observations on the population densities of spiders and potential prey. We ran the model for different winter scenarios, that is, for very cold and very warm winters.
Synthesis and applications . We found that winter‐active predators considerably suppressed the pear psylla population. Predators exerted a stronger effect in a warmer winter than in a colder one. Orchard growers thus should avoid use of non‐selective pesticides during this period and instead aim to support the community of generalist predators. Our results suggest more attention should be given to encouraging generalist predator populations in other systems, even in periods when crops are not producing.
At least 54 species of spiders are winter-active in central, southern Canada, displaying phenologies which seem to be 42.6% stenochronous, 38.9% eurychronous and 14.8% winter-mature, with juveniles and adult stages overwintering. The cool climate of Manitoba appears to have prolonged the duration of the life cycles of some spiders. The family composition during the winter months is 34.6% erigo-nines (mostly represented by Ceraticelus laetus and Sisicus sp.), 13.8% clubionids (Agroeca or~mta), 13.5% lycosids, 11.1% linyphiines (Centroraerus syh,aticus), 8.8% thomisids (juveniles of Xysticus), 6.1% theridiids (Robertus arctieus), and 12.0% other families.
Predators appear to be less frequently specialised (i.e. adapted to restricted diet) on their prey than herbivores, parasites or parasitoids. Here, we critically evaluate contemporary evolutionary hypotheses that might be used to explain the evolution of specialised foraging in predators. We propose a unifying concept within which we define four types of trophic categories using ecological (diet breadth) and evolutionary (degree of adaptations) contexts. We use data on spiders (Araneae), the most diversified order of terrestrial predators, to assess applicability of frameworks and evolutionary concepts related to trophic specialisation. The majority of spider species are euryphagous but a few have a restricted prey range, i.e. they are stenophagous. We provide a detailed overview of specialisation on different prey types, namely spiders, crustaceans, moths, dipterans, ants, and termites. We also review the available evidence for trophic adaptations, classified into four categories: behavioural, morphological, venomic and metabolic. Finally, we discuss the ecological and evolutionary implications of trophic specialisation and propose avenues for future research.
Predicting whether a predator is capable of affecting the dynamics of a prey species in the field implies the analysis of the complete diet of the predator, not simply rates of predation on a target taxon. Here, we employed the Ion Torrent next-generation sequencing technology to investigate the diet of a generalist arthropod predator. A complete dietary analysis requires the use of general primers, but these will also amplify the predator unless suppressed using a blocking probe. However, blocking probes can potentially block other species, particularly if they are phylogenetically close. Here, we aimed to demonstrate that enough prey sequence could be obtained without blocking probes. In communities with many predators, this approach obviates the need to design and test numerous blocking primers, thus making analysis of complex community food webs a viable proposition. We applied this approach to the analysis of predation by the linyphiid spider Oedothorax fuscus in an arable field. We obtained over two million raw reads. After discarding the low-quality and predator reads, the libraries still contained over 61 000 prey reads (3% of the raw reads; 6% of reads passing quality control). The libraries were rich in Collembola, Lepidoptera, Diptera and Nematoda. They also contained sequences derived from several spider species and from horticultural pests (aphids). Oedothorax fuscus is common in UK cereal fields, and the results showed that it is exploiting a wide range of prey. Next-generation sequencing using general primers but without blocking probes provided ample sequences for analysis of the prey range of this spider and proved to be a simple and inexpensive approach.
The effects of sprays of DDT, azinphos-methyl, and Ryania applied to a pear orchard on population densities of insect predators of Psylla pyricola Förster were assessed. The P . pyricola in the orchard were naturally tolerant to DDT and Ryania and highly resistant to azinphos-methyl. DDT eliminated or severely reduced numbers of Deraeocoris brevis piceatus Knight, D . fasciolus Knight, Diaphnocoris provancheri (Burque), and Campylomma verbasci (Meyer). Chrysopa carnea Stephens and C . oculata Say were moderately reduced. Anthocoris antevolens (White) and A . melanocerus Reuter were highly tolerant to DDT. Azinphos-methyl severely reduced numbers of A . antevolens , A . melanocerus , C . verbasci , and D . provancheri . C . carnea and C . oculata were moderately reduced. D . brevis piceatus and D . fasciolus were tolerant to azinphos-methyl. Ryania severely reduced numbers of A . antevolens , A . melanocerus , and C . verbasci ; moderately reduced D . provancheri ; and did not affect D . brevis piceatus , D . fasciolus , C . carnea , or C . oculata .
In the DDT-treated plots the relative densities of Anthocoris spp. approximately doubled compared with the untreated plots. This was probably due to removal of competition for food by other predator species. Large increases ill the relative densities of Deraeocoris spp. were also observed in the Ryania treatments, probably for similar reasons. Significant increases in the P . pyricola populations in response to removal of predation pressure by the insecticide treatments occurred in the DDT and azinphos-methyl plots bur not in the Ryania plots.
Determining the phenological and diel concurrence of potentially overlapping predator guilds in a given system provides a gauge of the potential prevalence and importance of synergistic prey suppression. The phenology of pea aphids (Acyrthosiphon pisum) and ground- and foliar-foraging predators was determined through a combination of pitfall and sweep-net sampling in alfalfa. These results revealed diverse guilds of ground- and foliar-foraging predators with a high degree of phenological overlap among individual species. One of the most common ground-foraging predators, Harpalus pennsylvanicus, was found to be significantly more active at night, but also to maintain moderate activity levels during the day. When tested individually in simple arenas with full access to aphids, the aphid-consumption rates of five common ground-foraging predators (H. aeneus, H. pennsylvanicus, Amara familiaris, A. octopunctatum, and Philonthus spp.) were not significantly different from that of Coccinella septempunctata, a foliar-foraging predator that is held to be one of the most important aphid consumers in alfalfa. Thus, both the seasonal occurrence and daily activity levels of these two aphid predator guilds overlap, and the ground-foraging predators, which are often overlooked as sources of aphid predation, were shown to be effective aphid consumers. Three key elements emerge from the alfalfa-aphid-predator system as general predictors of the probability for the synergistic predation on pests by members of a predator complex: (1) synchrony of predator species in the complex, (2) predator-induced escape behavior of prey resulting in habitat switching and encounter with a new predator guild, and (3) minimal negative interaction (intraguild predation or interference) between the predator species. These elements can aid in identifying systems where the conservation or augmentation of ground-foraging predators or other interactive predator guilds will be most effective.
Herbivore population dynamics are governed both by bottom-up (plant-mediated) and by top-down (natural enemy-mediated) processes, with the potential for interaction between them. Pear psylla (Cacopsylla pyricola Foërster) is a phytophagous pest in pear orchards. Pear psylla is commonly attacked by several different natural enemies, but it may escape control, especially if fertilizer additions and new shoot production are not carefully managed. We tested the hypothesis that plant quality mediates the efficacy of an important natural enemy of pear psylla, Anthocoris nemoralis. One year-old caged Bartlett pear trees were fertilized at either low (5mM N) or high (20mM N) levels of nitrogen, then either psylla or psylla and Anthocoris were added to each tree. We measured plant growth, psylla population size, and Anthocoris establishment to determine effects of fertilizer and predation on psylla population dynamics. Trees receiving more N were taller, had longer total branches, a greater total number of leaves, and higher leaf nitrogen content. Psylla populations were also larger in the high N treatment. Anthocoris establishment and reproduction was positively related to the density of psylla at the time predators were added. And although psylla densities were, over-all, lower on trees where Anthocoris was present, the level to which Anthocoris suppressed psylla was not significantly affected by fertilizer level. These results indicate that the efficacy of this predator is not strongly mediated by plant quality, at least at the local (i.e. tree) scale. Minimizing fertilizer additions to the minimum level required for proper fruit set is likely to be an important feature of successful pear psylla biocontrol programs.
Overwintering of spiders was studied by means of cardboard trap bands in two different orchards in the Czech Republic, an apple under integrated pest management (in 1993) and an abandoned pear (in 1995). Twenty-seven species of spiders were found to overwinter on tree trunks. The overwintering composition was not very similar to the composition of arboreal spiders detected during spring and summer by beating tree branches. For example, Clubiona specimens occur on ground and canopy in summer but prefer tree trunks to pass winter. Except Clubionidae, three other families, Philodromidae, Theridiidae and Dictynidae, predominated in trap bands. The two study orchards differed in species composition of overwintering spiders as a result of the orchard type (commercial versus abandoned), temporal variation, and the bark structure (rough in pear and smooth in apple). The commercial apple orchard was predominated by small insecticide-tolerant spiders, Theridiidae and Dictynidae, whereas the abandoned pear orchard was dominated by large susceptible species of Clubionidae and Philodromidae. Installation of cardboard bands on young trees with smooth bark may significantly support overwintering of spiders. Distribution of spiders among trap bands of the IPM orchard showed a clumped pattern. It appeared that populations under pressure are spatially distributed. A significant negative correlation was observed between large spiders (Philodromidae) and small ones (Theridiidae and Dictynidae) resulting presumably from interspecific predation. Non-linear models were fitted to these relationships. The relationship between Philodromidae:Clubionidae, Clubionidae:Theridiidae, and Clubionidae:Dictynidae could not be described by correlation. Thus, it is concluded that Clubionidae do not interact with other spiders at overwintering sites.
Anyphaena accentuata and Philodromus spp. Are cold adapter and winter aktive spider species.Their predation aktivity was investigace dat constant temperatures between –4 and 30C. The lower temperature threshold for Anyphaena was –3.7C, while that of Philodromus was –1.2C. At 1C the latency to capture and prey consumption was significantly porter in Anyphaena than in Philodromus. The capture rate increased with temperature and was maximal at 15C in Anyphaena and at 30C in Philodromus. At 30C, the latency to the capture was significantly porter in Philodromus than in Anyphaena whose mortality significantly increased.
We extend detection of arthropod predator gut contents by polymerase chain reaction (PCR), heretofore restricted to insect predators, to spiders. Single individuals of the corn lead aphid, Rhopalosiphum maidis, were detected in the guts of spiderlings of Oxyopes salticus up to 12 h after feeding; individuals of the congeneric bird cherry oat aphid, R. padi, were not detected. Unfed O. salticus and Misumenops sp. were also negative.
Cardboard bands were placed on pear and apple trees at each of three sites to act as overwintering shelters for spiders. Bands were placed on the trees in late August, at three heights on the tree. One-third of the bands was collected in January to determine what taxa of spiders overwintered in the shelters. The remaining bands at each site were collected and replaced at weekly intervals between late August and early December to monitor phenology of movement into the shelters. More than 2,900 spiders in 10 families were recovered from the winter-collected set of bands. Spiders were collected from all three sampling heights in the trees. The majority of spiders were juveniles, although adults of some Salticidae [especially Pelegrina aeneola (Curtis) and Phanias sp.] were fairly common. The dominant families were Philodromidae (primarily Philodromus spp.) and Salticidae (primarily P. aeneola), comprising 66 and 28%, respectively, of the total specimens. In the weekly collections, >5,600 bands were sampled during the study producing >6,000 spiders represented by 12 families and 30 identified genera. Dominant taxa in the weekly collected bands included Philodromus cespitum (Walckenaer), P. aeneola, Xysticus spp. (Thomisidae), Sassacus papenhoei Peckham and Peckham (Salticidae), Phidippus spp. (Salticidae), and Anyphaena pacifica Banks (Anyphaenidae). Of these taxa, Xysticus spp., S. papenhoei, and A. pacifica were very uncommon in the winter-collected bands, and we infer from these results that these spiders used the bands as temporary refuges only, and overwintered elsewhere. Data obtained from the weekly collected bands suggested that Philodromus spp., Dictyna spp., P. aeneola, and Cheiracanthium mildei L. Koch entered overwintering shelters during the interval between mid-October and mid- to late November. Pear and apple blocks at the same site were more similar in community composition than a common crop species at two different sites. More spiders were recovered from bands placed in the unmanaged and organically managed orchards than from apple and pear blocks that received insecticides during the growing season.
Abramoff, M.D., Magelhaes, P.J., Ram, S.J. "Image Processing with ImageJ". Biophotonics International, volume 11, issue 7, pp. 36-42, 2004.
Molecular analysis of predation, through polymerase chain reaction amplification of prey remains within the faeces or digestive systems of predators, is a rapidly growing field, impeded by a lack of readily accessible advice on best practice. Here, we review the techniques used to date and provide guidelines accessible to those new to this field or from a different molecular biology background. Optimization begins with field collection, sample preservation, predator dissection and DNA extraction techniques, all designed to ensure good quality, uncontaminated DNA from semidigested samples. The advantages of nuclear vs. mitochondrial DNA as primer targets are reviewed, along with choice of genes and advice on primer design to maximize specificity and detection periods following ingestion of the prey by the predators. Primer and assay optimization are discussed, including cross-amplification tests and calibratory feeding experiments. Once primers have been made, the screening of field samples must guard against (through appropriate controls) cross contamination. Multiplex polymerase chain reactions provide a means of screening for many different species simultaneously. We discuss visualization of amplicons on gels, with and without incorporation of fluorescent primers. In more specialized areas, we examine the utility of temperature and denaturing gradient gel electrophoresis to examine responses of predators to prey diversity, and review the potential of quantitative polymerase chain reaction systems to quantify predation. Alternative routes by which prey DNA might get into the guts of a predator (scavenging, secondary predation) are highlighted. We look ahead to new technologies, including microarrays and pyrosequencing, which might one day be applied to this field.
In conservation biological control (CBC), we attempt to reduce pest problems by increasing the abundance and diversity of the natural enemy community. However, rather than consistently strengthening herbivore suppression, studies show that the conservation of natural enemy species richness sometimes weakens, or has no affect, on biological control. Evidence is mounting that this idiosyncratic mix of positive, negative, and neutral effects of enemy diversity is caused by niche complementarity, intraguild predation, and functional redundancy, respectively. While the balance of evidence suggests that the conservation of natural enemy diversity and biological control are compatible goals, CBC practitioners cannot ignore the fact that conserving intraguild predators can sometimes disrupt biological control. Recent studies have made important progress toward identifying the traits of enemies and their prey that promote intraguild predation, functional redundancy, and niche complementarity. However, intraguild predation has received more attention than niche complementarity, and more theoretical and empirical work is needed rectify this asymmetry. We suggest that a continued focus on natural enemy functional traits, particularly those that are expressed at larger spatiotemporal scales, will increase our ability to identify the “right” kind of diversity and may ultimately improve the practice of conservation biological control.
Detection of prey DNA-remains in arthropod predators by polymerase chain reaction (PCR) is useful when investigating food webs. In this study we estimated how long after a feeding event it was possible to detect mitochondrial COII DNA (331 bp) from an important aphid pest, Rhopalosiphum padi (Homoptera: Aphididae), in spiders of the genus Pardosa (Araneae: Lycosidae). Following laboratory evaluations we tested spiders collected in spring-sown cereals for aphid predation during two seasons. Aphids were digested rapidly in laboratory-fed predators and the time point when prey DNA could be amplified from 50% of the spiders was estimated to be 3.7 h. A total of 372 field- collected predators were analyzed by PCR and despite low aphid densities many spiders (26% in 2004 and 19% in 2005) tested positive for R. padi, indicating consumption of at least one aphid within a few hours before capture. The percentage of spiders that tested positive for R. padi DNA varied considerably between fields and logistic regression analysis revealed that the probability of detecting aphid DNA was significantly influenced by location and year. We conclude that Pardosa spiders, under certain conditions, frequently feed on R. padi and deserve special attention in conservation biological control.
We studied whether there si intraguild predation among overwintering invertebrates in bark traps installed on apple trees. We found that 86% of the overwintering invertebrates in traps were predators, which were dominated by spiders (72%) of different guilds and different body sizes. Spiders had spatially segregated in the traps so that smaller specimens hid in an interstitial space that was inaccessible to larger specimens. Spiders of the bark-dwelling guild, Anyphaena and Philodromus, are winter-active and can prey on other smaller spiders. Analysis of their abundance in traps indicated a negative relationship between Anyphaena and Philodromus or other spiders. Inspection of traps during winter revealed an influx of spider specimens confirming their winter-activity. In a semi-field experiment, where overwintering in cardboard bands was studied under controlled conditions, we observed mortality of both winter-active Philodromus and Anyphaena spiders due to their interspecific predation. The mortality was affected by their size ratio – larger specimens consumed smaller ones. Presence of alternative prey, theridiid spiders, did not affect their mortalities, but the presence of shelters (interstitial spaces) did. In boards with interstitial spaces smaller spiders suffered lower mortality than in boards without the interstitial spaces. Obtained results suggest that intraguild predation between overwintering spiders can decrease their population density during winter.
In northern Europe at least, extensive knowledge of the systematics and ecology of spiders leads the authors to consider them as a very suitable group for pest limitation and for biodiagnostic purposes. An examination of both the qualitative and quantitative aspects of perdition by spider populations and communities is discussed as well as the evolution of some human factors occurring in agroecosystems that are likely to induce changes in spider predation such as chemical spraying and cultural practices. Studies addressing the recolonisation of agroecosystems by spiders, taking into account their dispersing abilities and habitat selection are summarised, followed by a discussion of the global efficiency of spiders as predators in such environments, the risks associated with their use and how to maximise their efficiency.The bioindicative value of spiders is presented by referring successively to population level and community level. The growth rate or the reproductive rate observed in natural populations can be correlated with the amount of prey ingested in the field. Thus, these parameters give an indirect estimation of the habitat quality. Two specific field experiments are presented to illustrate this ecological concept. Moreover, the role of spiders as indicators of heavy metal pollution (atmospheric or soil pollution) integrated by organisms living close to sources of pollution is discussed by reference to a set of laboratory and field experiments. Due to the close correspondence between the vegetation architecture and the composition of the associated spider community, it is argued (with a list of examples) that fluctuations in the spider community structure allows the bioevaluation of human disturbances. Based on the composition of the spider communities, methods of ecological classifications of natural habitats in several European countries are presented.
Evidence is growing that spiders can be effective biological control agents, particularly assemblages of several species. Other evidence finds that spiders prey on each other and other generalist predators, and as such are of limited value in biological control. Such predatory interactions between species which use similar resources have been dubbed intraguild predation (IGP) due to their potential to modify competition as well as cause direct mortality. IGP interactions can have unexpected effects at other trophic levels, and sometimes result in enhancement of a pest population. In this paper, I review the evidence for intraguild predation interactions involving spiders in natural systems, and other generalist predators in agroecosystems. To date not much research has examined whether such interactions influence spider biological control potential. Some suggestions as to how we might begin to address these issues are presented.
Predation is of great ecological, evolutionary, and behavioural interest. For our present purposes the primary reason for studying it is to determine the role of spiders in supressing pest populations. Research approaches have included laboratory studies of preference, feeding rate, and fitness; direct observation of predation events or accumulations of prey carcasses; gut analysis; and field experiments. Laboratory studies provide some uniquely useful kinds of information but cannot give reliable indications of the "biological control potential" of spiders against a given pest. Direct observations can be powerful; it has provided the best data on dietary range and predation rates in the field. Gut analytical methodsin include the use of radionuclides, electrophoresis, chromatography and serology. Serological techniques are preferred: antibodies can be made specific down to the level of prey stage or instar, and assays are simple, sensitive and reliable. They can determine the relative importnace of different predators species, and may be the most efficinet methods to document predation on eggs. Problems in quantification remain. Field experiments have demonstrated unequivocally that spideres can efectively reduce pest popualtions and the crop damage they cause.
There is a long-standing debate in ecology concerning the relative importance of competition and predation in determining community structure. Recently, a novel twist has been added with the growing recognition that potentially competing species are often engaged in predator-prey interactions. This blend of competition and predation is called intraguild predation (IGP). The study of IGP will lead to a reconsideration of many classical topics, such as niche shifts, species exclusion and cascading interactions in food webs. Theoretical models suggest that a variety of alternative stable states are likely in IGP systems, and that intermediate predators should tend to be superior in exploitative competition. Many field studies support these expectations. IGP is also important in applied ecological problems, such as the conservation of endangered species and fisheries management.
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