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-Mean density (6 SE) of Pardosa sternalis per wheat stage (Zadoks), averaged over wheat varieties and infestation levels, Fort Collins, Colorado, 2008. Columns marked by the same lower case letters are not significantly different.
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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 disr...
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... in 2008. Of these, 28% were male, 51% were immature, and 21% were female. The immatures collected were assumed to be P. sternalis, as no other Pardosa were present at the field site (L.M. Kerzicnik, unpublished data). Wheat stage affected the number of P. sternalis collected (F 4, 277 5 7.43, P , 0.0001) with mean densities highest at Zadoks 40 (Fig. ...
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Citations
... As most generalist predators can forage selectively (Greenstone 1979, Bilde and Toft 1994, Toft 1995, Mayntz et al. 2005, it is not a safe assumption that as a given pest population rises, so does the frequency that the predator population feeds on it. Although many molecular gut content studies report a decoupling of prey availability and the detection of prey DNA in the guts of predators (Kerzicnik et al. 2012, Chapman et al. 2013, Visakorpi et al. 2015, Eitzinger et al. 2019, our findings indicate that the predator community, as a whole, may be positively responding to Dubas bug density changes. ...
The date palm (Phoenix dactylifera L.) (Arecales: Arecaceae) is the most economically important crop in Oman with an annual production of >360,000 tons of fruit. The Dubas bug (Ommatissus lybicus de Bergevin) (Hemiptera: Tropiduchidae) is one of the major pests of date palms, causing up to a 50% reduction in fruit production. Across the course of 2 seasons, a variety of arthropod predators living in the date palm canopy were investigated for possible biological control of Dubas bugs, given the growing interest in nonchemical insect pest control in integrated pest management. We collected ~6,900 arthropod predators directly from date palm fronds from 60 Omani date palm plantations and tested them for Dubas bug predation using PCR-based molecular gut content analysis. We determined that ≥56 species of arthropod predators feed on the Dubas bug. We found that predatory mites, ants, and the entire predator community combined showed a positive correlation between predation detection frequency and increasing Dubas bug density. Additionally, there was a significant impact of season on gut content positives, with the spring season having a significantly higher percentage of predators testing positive for Dubas bug, suggesting this season could be the most successful time to target conservation biological control programs utilizing a diverse suite of predators.
... There are also unclear effects of predator taxonomic identity at play: studies that tested multiple predator species in identical conditions report differences in half-lives, as well as when and how half-lives are affected by experimental manipulations (Kobayashi et al., 2011;Waldner et al., 2013). Furthermore, even within taxa there is considerable variation in half-lives, with spiders being a notable example of a taxon showing extreme variation (Greenstone et al., 2014); half-life reports for spiders range from two hours (Kerzicnik, Chapman, Harwood, Peairs, & Cushing, 2012) to several weeks (Pompozzi, García, Petráková, & Pekár, 2019). These conflicting and unexplained findings are evidence that half-life experiments thus far have produced few explicit conclusions on how and when organism traits and experimental conditions influence half-lives, highlighting the need for an analysis to explicitly address the factors influencing half-lives. ...
... We fit Equation 1 to the raw data from each paper and took k and h as the slope and half-life, respectively. We used the reported half-lives from two feeding experiments for which raw data were not available (Kerzicnik et al., 2012). ...
Dietary metabarcoding – the process of taxonomic identification of food species from DNA in consumer guts or feces – has been rapidly adopted by ecologists to gain insights into biocontrol, invasive species, and the structure of food webs. However, an outstanding issue with metabarcoding is the semi‐quantitative nature of the data it provides: because metabarcoding is likely to produce false negatives for some prey more often than for other prey, we cannot infer relative frequencies of prey in the diet. To correct for this, we can adjust detected prey frequencies using DNA detectability half‐lives unique to each predator‐prey combination. Because the feeding experiments required to deduce these half‐lives are time‐ and resource‐intensive, our ability to weight the frequency of observations using their detectability has thus far been limited to systems with just a few prey. Here, we present a meta‐analysis of 24 spider prey DNA half‐lives and show that these half‐lives are predictable given predator and prey mass, predator family, digestion temperature, and DNA amplicon length. We further provide a new technique for weighting observations with half‐lives, which allows not just for the ranking of prey in the diet, but reveals the proportion of the diet each prey comprises. Lastly, we apply this method to published dietary metabarcoding data to calculate half‐lives and proportion of the predator’s diet for 35 prey families, demonstrating that this technique can generate improved understanding of diets in real, diverse systems.
... Most Sternorrhyncha prey were aphids (mainly Dysaphis plantaginea (Passerini) and Aphis pomi De Geer). Although aphids are regarded as a low-quality food (Toft, 1995(Toft, , 2005Bilde & Toft, 2001), they appear relatively frequently among the prey of spiders (Alderweireldt, 1994;Harwood, Sunderland & Symondson, 2005;Kerzicnik et al., 2012). ...
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.
... 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.
... When performing molecular gut-content analyses, spiders need to be either small-sized (for total body extraction), split into body parts prior to extraction or be homogenized with a subset used for DNA extraction. Most studies have focused on small-sized spider families such as the Linyphiidae [26,27], small Lycosidae [20,28,29], Theridiidae, Salticidae [30], small Tetragnathidae [31,32] and Oxyopidae [33], in which DNA extraction was made either by homogenizing the whole spider or by crushing the abdomen. Although many studies have used spiders for molecular gut-content analysis, almost none have used medium to large body size spiders (but see Schmidt et al. [2]). ...
Molecular gut-content analysis has revolutionized the study of food webs and feeding interactions, allowing the detection of prey DNA within the gut of many organisms. However, successful prey detection is a challenging procedure in which many factors affect every step, starting from the DNA extraction process. Spiders are liquid feeders with branched gut diverticula extending into their legs and throughout the prosoma, thus digestion takes places in different parts of the body and simple gut dissection is not possible. In this study, we investigated differences in prey detectability in DNA extracts from different parts of the spider´s body: legs, prosoma and opisthosoma, using prey-specific PCR and metabarcoding approaches. We performed feeding trials with the woodlouse hunter spider Dysdera verneaui Simon, 1883 (Dysderidae) to estimate the time at which prey DNA is detectable within the predator after feeding. Although we found that all parts of the spider body are suitable for gut-content analysis when using prey-specific PCR approach, results based on metabarcoding suggested the opisthosoma is optimal for detection of predation in spiders because it contained the highest concentration of prey DNA for longer post feeding periods. Other spiders may show different results compared to D. verneaui, but given similarities in the physiology and digestion in different families, it is reasonable to assume this to be common across species and this approach having broad utility across spiders.
... We used molecular methods to investigate predator-prey interactions. PCR-based techniques are currently widely used to analyse the gut contents of spiders (Greenstone and Shufran, 2003;Kuusk et al., 2008;Sint et al., 2011;Kerzicnik et al., 2012;Chapman et al., 2013;Piñol et al., 2014;Petráková et al., 2015) particularly in cases when the interactions are difficult to observe directly. Similarly to other methods, however, this one has some limits. ...
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.
... The abundance and diversity of canopy-dwelling spiders in orchards throughout the season makes them good candidate biocontrol agents of aphids. The consumption of aphids by spiders has already been demonstrated for a number of spider taxa (e.g., Birkhofer et al., 2008;Kerzicnik et al., 2012;Larsen and Toft, 2008;Toft, 1997Toft, , 1995, including by using molecular gut content analysis (Boreau de Roince et al., 2013;Kuusk and Ekbom, 2012). These studies not only demonstrated that spiders generally prey upon aphids but also that some aphid species are preferred over others (Toft, 1997(Toft, , 1995. ...
... Further, an individual found positive may have preyed upon one or numerous aphids (Harwood and Obrycki, 2005) or may be positive because of scavenging (Von Berg et al., 2012). At the population or community level, differences in the proportion of positive individuals may result from differences in prey availability (Kerzicnik et al., 2012). Here, indeed, we found that the proportion of individuals in which D. plantaginea DNA was detected increased with aphid infestation. ...
Spiders dwelling in the canopy of apple trees may contribute to the control of the rosy apple aphid (Dysaphis plantaginea) in spring. They are expected to be very efficient early in the season during aphid colony establishment. However, their predation on aphids may be impaired by insecticide treatments. In the present study, we aimed to assess the effectiveness of spider predation on D. plantaginea in apple orchards. For this purpose, we sampled a total of 1281 canopy spiders in 8 orchards under IPM (Integrated Pest Management), organic or insecticide-free management in the early and mid-season. DNA analyses of the spider guts with specific D. plantaginea PCR primers were performed to estimate which taxa had eaten this aphid pest in the early and mid-season. Lastly, we assessed the effectiveness of aphid suppression by spiders in insecticide-free orchards during these two periods. The most abundant spiders collected belonged to the Philodromidae, Salticidae and Anyphaenidae families. Spiders were more abundant in the insecticide-free orchards than in the other orchards in the mid-season but not in the early season. The positive detection of D. plantaginea DNA was observed in 8 out of the 12 most abundant families and occurred in all orchards. The probability for a spider to be found positive increased with the abundance of aphids and was higher in the insecticide-free than in the other orchards. It did not depend on the spider prosoma size. Lastly, the increase in the number of aphid colonies early in the season was negatively related to the abundance of Philodromus spp. All these results showed that numerous spider taxa participate in the control of D. plantaginea in organic, conventional and IPM orchards and that Philodromus spp. may be particularly efficient in the early season where arthropod communities are not disturbed by insecticides.
... Analyte D max and its 95% CI were estimated using the original read numbers, the analyte decay rate and the 95% confi-dence envelope of the regression to calculate the time when only one read would be left. A similar method was used to estimate D max from the original data published in McMillan et al. (2007), Kuusk et al. (2008) and Kerzicnik et al. (2012), who studied the detectability of single aphid prey using PCR. In these cases, we calculated the time when only one individual would test positive. ...
... However, analyte D max , determined here from the metagenomic data, was 2-11 times longer than PCR-based D max . We estimated the D max for a single aphid prey using PCR to be 4.0 h for Pardosa sternalis (Aranae: Lycosidae) and 9.8 h for Tetragnatha laboriosa (Aranae: Tetragnathidae) (data from Kerzicnik et al. 2012), 12.9 h for Pardosa spp. (data from Kuusk et al. 2008), and 16.1 h at 14°C and 14.5 h at 21°C for Adalia bipunctata (Coleoptera: Coccinellidae) (data from McMillan et al. 2007). ...
DNA methods are useful to identify ingested prey items from the gut of predators, but reliable detection is hampered by low amounts of degraded DNA. PCR-based methods can retrieve minute amounts of starting material but suffer from amplification biases and cross-reactions with the predator and related species genomes. Here, we use PCR-free direct shotgun sequencing of total DNA isolated from the gut of the harlequin ladybird Harmonia axyridis at five time points after feeding on a single pea aphid Acyrthosiphon pisum. Sequence reads were matched to three reference databases: Insecta mitogenomes of 587 species, including H. axyridis sequenced here; A. pisum nuclear genome scaffolds; and scaffolds and complete genomes of 13 potential bacterial symbionts. Immediately after feeding, multicopy mtDNA of A. pisum was detected in tens of reads, while hundreds of matches to nuclear scaffolds were detected. Aphid nuclear DNA and mtDNA decayed at similar rates (0.281 and 0.11 h−1 respectively), and the detectability periods were 32.7 and 23.1 h. Metagenomic sequencing also revealed thousands of reads of the obligate Buchnera aphidicola and facultative Regiella insecticola aphid symbionts, which showed exponential decay rates significantly faster than aphid DNA (0.694 and 0.80 h−1 respectively). However, the facultative aphid symbionts Hamiltonella defensa, Arsenophonus spp. and Serratia symbiotica showed an unexpected temporary increase in population size by 1-2 orders of magnitude in the predator guts before declining. Metagenomics is a powerful tool that can reveal complex relationships and the dynamics of interactions among predators, prey and their symbionts.This article is protected by copyright. All rights reserved.
... However, these investigations must be only a starting point. We will need DNA gut analysis (Kerzicnik et al., 2012) to provide direct evidence for consumption, and further field studies to quantify the significance of predation. ...
... Given the production risks of dryland farming because of variable weather conditions (Dhuyvetter et al. 1996), wheat is only proÞtable if pest management costs are low or absent. Spiders are proven predators of aphids in wheat (Sunderland et al. 1986, Mansour and Heimbach 1993, Kerzicnik et al. 2012), yet to date, data regarding the spider fauna of eastern Colorado agroecosystems are entirely lacking, as is information on how crop rotations affect spider diversity and abundance. ...
... The early presence of generalist predators in the crop results in more efÞcient biological control of pests (Edwards et al. 1979, Chiverton 1986, Birkhofer et al. 2008. Furthermore, spiders were consistently present in April through June before average peak densities of pests such as D. noxia that typically peak in early to mid-June (Kerzicnik et al. 2012). Spider activity-den-sities were highest from April to July at all sites and declined after this time, likely because of disturbances from wheat harvest. ...
Spiders are critical predators in agroecosystems. Crop management practices can influence predator density and diversity, which, in turn, can influence pest management strategies. Crop intensification is a sustainable agricultural technique that can enhance crop production although optimizing soil moisture. To date, there is no information on how crop intensification affects natural enemy populations, particularly spiders. This study had two objectives: to characterize the abundance and diversity of spiders in eastern Colorado agroecosystems, and to test the hypothesis that spider diversity and density would be higher in wheat (Triticum aestivum L.) in crop-intensified rotations compared with wheat in conventional rotations. We collected spiders through pitfall, vacuum, and lookdown sampling from 2002 to 2007 to test these objectives. Over 11,000 spiders in 19 families from 119 species were captured from all sampling techniques. Interestingly, the hunting spider guild represented 89% of the spider fauna captured from all sites with the families Gnaphosidae and Lycosidae representing 75% of these spiders. Compared with European agroecosystems, these agroecosystems had greater diversity, which can be beneficial for the biological control of pests. Overall, spider densities were low in these semiarid cropping systems, and crop intensification effects on spider densities were not evident at this scale.
