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Interspecific Competition Between Spiders and Its Relevance to Biological Control by General Predators
Abstract
Interspecific competition between two orb-weaving spiders, Metepeira grinnelli (Coolidge) and Cyclosa turbinata (Walckenaer), was investigated by selective removal of the predators. The estimated predation rate of small prey was higher where Cyclosa was alone than where both species were present, because when Metepeira was removed the density of Cyclosa became higher than the combined density of Metepeira and Cyclosa where both species were present and because the consumption rate of small prey by Metepeira was very low compared with that of Cyclosa. The study suggests that, in some circumstances, a subset of predator species could be more effective in reducing prey populations than the entire natural guild.
... Species that benefit from organic farming could be functionally redundant in terms of pest suppression or could negatively affect other pest-consuming predators. Spiller (1986) suggested such a negative effect of greater predator diversity, based upon his finding that a single web-building spider suppressed prey more effectively than in combination with a second web-building spider species. In contrast, Provencher and Riechert (1994) and Riechert and Lawrence (1997) manipulated spider species richness in field-cage experiments and found that herbivore abundance was negatively correlated with increasing predator diversity. ...
... Our results show the complexity of management, predator-prey and intraguild interactions in frequently disturbed agroecosystems. It is necessary to evaluate the extent of such interactions in organically managed agroecosystems as they affect conservation biological control and therefore the sustainability of agricultural management systems (Spiller, 1986;Rosenheim, 1998;Wise 1999, 2001). ...
... This avoidance behavior may be advantageous as it could reduce competition and enhance prey availability for web-owners. This assumption is supported by Spiller (1986) for two web-building spider species, ...
... Perhaps the most definitive approach to identifying the effects of predatorpredator interactions on herbivore population suppression is to conduct studies in which two or more predators, one or both of which is known to prey upon the other, are tested singly and in combination (23,32,36,37,60,91,117,132,150,158,160; see also 145). Such studies show clearly that adding predators to existing predator-prey systems does not consistently enhance the suppression of herbivores. ...
... Spiller (158) demonstrated that the spider Metepeira grinnelli displaced and killed the spider Cyclosa turbinata, resulting in an overall decrease in predation on small arthropod prey compared to predation by C. turbinata alone. Combinations of three predatory mites were generally superior in controlling herbivorous mites than species tested singly, but in some cases the predator Zetzellia mali disrupted mite control by preying on the eggs of another predator, Metaseiulus occidentalis (36, 37). ...
... Interactions between biological control agents need not lead to less effective suppression of herbivores. Many examples exist of natural enemy combinations that produce enhanced control (23, 36, 37, 60,91,145,158,160), and even synergistic interactions are possible (110, 166). The conclusion based on decades of concerted work on the regulation of insect herbivore populations is likely to be appropriate for biological control agents as well: both bottom-up and top-down effects are important. ...
Empirical research has not supported the prediction that populations of terrestrial herbivorous arthropods are regulated solely by their natural enemies. Instead, both natural enemies (top-down effects) and resources (bottom-up effects) may play important regulatory roles. This review evaluates the hypothesis that higher-order predators may constrain the top-down control of herbivore populations. Natural enemies of herbivorous arthropods generally are not top predators within terrestrial food webs. Insect pathogens and entomopathogenic nematodes inhabiting the soil may be attacked by diverse micro- and mesofauna. Predatory and parasitic insects are attacked by their own suite of predators, parasitoids, and pathogens. The view of natural enemy ecology that has emerged from laboratory studies, where natural enemies are often isolated from all elements of the biotic community except for their hosts or prey, may be an unreliable guide to field dynamics.
Experimental work suggests that interactions of biological control agents with their own natural enemies can disrupt the effective control of herbivore populations. Disruption has been observed experimentally in interactions of bacteria with bacteriophages, nematodes with nematophagous fungi, parasitoids with predators, parasitoids with hyperparasitoids, and predators with other predators. Higher-order predators have been little studied; manipulative field experiments will be especially valuable in furthering our understanding of their roles in arthropod communities.
... It has been acknowledged recently that incorporating interactions among predators into ecological theory is crucial for understanding predator-prey and predat or-predator dynamics and their impact on biological control of arthropod pests (Losey and Denno, 1999;Polis et al., 1989;Sih et al., 1998;Soluk, 1993). This is particularly important, because most prey arthropod species are attacked by more than one natural enemy species (Briggs, 1993), and because the use of multiple natural enemy species in biological control of arthropod pests is advocated by some, yet criticized by others (Briggs, 1993;Spiller, 1986). Some authors have argued for screening natural enemies and releasing only the most eVective species (Briggs, 1993;Ehler and Hall, 1982;Turnbull and Chant, 1961;Watt, 1965). ...
... Two predator species may act in a complementary fashion thereby increasing predation risk to the prey (Heinz and Nelson, 1996;Losey and Denno, 1998;Onzo et al., 2004;Riechert and Lawrence, 1997). The two predators may, on the other hand, interfere with each other through intraguild predation or some other forms of interspeciWc interactions, thereby decreasing predation risk to the prey (Rosenheim, 2001;Spiller, 1986). ...
Intraguild predation, one aspect of predator–predator interaction, has received in recent years increasingly greater attention because of mounting evidence of the impact of predator–predator interactions on the structure of ecological communities and biological pest control. In laboratory experiments, we determined if intraguild predation occurs between Typhlodromalus manihoti and Euseius fustis, two phytoseiid mite predators of the cassava green mite Mononychellus tanajoa on cassava in Africa, and if the level of intraguild predation is affected by the availability of the primary prey, M. tanajoa, and maize pollen as alternative non-prey food. In the laboratory, the two predators attacked and killed heterospecific larvae but they did so only when prey mites and alternative food (maize pollen) were absent or scarce. On a diet of intraguild prey alone, the two predator species survived for several days but failed to reproduce. Addition of abundant levels of M. tanajoa and maize pollen increased survival and reproduction of the two predator species and reduced intraguild predation to very low levels. We then determined, on whole plants in pot experiments in a screenhouse, the effect of maize pollen (an alternative food) on the interactions between the two predator species and the impact of predator–predator interactions on suppression of M. tanajoa population densities. In single predator species treatments, both E. fustis and T. manihoti significantly reduced M. tanajoa densities; but surprisingly, E. fustis appeared to be superior to T. manihoti. The co-presence of the two predators on the same cassava plant resulted in similar suppression of M. tanajoa population densities, but greater suppression of M. tanajoa compared with T. manihoti alone, regardless of presence or absence of maize pollen. The presence of the two predator species together reduced their respective abundance compared with single predator species treatments. Addition of maize pollen, however, significantly increased densities of the generalist predator E. fustis, in both single and two predator species treatments; and tilted the balance of the interactions between the two predator species in favour of E. fustis. The findings of our research underscore the role of generalist predators like E. fustis in the suppression of M. tanajoa populations on cassava, and the potential role of alternative non-prey food in altering the interactions between co-occurring predators sharing the same primary prey (by favouring the generalist predators), and the effect of these interactions on suppression of population densities of the shared primary prey.
... For instance, higher numbers of wolf spiders (lycosids) and ground beetles (carabids) did not improve the regulation of insect pest populations, because the predators preyed upon each other rather than preying upon the main insect pests [108]. The orb-weaving spider, Metedeira grinnelli (Coolidge) (Araneidae), was found to displace and prey upon another orb-weaving spider, Cyclosa turbinate (Walckenaer) (Araneidae), resulting in reduced predation on insect pests [109]. Regardless, there is evidence that increasing plant diversity can diminish intraguild predation by generalist predators, subsequently leading to the improved regulation of insect pest populations [97]. ...
Simple Summary
Organic crop production systems typically rely on conservation biological control to increase and sustain natural enemies including parasitoids and predators that will regulate insect pest populations below damaging levels. The use of flowering plants or floral resources to attract and retain natural enemies in organic crop production systems has not been consistent, based on the scientific literature, and most importantly, many studies do not correlate an increase in natural enemies with a reduction in plant damage. This may be associated with the effects of intraguild predation or the negative effects that can occur when multiple natural enemies are present in an ecosystem. Consequently, although incorporating flowering plants into organic crop production systems may increase the natural enemy assemblages, more robust scientific studies are warranted to determine the actual effects of natural enemies in reducing plant damage associated with insect pest populations.
Abstract
Organic crop production systems are designed to enhance or preserve the presence of natural enemies, including parasitoids and predators, by means of conservation biological control, which involves providing environments and habitats that sustain natural enemy assemblages. Conservation biological control can be accomplished by providing flowering plants (floral resources) that will attract and retain natural enemies. Natural enemies, in turn, will regulate existing insect pest populations to levels that minimize plant damage. However, evidence is not consistent, based on the scientific literature, that providing natural enemies with flowering plants will result in an abundance of natural enemies sufficient to regulate insect pest populations below economically damaging levels. The reason that conservation biological control has not been found to sufficiently regulate insect pest populations in organic crop production systems across the scientific literature is associated with complex interactions related to intraguild predation, the emission of plant volatiles, weed diversity, and climate and ecosystem resources across locations where studies have been conducted.
... Predator foraging patterns are also strongly affected by habitat complexity (Uetz 1979, Finke andDenno 2002), with wandering predators being inhibited by complex environments which provide refugia for prey, while ambush predators may find increased hunting success in complex environments due to the availability of concealed areas (Langellotto and Denno 2004). Because of high rates of intraguild predation (Rosenheim et al. 1993, Wise andChen 1999), the use of obligate arthropod predators as biological control agents has shown mixed results with non-tick target taxa (Riechert andLockley 1984, Hodge 1999), but they have been shown to consume large numbers of target prey when applied appropriately (Mansour et al. 1980, Mansour and Whitecomb 1986, Spiller 1986, Snyder and Wise 1999. ...
The primary vector for Lyme disease and several other medically significant tick-borne diseases, Ixodes scapularis (blacklegged tick), spends over 95% of its two-year life cycle exposed to the soil environment. However, the effect of soil-dwelling arthropod predator populations on I. scapularis survival either in the laboratory or under field conditions is unclear. We collected soil-dwelling obligate arthropod predators from the field, representing 13 taxonomic families, and investigated whether they would target two I. scapularis life stages (nymph/engorged larva) under laboratory conditions. After 48 h, 30.6% of the predator species targeted I. scapularis nymphs, while 41.3% targeted engorged larvae. One spider species, Schizocosa ocreata, targeted both I. scapularis life stages reliably under laboratory conditions. We used this species to test whether an arthropod predator would affect I. scapularis survival in field microcosms which contained alternative prey items and a complex soil environment. We also investigated the direct and indirect effects of surface litter on I. scapularis survival by removing the leaf litter layer from half of the microcosms. Predator addition reduced the number of nymphs recovered from the microcosms after 21 d by 32.9%. Litter removal also had a negative effect on tick survival, and interacted weakly with the addition of a predator further decreasing tick survival. Additionally, we found that when leaf litter was removed, I. scapularis survival was positively correlated with the organic matter content of the soil within the microcosms. Naturally occurring arthropod predators may play an important role in regulating population dynamics of I. scapularis and show potential as biological control agents for use in integrated pest management protocols.
... In order to improve biological control of insect pests, the combined use of multiple natural enemy species is a growing trend among biological control programs (Chow et al. 2008). However, multiple predators may interfere with each other by intraguild predation (IGP) (Spiller 1986;Rosenheim 2001;Sohrabi et al. 2013). As a result, IGP has become a central issue in biological control literature. ...
The predatory mites Neoseiulus barkeri
(Hughes) (Acari: Phytoseiidae) and Stratiolaelaps
scimitus Womersley (Acari: Laelapidae) are indige-
nous species used for control of Frankliniella occi-
dentalisPergande(Thysanoptera:Thripidae)inChina.
The present study investigated the interactions
between these two predators and evaluated the effects
of their combined releases to control F. occidentalis in
cucumber andeggplantgreenhousesduringatwo-year
period. Releases of N. barkeri and S. scimitus were
made on the surface of leaves and on soil adjacent to
plant roots at a density of 100 per plant, respectively.
Although releases of either N. barkeri or S. scimitus
alone significantly reduced both adult and larval F.
occidentalisdensities,combinedreleasesofN.barkeri
and S. scimitus greatly improved F. occidentalis
control. However, some negative interactions between
the two predators did occur. The mean levels of adult
and larval F. occidentalis suppression on cucumber
plants were 62 and 51 %, and the mean levels of adult
and larval F. occidentalis suppression on eggplant
plants were 66 and 66 %. Results also revealed that N.
barkeri and S. scimitus successfully established pop-
ulations in the target microhabitats. Moreover, preda-
tors established populations more easily on cucumber
compared to eggplant crops. These results highlight
the potential use of N. barkeri in combination with S.
scimitus for control of F. occidentalis.
... As sedentary generalist predators, web-building spiders have long been suggested to have resource-based niche separation, with interspecific competition playing a role in web placement and diet differences among similar species (Wise 1995). Early studies suggested that niche separation is mediated mainly by interspecific interference competition over high quality web sites (Spiller 1984, Spiller 1986, Toft 1987. Wise (1995) strongly criticized the interpretation of the results of these studies, and upon re-analysis of data he concluded that there was little, if any, support for the occurrence of interspecific competition in spiders. ...
Competition for resources is a major organizing principle in communities of organisms that share similar ecological niches. Niche separation by means of exploitation or interference competition was investigated in two taxa of crop-inhabiting spiders that overlap in microhabitat use and have similar web design. Competition for prey and web sites was tested in microcosm experiments with the most common species that build sheet-webs: Enoplognatha gemina (Theridiidae) and Alioranus pastoralis (Linyphiidae). A field survey over the crop season provided data on spatial and temporal dispersion of Enoplognatha spp. (Theridiidae) and linyphiid spiders (Linyphiidae) and on availability of prey over the season. In the microcosm experiments, both taxa took springtails as prey, but only Enoplognatha fed on aphids. Differences in diet, however, could not be attributed to either exploitative or interference competition. Spatial separation of websites was attained by vertical displacement of webs in the vegetation (Enoplognatha) and by avoidance of patches occupied by conspecific or heterospecific individuals (linyphiids). In the field, densities of linyphiids and Enoplognatha were correlated negatively and webs were over-dispersed relative to a random distribution. Both taxa colonized the field at the start of the season; linyphiids colonized as adults, quickly reproduced, and had a second adult peak; Enoplognatha matured in the middle of the season and their numbers remained fairly constant over the season. The combined experimental manipulations and field data suggest that niche separation occurs at different scales. The hypothesis of competition for websites was partially supported, while prey preference (or tolerance) and temporal differences in life history stages also may explain the negative correlations between densities of the two taxa.
... However, as Breene et al. (1993) note, the ability to engage in cannibalism and intraguild predation during times of low pest abundances may help maintain spider populations at some minimum in the crop fields. Spiller (1986) found that competition limited the predatory efficiency of the two species salt marsh system he worked on. He proposed that Cyclosa alone would better limit herbivore numbers than a combination of Metepeira and Cyclosa because the interference interactions between the two would limit Cyclosa densities. ...
Spider competition has long been an elusive phenomenon for ecological study. Because most spiders are generalist predators, they are predicted to overlap in resource use wherever they overlap in space use and activity periods. However, despite this obvious potential for competition, the empirical evidence for competition has been weak. Spider competition could potentially limit densities in agricultural ecosystems, which would limit their effectiveness as biological control agents. We summarize the results of five studies in a type of ecosystem which may be considered to be analogous to row crops in both the physiognomy of vegetation and cyclic disturbance regimes, namely, wetlands. In addition, we summarize the results of our own work in a soybean ecosystem.
... Within a guild of generalist predators, then inter-speciÞc predation, cannibalism, and interspeciÞc and intraspeciÞc competition for prey all may occur (Spiller 1984(Spiller , 1986Hurd 1988;Polis et al. 1989;Anholt 1990;Wise and Wagner 1992). According to traditional guild theory, we ought to be able to Þnd ways in which this common prey resource pool divided up to minimize or avoid competition. ...
We examined changes of site selection by the mantid Tenodera aridifolia (Stoll) according to its developmental stage. We investigated the vegetation characteristics selected by mantids of different developmental stages at three field sites. The height of vegetation and height at which mantids were found on vegetation tended to be higher for later-instar mantids than early instars. Mantids tended to prefer the upper part of vegetation regardless of their developmental stage or the site. Later-instar mantids also tended to select larger-sized leaves for perching compared with early instar mantids. Height above ground, vegetation height, and leaf sizes selected by mantids differed among the three sites. In addition, the preferred plant species used by mantids also changed with their developmental stage. Thus, our results indicate that T. aridifolia has varying preferences for site selection and specific vegetation according to its developmental stage.
... The dynamics of generalist predators in terrestrial communities involve a multitude of interactions and processes complicating clear-cut predictions of community effects. Intraguild interactions such as predation (Polis et al. 1989), exploitation competition (Lenski 1982, Spiller 1986 or cannibalism (Fox 1975) produce confounding indirect community effects (Sih et al. 1985, Wootton 1994. Experiments show that generalist arthropod predators may play an important role in shaping community structure (Fagan and Hurd 1994) and that they can produce cascade effects down to plant level Bishop 1990, Moran et al. 1996). ...
I examine feeding rate and reproduction of a generalist arthropod predator Pterostichus cupreus (Coleoptera, Carabidae) at two different densities in two agricultural habitats where this beetle is commonly found; perennial ley and annual barley. I also examine effects of predator densities on arthropod community composition in each crop. The aims are to, in each of these habitats, examine if 1) previously observed food limitation in nature is caused by competition for food where prey is depleted by the competitors, or because predators starve because it is inherently difficult for them to find or consume food in a poor habitat where prey abundance is insensitive to the level of predation, and 2) to examine impact, directly or indirectly, of the predator on arthropod community composition. Predator density was manipulated in plots surrounded by barriers (Treatment) in the two habitats (Crop), and the experiment was repeated early and late in the growing season (Time). Large differences in community composition were found between crops and times. Arthropod abundance was always higher in ley, and increased markedly between the first and second experiment in barley. Predator load was high (44%) in barley in the first experiment compared to the second (26%) and compared to ley (22%). Eggload, amount of stored fat and live body weight of P. cupreus were all markedly higher in ley. The lower fat content in recaptured beetles in barley indicated lower feeding rates and a high degree of food limitation compared to ley. Indications that fat storage was reduced by intraspecific competition were found, but the main difference in fat storage was between crops. No significant treatment effects of initial predator density were detected on arthropod community composition in each crop. Food limitation was mainly caused by difficulty to find food in the barley. Adult feeding and reproduction indicates that barley and ley represent widely different habitat qualities to P. cupreus. The composition and spatial arrangement of perennial and annual crops in the agricultural landscape may be important to long-term predator population dynamics.
... Among the number of factors on which the interactions within guilds are assessed, body size (biomass) of constituent predators is a crucial one that influences success or failure in the guild (Lucas et al. 1998;Felix and Soares 2004;Armsby and Tisch 2006;Mochizuki et al. 2006). Larger species have a competitive advantage over smaller species during interference competition, where owing to their large size and higher consumption rates (Finlayson et al. 2010), they physically interfere with their competitors and/or prey upon them (Lawton and Hassell 1981;Persson 1985;Spiller 1986;Wissinger and McGrady 1993;Sato et al. 2008). In prey abundant conditions of aphidophagous guilds, larger ladybirds are more effective than the smaller ladybirds but not so under prey scarce conditions (Sloggett 2008). ...
Multiple interactions occurring within aphidophagous guilds determine their final predation outcomes, i.e., antagonistic, additive, or synergistic. Based on these predatory outcomes, the suitability of guilds in suppressing aphid pests is determined. The present study assesses the efficacy of 11 guilds, formed from both larval and adult stages of four locally abundant aphidophagous coccinellids (Coleoptera: Coccinellidae), while exploiting the pea aphid, Acyrthosiphon pisum Harris (Hemiptera: Aphididae). The observed antagonistic effects within these guilds are resultants of enhanced predator–predator interactions due to the size and diversity of guild predators. Smaller ladybird predators maintained their usual body mass, probably by increasing their conversion efficiencies to compensate for their reduced prey consumption. However, larger ladybirds reported loss in their body mass, owing to their higher energy needs. The overall guild conversion efficiencies and growth rates were reduced. Among the experimental guilds, the observed prey mortalities were relatively higher in two-predator guilds, and within these two-predator combinations, the higher prey mortalities were recorded in those guilds where Coccinella septempunctata was one of the predators.
... In some cases, due to the absence of inter-guild feeding activity and other interferences, applying a single predator species against a pest can be more effective when compared with the use of multispecies (Spiller, 1986). Other studies, however, have documented that assemblage of many spider species is more effective at reducing prey densities than a single species of spider (Greenstone, 1999;Sunderland, 1999). ...
Abstract.The tea (Camellia sinensis(L.) Kuntze) industry is the backbone of the
agroeconomy of the North Bengal region located at the foothills of the Himalayas in
North-East (NE) India. This region accounts for about 25% of the total tea production
in India. The tea mosquito bug, Helopeltis theivoraWaterhouse, is one of the most
devastating sucking pests of tea in this region. Various kinds of synthetic insecticides are
continuously sprayed to control this bug. The lynx spiderOxyopes javanusThorell has been
found to remain associated with tea plants and feed on H. theivora. The present study
investigated the predation potential and efficacy of theO. javanusspider against one of its
most common prey species,H. theivora. In the laboratory, with an increase in H. theivora
density, the predation rate of both male and femaleO. javanusincreased. Per capita
predation rates exhibited by male and femaleO. javanusper day against adultH. theivora
were 3.67^1.52 and 11.67^1.53 (mean^standard deviation), respectively. At a
reasonably small prey density, the prey consumption rate was highest, reaching up to
100%, indicating that the spider predator has the potential to eliminate smaller
populations of the pest. The predation effectiveness calculated using Holling’s disc
equation was 6.08 and 356.58 for male and femaleO. javanus, respectively. The prey
handling time was 0.138 day for maleO. javanusand 0.012 day for femaleO. javanus.
FemaleO. javanusexhibited about fivefold higher searching efficacy than maleO. javanus.
It appears that the conservation or augmentation of O. javanusin the tea ecosystem
can provide effective biological management of the major tea pest, H. theivora,in
sub-Himalayan foothills and plains of NE India.
... Losey and Denno (1998), for example, reported that a combined release of a foliar-and a ground-foraging predators resulted in predator facilitation which means that more prey than expected were consumed. Combined release of predators may also result in less prey consumed than expected (Spiller, 1986;Rosenheim et. al. 1993). ...
Interactions among predators may have a substantial impact on the total efficiency of a predator complex. The effect of intra-and interspecific interactions of the generalist predators Orthotylus marginalis (Heteroptera: Miridae) and Anthocoris nemorum (Heteroptera: Anthocoridae) was investigated in a laboratory experiment on potted plants of Salix viminalis. The effect of intra-and interspecific interactions was measured as predation rates on eggs and larvae of the blue willow beetle Phratora vulgatissima (Coleoptera: Chrysomelidae). The direction of the interaction effects was determined by comparing predation rates of single individuals with those of two individuals of the same or different species. (1) There was a non-additive, antagonistic effect on predation rates due to intraspecific interactions between individuals of A. nemorum, whereas intraspecific interactions did not affect predation rates in O. marginalis. (2) Interspecific interactions between A. nemorum and O. marginalis did not affect total predation rates. The combined effect of the two predators on willow beetle mortality was not different from the sum of the single individual species impact.
... The varied effects of using multiple predator speciess are reflected in the opinion of ecologists and biocontrol researchers; some favour thee use of one natural enemy species (cg. y Myers, 1985;Spiller, 1986;Rosenheim et a/., 1993),, but others favor the use of multiple natural enemv species as long as thev act in a complementaryy fashion (r,^., Heinz and Nelson, 1996;Riechert and Lawrence, 1997;Losey andd Denno, 1998). ...
... With respect to long-term biological control, the question of using single versus multiple natural enemy species, therefore, remains controversial (Kakehashi et al ., 1984;Briggs, 1993;McEvoy & Coombs, 1999). The varied effects of using multiple predator species are reflected in the opinion of ecologists and biocontrol researchers; some favour the use of one natural enemy species (e.g., Myers, 1985;Spiller, 1986;Rosenheim et al ., 1993), but others favor the use of multiple natural enemy species as long as they act in a complementary fashion (e.g., Heinz & Nelson, 1996;Riechert & Lawrence, 1997;Losey & Denno, 1998). ...
The issue of introducing single or multiple natural enemy species for classical biological control has been an area of intense inquiry by ecologists and biological control practitioners. This is particularly relevant to classical biological control of cassava green mite Mononychellus tanajoa (Bondar) (Tetranychidae) in Africa, as this pest mite is shared by several natural enemies in the Neotropics (its area of origin), two of which have been introduced and established widely in Africa. We conducted two screenhouse experiments using the two neotropical phytoseiid predatory mites, Typhlodromalus aripo DeLeon and Typhlodromalus manihoti Moraes, to determine the effects of single and two-predator species on population dynamics of the two predators and on suppression of M. tanajoa populations. The two predators are thought to be complementary in their impact on their shared prey M. tanajoa, due to similarities in their preference for this prey and to differences in their spatial distribution and foraging activities on cassava. The two predator species were released alone or together at low and at high initial densities of M. tanajoa. In all cases, predator releases resulted in significant suppression of M. tanajoa, but the degree of suppression did not differ among single and two-species releases with one exception: at high initial density of M. tanajoa, releases of T. aripo alone had less impact than that of either T. manihoti alone or of the two species together. Typhlodromalus aripo also appeared to be inferior as a competitor of T. manihoti: at low initial density of M. tanajoa, the proportion of T. aripo in the two-predator release treatments gradually declined and was strikingly lower than in the single species release, probably due to intraguild predation on its larvae by T. manihoti. However, T. aripo persisted longer than T. manihoti after elimination of M. tanajoa. On the basis of this study under semi-natural conditions, it appears that either species is sufficient for controlling M. tanajoa populations, with T. manihoti being more efficient at high initial prey densities and T. aripo at low initial prey densities. At high prey density, T. manihoti increased to large numbers and outcompeted T. aripo. Relevance of these findings to larger spatial scale and under natural conditions is discussed.
... Henaut et al. (2001) reported prey partitioning among araneids. However, Spiller (1986), Wise (1983), and Schaefer (1978) reported evidence that interspecific competition may some time be a significant factor in a spider community. ...
The present study was conducted to investigate possible
factors responsible for the coexistence of 3 hunting spiders (Lycosa terrestris, Pardosa birmanica, and Oxyopes
javanus) and 2 orb web spiders (Tetragnatha javana and Neoscona theisi) in a rice ecosystem of central
Punjab, Pakistan. For this purpose 2 plots (each of 400 m2) were selected in a monoculture area of Sheikupura
District, Punjab, Pakistan. The active density of spiders during the study period was recorded by pitfall trap
and a suction device. Data showed that the active density of all spider species significantly differed among
different trapping sessions. Members of both guilds fed on the same prey orders but in different proportions.
Their reproductive period, abundances of young and adults, and prey size also differed. A positive correlation
was found between the carapace width of a spider and prey it took. Values of resource overlap indicated
that species of a guild were utilizing time, habitat, prey size, and prey taxa differently. A discriminant function
analysis also clearly separated the 5 species in the 3 dimensional space. It was concluded that separation of
guild members in time, microhabitat, and prey niche dimensions reduced competition, thus allowing coexistence.
http://zoolstud.sinica.edu.tw/Journals/49.4/470.pdf
... Interactions among natural enemy species can have two opposite effects on target pest population (Losey and Denno 1999; Wekesa et al. 2007). Two predator species may act in a complementary fashion, thereby increasing predation risk to the prey (Heinz and Nelson 1996; Losey and Denno 1998; Onzo et al. 2004 Onzo et al. , 2005 Riechert and Lawrence 1997); or two predators may interfere with each other through intra-guild predation or some other forms of interspecific interactions, and their less-than-additive effects would reduce predation risk to the prey (Rosenheim 2001; Spiller 1986). Interactions between natural enemies are particularly relevant to classical biological control of the cassava green mite (CGM), Mononychellus tanajoa (Bondar) (Acari: Tetranychidae), in Africa, because this pest is attacked by several natural enemies. ...
The predatory mite Typhlodromalus aripo and the entomopathogenic fungus Neozygites tanajoae, both introduced from Brazil for control of the cassava green mite (CGM) Mononychellus tanajoa, now co-occur in cassava fields in Benin. However, studies on interactions between these two natural enemies and how they might affect CGM biological control are lacking. We determined in screenhouse experiments the effects of single and combined releases of N. tanajoae and T. aripo on CGM suppression. In the single natural enemy treatment, both T. aripo and N. tanajoae significantly reduced CGM densities, but the results of the predator (T. aripo) are more quickly measurable than those of the pathogen (N. tanajoae) in our short-term experiment. The level of CGM suppression in the combined natural enemy treatment was reduced considerably compared with T. aripo-alone, but only slightly when compared with N. tanajoae alone, with a simultaneous reduction in T. aripo and N. tanajoae abundance or prevalence. In a laboratory experiment, T. aripo fed more on N. tanajoae-infected CGM than on healthy CGM and its oviposition and survival were reduced when fed on the former compared with the latter, which can help in explaining the reduction in numbers of T. aripo and consequently the considerable loss in suppression of CGM in the combined natural enemy treatment in the screenhouse experiment. Together, the screenhouse and the laboratory experiments predicted negative interactions between the two natural enemies with negative consequences for CGM biological control. Long-term field observations and rigorous field experiments that simultaneously manipulate T. aripo and N. tanajoae abundance and prevalence are needed to validate the prediction of this study.
... Ongoing efforts involve establishing a complex of predators. Such an effort requires knowledge of interspeciÞc or intraguild competition among predators (Spiller 1986, Heinz and Nelson 1996, Losey and Denno 1998, Rosenheim 2001, Onzo et al. 2004). Flowers et al. (2005Flowers et al. ( , 2006) measured the interaction among three heterospeciÞc predator species of A. tsugae and found no negative competitive interactions among the species. ...
Predation, egg production, and survivorship of Laricobius nigrinus Fender, L. rubidus LeConte, and L. osakensis Montgomery and Shiyaki, predators of hemlock woolly adelgid, Adelges tsugae Annand, were investigated in the laboratory and in the field. In individual assays in the laboratory, L. rubidus oviposited fewer eggs than either L. nigrinus or L. osakensis. In assays containing congeneric or conspecific groups of adult Laricobius, L. osakensis preyed upon the greatest number of ovisacs. The number of ovisacs preyed upon was not different between treatments with all three species and those with only L. osakensis or L. nigrinus. Adult predators fed on few predator eggs and when they did no species preference was observed. The numbers of A. tsugae ovisacs fed upon did not differ significantly by groups of congeneric or conspecific Laricobius larvae. Laricobius adults and larvae had high survival rates throughout all experiments. In the field, L. nigrinus and L. rubidus were enclosed in sleeve cages with both high (>120 ovisacs) and low (<90 ovisacs) A. tsugae densities for 1 wk. All branches with caged beetles had significantly greater numbers of ovisacs preyed upon than branches caged without beetles. No differences in predation or egg production were found among the conspecific and congeneric groupings. Predation was uniformly greater on high prey-density branches than on low prey-density branches. Survivorship among predators did not differ significantly at either prey density. Results from both laboratory and field experiments suggest that these species are able to coexist and can be released in the same location for biological control of A. tsugae.
... Multiple predators often affect prey in ways that cannot be predicted simply by adding the independent linear effects of single predator types. Indeed, either more or fewer prey may be consumed in the combined release of predators compared with adding two single predators individually (Spiller, 1986;Rosenheim et al., 1993;Losey & Denno, 1998;Sih et al., 1998). However, a negative interaction between predators may not necessarily hinder a depression of the prey population (Lang, 2003). ...
1. Interactions among predators may influence the total efficiency of a predator complex. The effect of intra- and interspecific interactions of the generalist predators Orthotylus marginalis (Heteroptera: Miridae) and Anthocoris nemorum (Heteroptera: Anthocoridae) was investigated in a laboratory experiment. Outcomes of the interactions were determined by comparing predation rates on eggs and larvae of the blue willow beetle Phratora vulgatissima of single individuals with those of two individuals of the same or different species.
2. A non-additive, antagonistic effect on predation rates due to intraspecific interactions was found between individuals of A. nemorum. No such effect was found in O. marginalis. These results are as expected as a consequence of differences in behaviour of the two predator species: A. nemorum is a much more active and mobile predator than O. marginalis.
3. Contrary to expectation, interspecific interactions between A. nemorum and O. marginalis did not affect the total predation rate.
4. An observation from the field corroborated the results obtained in the laboratory study; there was no negative relationship between the densities of the two predator species, indicating that the two species do not interact negatively in the field at their natural densities.
5. It is concluded that the additive effect of multiple predator species is of potential value in biological control.
... The second reason to think that intraguild predation might be a problem for biological control came from some of the earliest experimental studies of multipredator biological control systems, which demonstrated exactly this unwanted outcome (Hoy et al. 1972, Press et al. 1974, Spiller 1986. Some of these studies were discussed by Polis and Holt in their early reviews. ...
The experimental literature on the effects of intraguild predation on population growth rates of herbivorous arthropod prey
has expanded substantially in the last decade, creating a body of results that can be used to test hypotheses relevant to
biological control. Here we present a formal meta-analysis of the published experimental literature to assess two hypotheses:
(1) intraguild predation causes an increase in the density of the shared herbivore prey, and (2) ‘coincidental intraguild
predation’, in which a predatory arthropod (the ‘intraguild predator’) consumes a herbivore that harbors a developing parasitoid
(the ‘intermediate predator’), is less likely to disrupt biological control than is ‘omnivorous intraguild predation’, in
which the intermediate predator is consumed directly. The meta-analysis reveals that intraguild predation does not universally
cause an increase in the density of the shared prey; instead, the mean effect size viewed across all studies is not significantly
different from zero, and there is strong variability in effects across studies. The meta-analysis also reveals a marginally
significant difference between the effects of coincidental and omnivorous intraguild predation: inclusion of a coincidental
intraguild predator significantly enhances biological control, at least in the short-term trials included in our database,
whereas inclusion of an omnivorous intraguild predator has little overall effect. Thus, our analysis highlights the diversity
of effects generated by intraguild predators within arthropod communities. The discrepancy between theory and empirics appears
likely to stem from their different time-frames, with theory often emphasizing equilibria and experimentation examining instead
short-term transients, and also with the artificial simplification of arthropod communities depicted in theoretical treatments.
More work, both theoretical and empirical, is needed to bridge the gap between theory and observation and to develop a deeper
understanding of factors generating the observed diversity of intraguild predator effects.
... Spiders are important natural enemies of many insect pests, as they are generalist predators and comprise a large part of the beneficial arthropod community in agricultural fields (Nyffeler, 1982;Sunderland etaI., 1986;Young & Lockley, 1985). Recent reviews (Riechert & Lockley, 1984;Nyffeler & Benz, 1987;Everts, 1990), experiments (Spiller, 1986) and a number of case studies in different crops (e.g. Kiritani et al., 1972;Luczak, 1980;Mansour et al., 1981;Dean et al., 1987;Nyffeler & Benz, 1988) show that spiders can indeed be effective pest control agents in many situations. ...
Pesticides may affect the predatory and reproductive behaviour of beneficial arthropods short of having direct effects on their survival. We present a bioassay designed to test (ultimately in the field) such hidden effects of agrochemicals in their application concentrations. As a paradigm we chose the web-building behaviour of the cross spider Araneus diadematus Clerck (Araneidea, Argiopidae) and we selected four commonly used pesticides: Oleo Rustica 11E (mild insecticide), Fastac (pyrethroid insecticide), Bayfidan and Sportak (fungicides). Neither fungicides nor the mild insecticide seem to affect web-building behaviour significantly, whereas the pyrethroid insecticide suppressed web-building frequency and severely affected web size and building accuracy.
... The net outcome from several natural enemies may be either additive, the sum of parts, (Samways, 1986) or synergistic, greater than the sum of parts (Losey and Denno, 1998). However, negative interactions between natural enemies could result in antagonistic (less than the sum of parts) effects (Spiller, 1986;Ewans, 1991;Ferguson and Stiling, 1996). One concept is that species with very similar behaviors and feeding habits would be more likely to interact antagonistically, whereas the chances of finding additive or even synergistic interactions between species would increase with increasing differences in behaviour (Sih et al., 1998). ...
The natural enemies attacking eggs (and young larvae) of the willow leaf beetle Phratora vulgatissima were identified in the field. Three heteropterans were common natural enemies. The mirid Orthotylus marginalis was the most abundant and had an intermediate consumption rate in the lab, whereas the mirid Closterotomus fulvomaculatus was the least abundant but had the highest consumption rate. The anthocorid Anthocoris nemorum was intermediate in abundance but had the lowest consumption rate. However, the experimental situation (in petridish or on shoot) affected the ranking of the predators and illustrates behavioral differences. The anthocorid was very mobile and could be characterized as a run and eat predator, whereas the mirids were less mobile and behaved to a find and stay principle. Possible consequences of interspecific variation in behavior, from a biological control perspective, are discussed.
... First, two predators may induce complementary effects thus increasing the risk posed to the prey (Heinz and Nelson 1996;Riechert and Lawrence 1997;Loosey and Denno 1998;Onzo et al. 2004Onzo et al. , 2005). Second, the two predators may interfere with each other such that the predation risk to the shared prey is decreased (Spiller 1986;Finke and Denno 2003;Cakmak et al. 2006;Abad-Moyano et al. 2010). Third and largely theoretical, the interactions of both species could have no effect on the prey. ...
Neoseiulus neobaraki and N. paspalivorus are amongst the most common phytoseiid predators of coconut mite, Aceria guerreronis, found in the spatial niche beneath coconut fruit bracts. Both predators may occur on the same coconut palms in Benin and Tanzania and are therefore likely to interact with each other. Here, we assessed cannibalism and intraguild predation (IGP) of the two predators in the absence and presence of their primary prey A. guerreronis. In the absence of the shared extraguild prey, A. guerreronis, N. neobaraki killed 19 larvae of N. paspalivorus per day and produced 0.36 eggs/female/day, while the latter species killed only 7 larvae of the former and produced 0.35 eggs/female/day. Presence of A. guerreronis only slightly decreased IGP by N. neobaraki but strongly decreased IGP by N. paspalivorus, which consumed 4-7 times less IG prey than N. neobaraki. Resulting predator offspring to IG prey ratios were, however, 4-5 times higher in N. paspalivorus than N. neobaraki. Overall, provision of A. guerreronis increased oviposition in both species. In the cannibalism tests, in the absence of A. guerreronis, N. neobaraki and N. paspalivorus consumed 1.8 and 1.2 conspecific larvae and produced almost no eggs. In the presence of abundant herbivorous prey, cannibalism dramatically decreased but oviposition increased in both N. neobaraki and N. paspalivorus. In summary, we conclude that (1) N. neobaraki is a much stronger intraguild predator than N. paspalivorus, (2) cannibalism is very limited in both species, and (3) both IGP and cannibalism are reduced in the presence of the common herbivorous prey with the exception of IGP by N. neobaraki, which remained at high levels despite presence of herbivorous prey. We discuss the implications of cannibalism and IGP on the population dynamics of A. guerreronis and the predators in view of their geographic and within-palm distribution patterns.
... In pest management, the use of multiple natural enemies versus the use of a single species has been a long-debated controversial issue (Hassell, 1978;Ehler, 1990;DeBach and Rosen, 1991;Waage and Mills, 1992;Sunderland et al., 1997;Bellows and Hassell, 1999). Compared to the effect of a single species, multiple natural enemies have been documented to enhance pest suppression (Heinz and Nelson, 1996;Riechert and Lawrence, 1997;Losey and Denno, 1998), to reduce effectiveness in pest control (Spiller, 1986;Rosenheim et al., 1993;Ferguson and Stiling, 1996), or to suppress the target pest in a way that reflects the sum of the individual species effects (Chang, 1996). ...
Interactions such as competition, intraguild predation (IGP), and cannibalism affect the development and coexistence of predator populations and can have significance for biological control of commonly exploited pest organisms. We studied the consequences of combined versus single release of two predaceous mite species (Phytoseiidae), with differing degrees of diet specialization, on their population dynamics and the suppression of the carmine spider mite, Tetranychus cinnabarinus Boisduval (Tetranychidae), on greenhouse-grown gerbera. Population growth of the specialist predator Phytoseiulus persimilis Athias-Henriot was greater and population decline steeper when released in combination with the generalist Neoseiulus californicus McGregor than when released alone. In contrast, the N. californicus population grew and declined more gradually when released in combination with P. persimilis, compared to the single species release. The differential impact on each other's population dynamics can be primarily attributed to contrasting properties in competition, IGP, and cannibalism. At the same overall predator density and as long as prey was abundant, the specialist P. persimilis was more strongly affected by intraspecific competition than by interspecific competition with the generalist N. californicus. In contrast, interspecific competition with P. persimilis had a greater impact on N. californicus than intraspecific competition. After prey depletion, the generalist predator N. californicus was more likely to engage in IGP than was the specialist predator P. persimilis. Overall, the study demonstrates that prey specificity has significance for the quality and intensity of predator–predator interactions and indicates potential implications for biological control of spider mites. All predator releases (i.e., either species alone and both species in combination) resulted in reduction of the spider mite population to zero density. Individual release of the specialist P. persimilis led to the most rapid spider mite suppression. Nonetheless, in perennial greenhouse-grown crops P. persimilis and N. californicus could have complementary effects and a combination of the two predators could enhance long-term biological control of spider mites. The potential risks and benefits associated with the release of both species are discussed.
... Although this experiment was not designed to assess the relative efficacy of different biocontrol agents, it does demonstrate how careful researchers must be when selecting biocontrol agents. As has been reported for interspecific interactions within multispecies assemblages of biological control agents (e.g., Spiller, 1986;Ehler, 1992; but see Chang, 1996), interactions between chemical and biological control agents may be detrimental to pest control efforts. ...
Integrated pest management attempts to combine cultural, chemical, and biological approaches to bring about pest reductions and improve crop yields. In Asian wet rice agriculture, as in many crop systems, there is a real question as to how compatible chemical control methods are with other pest control approaches. Working in an irrigated rice paddy on Java, Indonesia, we crossed a natural enemy treatment (addition of wolf spiders,Lycosa pseudoannulataBoesenberg et Strand) with an insecticide treatment (monocrotophos) in a balanced, replicated, two-way factorial design to explicitly examine the potential interactions between chemical and biological control methods. Although adding either wolf spiders or insecticide to field plots significantly reduced abundance of pests (sucking homopterans), combining the two treatments together generated a significant, season-long interaction effect such that pest densities did not decrease. In other words, pest densities in plots receiving both spiders and insecticide were statistically comparable to those in plots receiving neither pest control method. Furthermore, we found additive effects of wolf spiders and insecticide on other generalist predators, and from those data we hypothesize that intraguild predation and ensuing indirect effects may be responsible for the interaction effect on pest density. Our results indicate that, far from being complementary and compatible approaches to pest reduction, combining treatments of natural enemy addition and insecticide application may be quite counterproductive.
... Interactions among natural enemy species can have two opposite effects on target pest population (Losey and Denno 1999;Wekesa et al. 2007). Two predator species may act in a complementary fashion, thereby increasing predation risk to the prey (Heinz and Nelson 1996;Losey and Denno 1998;Onzo et al. 2004Onzo et al. , 2005Riechert and Lawrence 1997); or two predators may interfere with each other through intra-guild predation or some other forms of interspecific interactions, and their less-than-additive effects would reduce predation risk to the prey (Rosenheim 2001;Spiller 1986). ...
... Recent empirically based models of the structure and function of terrestrial communities have suggested that different predator taxa may play different ecological roles: some predators ("intermediate predators") may operate primarily from the third trophic level, suppressing herbi-vore populations, whereas other predators ("top predators") may operate primarily from the fourth trophic level, suppressing populations of intermediate predators and thereby releasing herbivore populations from control (Hurd and Eisenberg 1990;Polis 1991Polis , 1994Polis , 1999Wise 1993;Polis and Strong 1996;Janssen et al. 1998;Rosenheim 1998;Halaj and Wise 2001). In nature, many predators have been shown experimentally to act as intraguild predators, straddling the third and fourth trophic levels by feeding both on herbivore prey and on other predators with whom they compete for access to those prey, and producing highly variable effects on herbivore population growth rates (Spiller 1986;Rosenheim et al. 1993Rosenheim et al. , 1999Rosenheim 2001;Snyder and Ives 2001;Snyder and Wise 2001;Denno 2002, 2003;Lang 2003;Chang and Eigenbrode 2004). These models and experiments have focused attention on a new and fundamental question: what traits predispose a predator to feed predominantly on herbivores versus on other predators? ...
Recent work in terrestrial communities has highlighted a new question: what makes a predator act as a consumer of herbivores versus acting as a consumer of other predators? Here we test three predictions from a model (Rosenheim and Corbett in Ecology 84:2538-2548) that links predator foraging behavior with predator ecology: (1) widely foraging predators have the potential to suppress populations of sedentary herbivores; (2) sit and wait predators are unlikely to suppress populations of sedentary herbivores; and (3) sit and wait predators may act as top predators, suppressing populations of widely foraging intermediate predators and thereby releasing sedentary herbivore populations from control. Manipulative field experiments conducted with the arthropod community found on papaya, Carica papaya, provided support for the first two predictions: (1) the widely foraging predatory mite Phytoseiulus macropilis strongly suppressed populations of a sedentary herbivore, the spider mite Tetranychus cinnabarinus, whereas (2) the tangle-web spider Nesticodes rufipes, a classic sit and wait predator, failed to suppress Tetranychus population growth rates. However, our experiments provided no support for the third hypothesis; the sit and wait predator Nesticodes did not disrupt the suppression of Tetranychus populations by Phytoseiulus. This contrasts with an earlier study that demonstrated that Nesticodes can disrupt control of Tetranychus generated by another widely foraging predator, Stethorus siphonulus. Behavioral observations suggested a simple explanation for the differing sensitivity of Phytoseiulus and Stethorus to Nesticodes predation. Phytoseiulus is a much smaller predator than Stethorus, has a lower rate of prey consumption, and thus has a much smaller requirement to forage across the leaf surface for prey, thereby reducing its probability of encountering Nesticodes webs. Small body size may be a general means by which widely foraging intermediate predators can ameliorate their risk of predation by sit and wait top predators. This effect may partially or fully offset the general expectation from size-structured trophic interactions that smaller predators are subject to more intense intraguild predation.
... Single-species studies are necessary to evaluate the effects of artiÞcially increasing spider densities in relatively isolated systems that have been denuded of their original fauna, such as greenhouses and highly altered agroecosystems. Some evidence suggests that single spider species can be more effective than an assemblage in reducing pests, because spiders also prey upon one another (Spiller 1986). Other studies have shown that assemblages are more effective (Riechert and Lawrence 1997). ...
Spiders, particularly assemblages of species, have been shown to be effective in reducing pest insects and crop damage in field crops and orchards. We investigated the potential for a single jumping spider species to reduce pests in a greenhouse setting. We placed three treatments in large enclosures: 1) control treatment of only sweet basil, Ocimum basilicum L.; 2) sweet basil and a phytophagous pest, fourlined plant bug, Poecilocapsus lineatus (F.) (Heteroptera: Miridae); and 3) sweet basil, fourlined plant bug, and jumping spider Phidippus clarus (Keyserling 1884). After 1 wk, jumping spiders reduced the number of plant bugs. Plants exposed to plant bugs alone were significantly shorter than either control plants or plants exposed to plant bugs and spiders. Chlorophyll concentration did not significantly differ across treatments. We discuss the feasibility of using P. clarus and similar salticids in biocontrol.
... Predicting such outcomes is especially important for biological control, where an introduced predator's or parasitoid's interactions with other natural enemies could inadvertently increase herbivore populations (Rosenheim 1998; Fagan et al. 2002; Van Lenteren et al. 2003). Emergent effects may be " risk enhancing " to the prey if predators kill more prey than expected together than by themselves (Losey and Denno 1998; Swisher et al. 1998), or " risk reducing " if predators kill fewer prey than expected (Spiller 1986; Rosenheim et al. 1993). Emergent multiple predator effects may be trait-or density-mediated. ...
Multiple predator species feeding on a common prey can lead to higher or lower predation than would be expected by simply combining their individual effects. Such emergent multiple predator effects may be especially prevalent if predators share feeding habitat. Despite the prevalence of endophagous insects, no studies have examined how multiple predators sharing an endophytic habitat affect prey or predator reproduction. We investigated density-dependent predation of Thanasimus dubius (Coleoptera: Cleridae) and Platysoma cylindrica (Coleoptera: Histeridae) on a bark beetle prey, Ips pini (Coleoptera: Scolytidae), in a laboratory assay. I. pini utilize aggregation pheromones to group-colonize and reproduce within the stems of conifers. T. dubius and P. cylindrica exploit these aggregation pheromones to arrive simultaneously with the herbivore. Adult T. dubius prey exophytically, while P. cylindrica adults enter and prey within the bark beetle galleries. Larvae of both predators prey endophytically. We used a multiple regression analysis, which avoids confounding predator composition with density, to examine the effects of varying predator densities alone and in combination on herbivore establishment, herbivore reproduction, and predator reproduction. Predators reduced colonization success by both sexes, and decreased I. pini reproduction on a per male and per female basis. The combined effects of these predators did not enhance or reduce prey establishment or reproduction in unexpected manners, and these predators were entirely substitutable. The herbivore's net replacement rate was never reduced significantly below one at prey and predator densities emulating field conditions. Similar numbers of each predator species emerged from the logs, but predator reproduction suffered from high intraspecific interference. The net replacement rate of P. cylindrica was not affected by conspecifics or T. dubius. In contrast, the net replacement rate of T. dubius decreased with the presence of conspecifics or P. cylindrica. Combinations of both predators led to an emergent effect, a slightly increased net replacement rate of T. dubius. This may have been due to predation by larval T. dubius on pupal P. cylindrica, as P. cylindrica develops more rapidly than T. dubius within this shared habitat.
... First, individuals searching for web sites might perceive established webs and avoid building webs nearby. This avoidance behavior may be advantageous if it reduces competition and enhances prey availability for established web owners (Spiller 1986). Second, direct encounters between spiders, including web builders and wolf spiders, could have produced the regularity observed before and after cutting. ...
Understanding the development of spatial patterns in generalist predators will improve our ability to incorporate them into biological control programs. We studied the small-scale spatial patterns of spider webs in alfalfa by analyzing the relationship between web locations over distances ranging from 4 to 66 cm. Using a coordinate-based spatial statistic (O-ring) and assuming a heterogeneous distribution of suitable web sites, we analyzed the impact of cutting and changes in spider abundance on web distribution. We analyzed the influence of small-scale variation in prey availability by comparing web distributions to the pattern of sticky-trap captures of Aphididae and Diptera described by a count-based spatial statistic (SADIE). Cutting of alfalfa reduced the overall density of web-building spiders but had no immediate impact on the spatial distribution of their webs. Availability of aphids was highest before the alfalfa was cut and was clumped at a scale of 66 cm. Spider webs, however, were not clumped at any scale or date. In contrast, webs were regularly distributed at smaller distances (<20 cm) immediately before and after cutting. Because cursorial and web-building spiders were most active during this period, we hypothesize that the development of small-scale regularity in web locations was driven by intraguild interactions. Our results suggest that intraguild interactions contribute to the development of small-scale spatial patterns of spider webs in alfalfa. Variation in prey availability may have more of an influence on web distribution in crops with a different vegetation structure or if patterns are studied at larger spatial scales.
Rivers produce an abundance of aquatic insects that traverse land, where they can have bottom-up effects on predators, who, in turn, can have top-down effects on terrestrial herbivores. This effect can cascade down to plants. These trophic relationships were demonstrated in a field of stinging nettles, Urtica dioica, along a river in Germany. At the shore compared to similar microhabitats 30–60 m away the abundance and biomass of: midges were highest, spiders were also highest, while herbivorous leafhoppers were lowest. At the shore, nettle plants were less damaged by herbivores and thus had less regrowth. Spiders regularly captured both aquatic midges as well as terrestrial leafhoppers and they captured more individuals of both groups at the shore than further away. Midges supported high densities of shore spiders. This was inferred from correlation of distribution and diet in the absence of other environmental gradients. Removal of spiders from experimental plots caused leafhoppers to increase at the shore, causing more plant damage. These effects were not evident at spider-removal sites away from the shore. This demonstrated that spiders depressed leafhoppers and decreased herbivory on plants only at the shore. It is concluded that aquatic insects had a bottom-up effect on spiders and that this subsidy facilitated a top-down effect that cascaded from spiders to leafhoppers to plants. Similar effects would explain the distribution of arthropods along many rivers. Allochthony connects river food webs with shore food webs, making both components essential for each other.
We evaluated the potential for emergent nonlinear effects, of multiple predators on mortality of a, shared prey species by conducting experiments in cages in an old field. We examined interactions among three spider predators, Pisaurina mira, Phidippus rimator, and Rabidosa rabida, and a grasshopper prey Melanoplus femurrubrum. The predators have disparate hunting behaviors and are located in different parts of the vegetation canopy used by the grasshoppers, suggesting the potential for nonlinear effects. We examined the effects of spider species singly and in all possible combinations using a substitutive design in each of two years. Multiple predator effects on grasshopper mortality were generally the average of the corresponding single-species effects,'indicating that the species effects were largely substitutable. This result indicates that it is reasonable to aggregate these predator species into a single functional unit, despite their disparate individual effects on grasshopper prey, when modeling predator-prey interactions for this system.
Mortality rates in insects, including grasshoppers (Acrididae), are often stage- or size-specific. We estimated stage-specific mortality rates for three common grasshopper species from a Nebraska (USA) sandhills grassland (Ageneotettix deorum, Melanoplus sanguinipes and Phoetaliotes nebrascensis), and partitioned the impact due to wandering spider predation from remaining sources. Survivorship was estimated for multiple developmental stages (3rd instar through adult) under experimental conditions that either prevented or permitted predation from free-living, wandering spiders (primarily Schizocosa species). Total stage-specific mortality, including spider predation, examined over the period of single stages was greatest for the youngest stages (91% for 3rd instar, 73% for 4th instar, 63.5% for 5th instar and 30.4% for adults). For the developmental stages considered and averaged for all species, the contribution to total mortality from spider predation over the 10-d period (approximately the length of a developmental stage) ranged from 17% for 3rd instar nymphs to 23% for 4th and 5th instars, and an undetectable level for adults. While spiders may depress grasshopper numbers, contributions from spider predation to grasshopper population dynamics are uncertain.
: Petri dish experiments were conducted to study intraguild predation (IGP) between erigonid spiders (Erigone atra (Blackwall), Oedothorax apicatus (Blackwall), a carabid beetle (Pterostichus melanarius (Ill.) and lacewing, Chrysoperla carnea (Stephens) larvae. Erigonid spiders increased the mortality rates of lacewing larvae to different degrees, depending on the species and sex of spider concerned. The effect of spiders on lacewing larvae was highest (up to nearly 100% mortality) in the absence of alternative prey. In the presence of three or 20 aphids (Sitobion avenae Fab.) female erigonids increased the mortality rates of lacewing larvae compared to controls, but predation on lacewing larvae decreased in the presence of increasing numbers of aphids. Males of O. apicatus caused no significant increase in mortality rate of lacewing larvae in the presence of aphids. Lacewing larvae (L2-larvae and L3-larvae) did not kill erigonid spiders. IGP between the female erigonids E. atra and O. apicatus was not found. P. melanarius fed on lacewing larvae and on erigonid spiders, and E. atra was preferred over O. apicatus. The sex-specific and species-specific IGP rates of spiders on lacewing larvae and the great influence of alternative prey on IGP rate reveal a general problem when data resulting from one sexual stage or one species or one feeding regime are generalized to a whole arthropod group. Moreover, the results suggest that an increase of top predators, such as carabid beetles, which prey only to a limited extent on the pest species itself, may affect natural insect pest control by IGP.
Competitive interaction between two introduced parasitoids of Heliothis armigera (Hb.) i.e. the braconid Cotesia kazak Telenga and the ichneumonid Hyposoter didymator (Thunb.) was studied in the laboratory. C. kazak and H. didymator individually parasitized about 55% H. armigera larvae, the combination of the two parasitoids gave more than 75% parasitism. C. kazak was found to be more effective, when the host was exposed to both parasitoids at the same time, reduced H. didymator population by 69% to 24 h. It is, therefore, better to release these two parasitoids individually in different locations to avoid any possible competitive interaction between the two. No difference in developmental time was observed irrespective of parasitoid sequence.
In order to explore the suitability of using ¹⁵ N as marker in predation studies, a semi‐field test was carried out. This study focused on epigeic polyphagous predators in a wheat field using ¹⁵ N‐marked aphids as prey. The ¹⁵ N‐aphids were released in enclosures. Eight days after their release the whole predator fauna of the enclosures was caught, and predators were analysed for ¹⁵ N‐content.
More than 80% of the predators showed an enriched ¹⁵ N‐content. The ¹⁵ N‐enrichments varied between taxonomic groups, species, sex, and individuals, providing an extensive data set for the analysis of predation. Competition between predators could be inferred, as well as an estimation of the number of consumed aphids. During this experiment, the carabids Platynus dorsalis (Pontoppidan) and Calathus melanocephalus (L.), the staphylinid Philonthus cognatus Stephens, and the spider Oedothorax apicatus (Blackwall) were the most efficient polyphagous predators upon aphids, in agreement with literature data which was based on other methods.
Theory in community ecology often assumes that predator species have similar indirect effects and thus can be treated mathematically as a single functional unit (e.g. guild or trophic level). This assumption is questionable biologically because predator species typically differ in their effects, creating the potential for nonlinearities when they coexist. We evaluated the nature of indirect effects caused by three species of hunting spider predators, singly and in multiple species combinations, on grass and herb plants in experimental old-field food webs. Despite the potential for nonlinearity, indirect effects in different multiple predator combinations consistently did not differ significantly from the respective means of the single species effects. Thus, for this experimental system, the whole was simply the average of the parts. Consequently, models which abstract predator species as single trophic levels would successfully predict indirect effects in this system regardless of the composition of the predator fauna.
The view of terrestrial arthropod communities as potentially exhibiting a mixture of three-and four-trophic-level dynamics creates a new challenge for researchers: the indeterminacy of predator function. Here we evaluate two predictions linking a predator's foraging behavior with its likely ecological role: (1) widely foraging predators may act as effective regulators of sedentary herbivore populations, and (2) sit-and-wait predators are unlikely to regulate sedentary herbivore populations but may act as top predators, consuming widely foraging intermediate predators and allowing herbivore populations to escape from control. We tested these predictions by manipulating the predator community associated with a sedentary herbivore, the spider mite Tetranychus cinnabarinus, feeding on papaya, Carica papayae. The predators included a widely foraging specialist consumer of spider mites, the ladybird beetle Stethorus siphonulus, and a sit-and-wait generalist predator, the tangle-web spider Nesticodes rufipes. The experiments provided support for both predic-tions. The widely foraging predator Stethorus when tested alone was capable of effective suppression of spider mite populations. In contrast, the sit-and-wait predator, Nesticodes, never suppressed spider mites. Instead, Nesticodes consistently increased the population growth rates of spider mites. This effect was most likely due to Nesticodes suppressing populations of the intermediate predator Stethorus. Our results underscore the presence of both three-and four-trophic-level dynamics within this arthropod community and begin to address the challenging problem of the indeterminacy of predator function.
The outcome of competition between Campoletis chlorideae Uchida and Eriborus argenteopilosus (Cameron) (Hymenoptera: Ichneumonidae), two indigenous larval parasitoids of the noctuid pest, Spodoptera litura (Fabricius), was investigated in the laboratory by way of two experiments. In the individual exposure experiment, the host larvae were exposed to the parasitoids either alone or one after the other at different time intervals and were considered to be parasitised when the parasitoid was observed to sting the host larva. When they stung the host larva singly, the parasitism rates by C. chlorideae and E. argenteopilosus was either similar to or higher than the parasitism recorded by each parasitoid in the different combination/interaction treatments. C. chlorideae cocoons were formed from majority of the host larvae, which were stung by both parasitoid species, one after the other, in most oviposition orders and delays between ovipositions. E. argenteopilosus appeared to be the dominant parasitoid only in those treatments where it was the first one to parasitise and the delay in C. chlorideae parasitism was more than 18h. and it never dominated the interactions, when it was the second one to parasitise. This implied that C. chlorideae had an almost consistent advantage over E. argenteopilosus. In the mass exposure experiment, the two parasitoid species (either alone or together) were allowed to forage and parasitise the host larvae in cages. When the two parasitoid species were allowed to forage in the same host patch simultaneously, the performance of C. chlorideae when it was alone was statistically similar to its performance in the presence of E. argenteopilosus. However, E. argenteopilosus performed better when it could forage alone. The results of both experiments revealed that C. chlorideae was the more competitive of the two species.
We evaluated the influence of intraguild predation among generalist insect predators on the suppression of an herbivore, the
aphid Aphis gossypii, to test the appropriateness of the simple three trophic level model proposed by Hairston, Smith, and Slobodkin (1960). We
manipulated components of the predator community, including three hemipteran predators and larvae of the predatory green lacewing
Chrysoperla carnea, in field enclosure/exclosure experiments to address four questions: (1) Do generalist hemipteran predators feed on C. carnea? (2) Does intraguild predation (IGP) represent a substantial source of mortality for C. carnea? (3) Do predator species act in an independent, additive manner, or do significant interactions occur? (4) Can the experimental
addition of some predators result in increased densities of aphids through a trophic cascade effect? Direct observations of
predation in the field demonstrated that several generalist predators consume C. carnea and other carnivorous arthropods. Severely reduced survivorship of lacewing larvae in the presence of other predators showed
that IGP was a major source of mortality. Decreased survival of lacewing larvae was primarily a result of predation rather
than competition. IGP created significant interactions between the influences of lacewings and either Zelus renardii or Nabis predators on aphid population suppression. Despite the fact that the trophic web was too complex to delineate distinct trophic
levels within the predatory arthropod community, some trophic links were sufficiently strong to produce cascades from higher-order
carnivores to the level of herbivore population dynamics: experimental addition of either Z. renardii or Nabis predators generated sufficient lacewing larval mortality in one experiment to release aphid populations from regulation by
lacewing predators. We conclude that intraguild predation in this system is wide-spread and has potentially important influences
on the population dynamics of a key herbivore.
The nature and relative strengths of intra versus interspecific interactions among foraging ladybeetle larvae were studied experimentally by measuring short-term growth rates of predators and reductions in population sizes of prey in laboratory microcosms. In these microcosms, ladybeetle larvae foraged singly or as conspecific or heterospecific pairs, for pea aphids on bean plants over a two-day period. Similarly sized third instar larvae ofHippodamia convergens andH. tredecimpunctata, H. convergens andH. sinuata, andH. convergens andCoccinella septempunctata, were tested in experiments designed to ensure that paired larvae experienced moderate competition. Interspecific competition in these experiments did not differ significantly from intraspecific competition, in that an individual's weight gain did not depend on whether its competitor was heterospecific or conspecific. Furthermore, aphid populations were reduced equally by heterospecific and conspecific pairs. These results suggest that there is little or no difference between intra and interspecific interactions among larvae of these ladybeetles when two similarly sized individuals co-occur on a host plant. Thus, the species diversityper se of assemblages of ladybeetle larvae may have little influence over the short term on the reduction of aphid populations by ladybeetle predation.
A 5-year-field experiment was performed in a meadow to test the effect of strip-management (small unmown strips alternating with broad mown strips, Fig. 1) on the abundance and composition of arthropods. The species number and density of most predator groups increased from year to year. The succession (parallel to the development of the unmown strips) favoured more specialized species, so that the initial pioneer species become less abundant in consecutive years. In spiders, this succession leads from a dominance of Linyphiidae to a dominance of Lycosidae; the spider biomass increases and probably predator pressure by spiders is augmented. The stability of the predator community (measured as the variance of their frequency in successive years) is higher than that of the phytophagous groups. Under strip-managed conditions the abundance (activity density) of most arthropod groups decreases by an average of ca. 12%. The trophic levels, however, are affected to different extents and strong species-specific preferences were found as well. These combined effects lead to constant increase in the ratio of predacious and parasitic to phytophagous insects in the strip-managed area and probably lead also to an increase of the predator pressure facing phytophagous insects. Strip-management is discussed as an important technique among integrated methods for the biological control of pests.
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