Generalist Arthropod Predators Research Articles

Prey killing rate of a generalist predator may be enhanced by macronutrient manipulation

Generalist arthropod predators forage not only to gain energy and nutrients, but also to obtain a balanced intake of macronutrients (the intake target). We test two opposite hypotheses concerning the predation rate of nutritionally imbalanced predators: It will increase (1) if the prey is rich in macronutrients that the predator is short of, or (2) if the prey is low in macronutrients that the predator is short of. We used the wolf spider Pardosa amentata (Clerck) as the predator and nutritionally manipulated Drosophila melanogaster Meigen as prey. We completed a full factorial experiment with eight treatment groups, in which we measured predation, consumption and prey utilization of high-protein (HP) and high-lipid (HL) flies by spiders that were previously treated with either HP- or HL-flies for two or six days. The results supported hypothesis 2. Whether spiders had been previously fed HP-or HL-flies, those that were tested against the same type of fly killed more than those tested against the opposite type of fly. A likely explanation for this result is that the predator will be unable to reach its macronutritional intake target by continued feeding on the same prey. It will stay nutritionally imbalanced and continue to catch prey in an attempt to redress its imbalance. In natural systems, predation rates may thus be increased by the widespread mismatch between predators’ nutritional demands and what is available in prey. In practical biological control, it suggests a beneficial effect of feeding the predator prior to release with the pest it is intended to control.

Predator–prey interactions in the Arctic: DNA metabarcoding reveals that nestling diet of snow buntings reflects arthropod seasonality

AbstractTundra arthropods are of considerable ecological importance as a seasonal food source for many arctic‐breeding birds. Dietary composition and food preferences are rarely known, complicating assessments of ecological interactions in a changing environment. In our field study, we investigated the nestling diet of snow buntings (Plectrophenax nivalis (L., 1758)) breeding in Svalbard. We collected fecal samples from 8‐day‐old nestlings and assessed dietary composition by DNA metabarcoding. Simultaneously, the availability of potential prey arthropods was measured by pitfall trapping. Molecular analyses of nestling feces identified 31 arthropod taxa in the diet, whose proportions changed throughout the brood‐rearing period. Changes in nestling diet matched varying abundances and emergence patterns of the tundra arthropod community. Snow buntings provisioned their offspring mainly with Diptera (true flies) based on both presence/absence and relative read abundance of diet items. At the beginning of the season in June, Chironomidae (nonbiting midges) and the scathophagid fly Scathophaga furcata (Say, 1823) dominated the diet, whereas the muscid fly Spilogona dorsata (Zetterstedt, 1845) dominated the diet later in July. When accounted for availability, muscid flies were selected positively among the most often provisioned food taxa. Our study demonstrates the ecological role of the snow bunting as a generalist arthropod predator and highlights DNA metabarcoding as a noninvasive technique for diet analyses with high taxonomical precision if sufficient DNA‐sequence libraries are available.

Extrinsic and intrinsic musculature of the raptorial forelegs in Mantodea (Insecta) in the light of functionality and sexual dimorphism.

Prehensile raptorial forelegs are prey capturing and grasping devices, best known for praying mantises (Mantodea) within insects. They show strong morphological and behavioral adaptations towarda lifestyle as generalist arthropod predators. In the past, few species of Mantodea were investigated, concerning morphological variability of the raptorial forelegs. Especially the knowledge of foreleg anatomy in the light of functional and comparative morphology is scarce. Our comparative approach is based on the, for arthropods very common, "female-biased sexual size dimorphism"(SSD) that occurs in almost every Mantodea species. Within Mantodea, this SSD is likely leading to a shift of the exploited ecological niche between male and female individuals due to changes in, for example, the possible prey size; which might be reflected in the chosen ecomorphs. In this context, we analyzed the musculature of the raptorial forelegs of female and male specimens in five different species with varying SSD, using high-resolution microcomputed tomography and dissection. We were able to confirm the presence of 15 extrinsic and 15 intrinsic muscles-including one previously undescribed muscle present in all species. Thus, presenting a detailed description and illustrative three-dimensional anatomical visualization of the musculature in Mantodea. Interestingly, almost no observable differences were found, neither between species, nor between the sexes. Furthermore, we homologized all described muscles, due to their attachment points, to the comprehensive nomenclature established by Friedrich and Beutel (2008), discussed potential functionality of the muscles and possible homologies to the neuropteran Mantispa styriaca (Büsse et al., 2021) and the newly introduced leg nomenclature by Aibekova et al. (2022). By elucidating the anatomy, particularly in the context of functionality and SSD, our results complement previous knowledge of the raptorial forelegs, and facilitate a better understanding of the underlying biomechanical system of the predatory strike, and ultimately, a future comparison to other insect taxa.

Intercropping shifts the balance between generalist arthropod predators and oilseed pests towards natural pest control

Pest management in intensive crop production currently underutilizes natural biological control, and frequently results in pesticide application. Intercropping modifies physical and ecological conditions in the field and alters the predator-prey dynamics to potentially benefit generalist arthropod predators. We investigated the assemblages of ground-dwelling arthropod predators and crop pests of spring turnip rape (Brassica rapa L. ssp. oleifera) and faba bean (Vicia faba L.) in a replicated two-year field experiment. Pitfall traps and pan traps were used to sample arthropod predators and pests. Arthropod assemblages were compared between intercropping and monocropping systems to illustrate the changes. Intercropping was associated with lower abundance of turnip rape pests compared with monoculture. The total abundance of ground-dwelling predators did not differ between cropping systems. Carabid beetles (Coleoptera: Carabidae) and spiders (Araneae) were the dominant generalist predator taxa. Faba bean monoculture supported the highest abundance of harvestmen (Opiliones) and the lowest abundance of ants (Hymenoptera: Formicidae). The turnip rape monoculture had the highest abundance of spiders in the first year but not in the second. The abundance and species assemblage of carabids indicated a response to season progress but not to cropping system. The abundance of turnip rape pests reflected host crop proportions in each cropping system. Because the cropping method had no significant impact on predator abundance, intercropping potentially facilitated natural biological control resulting from a higher ratio of ground-dwelling predators to pests. Differential within-season dynamics among abundant predator taxa also implied a temporal shift in predation characteristics, and hence, vulnerability of crop production to pest injuries. To utilize natural biological control more effectively at the field scale, intercropping with no shared pests between crops, minimal chemical pest control, and heterogeneous agricultural landscapes are needed.

Conifers and non-native tree species shift trophic niches of generalist arthropod predators in Central European beech forests

BackgroundFunctional diversity is vital for forest ecosystem resilience in times of climate-induced forest diebacks. Admixing drought resistant non-native Douglas fir, as a partial replacement of climate-sensitive Norway spruce, to native beech forests in Europe appears promising for forest management, but possible consequences for associated biota and ecosystem functioning are poorly understood. To better link forest management and functional diversity of associated biota, we investigated the trophic niches (∆13C, ∆15N) of epigeic generalist predators (spiders and ground beetles) in mixed and pure stands of European beech, Norway spruce and non-native Douglas fir in north-west Germany. We assessed the multidimensional niche structure of arthropod predator communities using community-based isotopic metrics.ResultsWhilst arthropod ∆13C differed most between beech (high ∆13C) and coniferous stands (low ∆13C), ∆15N was lowest in non-native Douglas fir. Tree mixtures mitigated these effects. Further, conifers increased isotopic ranges and isotopic richness, which is linked to higher canopy openness and herb complexity. Isotopic divergence of ground beetles decreased with Douglas fir presence, and isotopic evenness of spiders in Douglas fir stands was lower in loamy sites with higher precipitation than in sandy, drier sites.ConclusionsWe conclude that tree species and particularly non-native trees alter the trophic niche structure of generalist arthropod predators. Resource use and feeding niche breadth in non-native Douglas fir and native spruce differed significantly from native beech, with more decomposer-fueled and narrower feeding niches in beech stands (∆13C, isotopic ranges and richness). Arthropod predators in non-native Douglas fir, however, had shorter (∆15N) and simplified (isotopic divergence) food chains compared to native forest stands; especially under beneficial abiotic conditions (isotopic evenness). These findings indicate potential adverse effects of Douglas fir on functional diversity of generalist arthropod predators. As tree mixtures mitigated differences between beech and conifers, mixed stands including (non-native) conifers constitute a promising compromise between economic and conservational interests.

Licorice strips enhance predator-mediated biological control in China's cotton crop.

Habitat management such as field- or farm-level diversification can conserve arthropod natural enemies, enhance biological pest control and lower (or suspend) insecticide use in agricultural crops. These approaches however have been underexploited to manage the aphid Aphis gossypii in cotton cropping systems of Xinjiang, China. In this study, we investigated whether the presence of licorice (Glycyrrhiza uralensis) at the field edge benefits generalist predator abundance and aphid biological control in local cotton crops. Field trials during 2020 and 2021 showed that licorice strips enhanced the in-field abundance of generalist predators (primarily ladybeetles) 2.2-4.3 fold during early season, i.e. initial growth before A. gossypii peak infestation pressure. During peak outbreak conditions in July, treatment fields with licorice strips experienced a respective 17.5-61.2% lowered aphid density and 12.3-14.6-fold higher predator-to-aphid abundance ratio (PAR) than control fields. In late season (aphid decline phase) of either year, cotton fields with licorice strips also attained a respective 4.7-9.9 fold higher PAR. Exclusion cage assays quantitatively assessed predator-mediated A. gossypii biological control and the relative contribution of licorice strips. The biocontrol services index (BSI) was 2.8 times (2020) and 1.4 times (2021) higher at 5m distances from the licorice strip as compared to control fields. Licorice strips in the immediate vicinity of cotton fields benefit generalist arthropod predators and improve aphid biological control throughout the cotton cropping season. These findings help to integrate habitat management within integrated pest management (IPM) frameworks in the biggest cotton production region of China. © 2022 Society of Chemical Industry.

Intercropping Shifts the Balance between Generalist Arthropod Predators and Crop Pests Towards Natural Pest Control

Intercropping Shifts the Balance between Generalist Arthropod Predators and Crop Pests Towards Natural Pest Control

Dietary niche breadth of endemic and introduced anurans (Amphibia: Anura) in Lombok, Lesser Sunda Islands– Indonesia

Anurans are important organisms as components of faunal community structure in ecosystems because of their roles as secondary and tertiary consumers in food webs. Anurans are opportunistic organisms that will consume any resources in their habitat. In this study, we dissected thirty-nine specimens of anurans from Museum Universitas Mataram (MUM) reference collection, it consists by three endemic (Ingerophrynus biporcatus, Limnonectes dammarmani and L. kadarsani) and one introduced species (Duttaphrynus melanostictus) of anurans. These reference collections were collected by authors during herpetofauna survey at Pusuk Forest, western Lombok in 2018. Based on stomach content analysis, both endemic and introduced anurans are generalist arthropod predators where hymenoptera, coleoptera, orthoptera and chilopoda are the most important food. In this study, we found positive correlations between body size and dietary niche breadth in which each anuran species has a high overlap of dietary niches. Anurans with large body size have a variety of prey than the small one.

Pest consumption by generalist arthropod predators increases with crop stage in both organic and conventional farms

AbstractBiocontrol agents are critical for pest management in sustainable agriculture. Generalist arthropod predators may hold a great potential as biocontrol agents because they are ubiquitous and consume pests in agroecosystems. However, their diet composition over the entire crop season has rarely been quantified, which hinders our ability to assess their biocontrol potential in real field conditions that foster temporal dynamics of pest and alternative prey populations. To fill this knowledge gap, we surveyed arthropod communities over crop stages in organic and conventional rice farms (n = 7 each) and used stable isotope analysis (δ13C and δ15N) to quantify the diet composition of generalist arthropod predators over time. We aimed to (1) examine the resource partitioning (trophic niches) in these predators, (2) quantify these predators’ diet composition from potential prey sources (rice herbivores, tourist herbivores, and detritivores), and (3) investigate the effects of farm type (organic/conventional) and crop stage (tillering/flowering/ripening stage) on pest (rice herbivore) consumption by the predators. The results show that generalist predators in both organic and conventional farms shifted trophic niches over the crop season and consumed a higher percentage of rice herbivores at late than at early crop stages (e.g., 90–93% at ripening vs. 34–55% at tillering), suggesting an increasing biocontrol value over time regardless of farm type. Surprisingly, generalist predators consumed higher proportions of rice herbivores in conventional than organic farms at tillering and flowering stages, highlighting their underappreciated potential as biocontrol agents in conventional farms. These results demonstrate that although generalist arthropod predators do consume non‐pest alternative prey, they have a high biocontrol potential (per capita pest consumption) in both organic and conventional rice farms. We encourage modern agriculture to develop techniques to support robust populations of these predators and the ecosystem services that they provide.

Plant Mediated Interactions: Lower Sawfly Survival on Pines Previously Browsed by Moose

Insect herbivore performance and arthropod communities can be affected by mammalian grazing and browsing via altered plant communities and vegetation structure. Far less is known about whether changes to plant architecture can cause similar effects. Browsing generated changes to within plant architecture could potentially have large consequences for arthropod communities, herbivore survival and eventually damage to plants. This study investigates plant-mediated effects of ungulate browsing on arthropod predator communities and on the survival of herbivorous insects. More specifically we studied how different levels of ungulate browsing (1) influenced the arthropod predator community on Scots pine (Pinus sylvestris) and (2) affected the survival of the European pine sawfly (Neodiprion sertifer). We related these response variables to browsing-inflicted changes in pine architecture. An observational study of generalist arthropod predators on pine trees revealed a trend toward a quadratic response of ants to browsing intensity—i.e., a higher abundance of ants on moderately browsed trees and lower abundance on intensively browsed trees. A field survey of sawfly larvae revealed a 19% lower larval survival on browsed compared to un-browsed pines, but no difference in survival comparing pines with moderate and high intensity of browsing. A structural equation model revealed that moose generated changes to pine architecture had only a small effect on sawfly larval survival, suggesting additional mediating pine traits affected by browsing. We conclude that insect survival can be altered by ungulate browsing, which could affect damage levels.

Insights Into the Establishment of Introduced Species Using Coccinellines (Coleoptera: Coccinellidae) as a Model System

Species introductions occur around the world both inadvertently and deliberately (typically for conservation, agriculture or fisheries). However, not all introduced species become established. Understanding the factors that affect the establishment success of introduced species will help us improve species introductions for biocontrol and conservation purposes. Here we argue that important generalist arthropod predators, the Coccinellini ladybirds (Coleoptera: Coccinellidae), are an ideal taxon for investigating the establishment process of introduced species. Coccinellini are introduced accidently via plant exports, as well as deliberately as biocontrol agents to reduce agricultural pests, and a few have become invasive species. Here, using work from invasive biology and biocontrol systems, we categorize the factors affecting the successful establishment of introduced species. These factors are 1) invasiveness of the species, 2) invasibility of the recipient ecosystem and 3) stochastic events that occur after the introduction. We review how factors such as diet and competition, dispersal ability, propagule population, disturbances and climate change can be studied within these three categories to better predict the establishment success of introduced ladybirds. Our review highlights that our current understanding of the differences between successful and unsuccessful species establishments is limited. To address this, we need direct comparisons of dispersal ability and both interspecific and intraspecific variation in ladybirds. We conclude that studies of ladybirds will help to develop theories that better characterize and predict establishment success and invasive potential.

Ants Increase Cloverworm Herbivory Via Nonconsumptive Pathways

Generalist arthropod predators often exhibit a range of intraguild interactions reducing their potential efficacy as biological control agents. These interactions may include consumptive or nonconsumptive effects that mediate the impacts of herbivores. We examined interactions among 2 generalist predators, the striped lynx spider (Oxyopes salticus Hentz; Araneae: Oxyopidae) and an ant (Lasius neoniger Emery; Hymenoptera: Formicidae), and a herbivore, the green cloverworm (Hypena scabra F.; Lepidoptera: Erebidae), all prevalent in central Kentucky soybean agroecosystems. We hypothesized that individual predator treatments would reduce green cloverworm survival and resultant leaf damage, but that predators would interfere with each other when both were present. To study these interactions, field cages containing potted soybeans were used to examine 8 treatment combinations (control, cloverworm, spider, ant, spider + cloverworm, ant + cloverworm, ant + spider, and ant + spider + cloverworm). When proportional leaf damage was compared, spider, ant + spider, and spider + cloverworm treatments had significantly less damage than the ant, ant + cloverworm, and ant + spider + cloverworm treatments. Spider presence tended to decrease plant damage while ant presence significantly increased damage. No differences among treatments were found for either spider or cloverworm recovery, indicating potential nonconsumptive effects of ants that may include compensatory feeding. We found that generalist predators, such as L. neoniger, can inhibit biological control due to nonconsumptive interactions even when the same species in a different system provides substantial levels of pest suppression. Resumen Los depredadores de artropodos generalistas a menudo exhiben un rango de interacciones intra-gremial (entre el grupo depredador) reduciendo su eficacia potencial como agentes de control biologico. Estas interacciones pueden incluir efectos consuntivos o no consuntivos que median los impactos de los herbivoros. Examinamos las interacciones entre dos depredadores generalistas, la arana lince rayada (Oxyopes salticus Hentz; Araneae: Oxyopidae) y una hormiga (Lasius neoniger Emery; Hymenoptera: Formicidae), y un herbivoro, el gusano verde de trebol (Hypena scabra F.; Lepidoptera: Erebidae), todos prevalentes en los agroecosistemas de soja del centro del estado de Kentucky. Presumimos que los tratamientos de depredadores individuales reducirian la sobrevivencia del gusano verde de trebol y el dano resultante en las hojas, pero que los depredadores interferirian entre si cuando ambos estuvieran presentes. Para estudiar estas interacciones, se utilizaron jaulas de campo que contenian soja en maceta para examinar 8 combinaciones de tratamiento (el control, el gusano verde de trebol, arana, hormiga, arana + el gusano verde de trebol, hormiga + el gusano verde de trebol, hormiga + arana, y hormiga + arana + el gusano verde de trebol). Cuando se comparo el dano proporcional de las hojas, los tratamientos de arana, hormiga + arana y arana + el gusano verde de trebol tuvieron un dano significativamente menor que los tratamientos de hormiga, hormiga + el gusano verde de trebol y hormiga + arana + el gusano verde de trebol. La presencia de las aranas tiende a disminuir el dano a las plantas, mientras que la presencia de las hormigas aumenta significativamente el dano. No se encontraron diferencias entre los tratamientos para la recuperacion de la arana o el gusano verde de trebol, lo que indica posibles efectos no consuntivos de las hormigas que pueden incluir la alimentacion compensatoria. Descubrimos que los depredadores generalistas, como L. neoniger, pueden inhibir el control biologico debido a interacciones no consumidoras, incluso cuando la misma especie en un sistema diferente proporciona niveles sustanciales de supresion de plagas. Key Words: Hypena scabra; field cage; food web; Lasius neoniger; Oxyopes salticus View this article in BioOne

Subsidy type and quality determine direction and strength of trophic cascades in arthropod food webs in agroecosystems

Abstract The subsidy hypothesis states that communities receiving nutrient subsidies will demonstrate top‐down trophic cascades where predators indirectly increase plant biomass. This has been both confirmed and refuted, which might depend on whether the subsidy has mainly targeted the plant or the detrital food web compartment, and on the subsidy quality. This is particularly poorly understood for terrestrial communities such as heavily subsidized agroecosystems. Using cages covering 4 m2 of ground in a long‐term agricultural fertilization experiment, we tested whether subsidies targeting the detrital soil mesofauna compartment with organic fertilizers, or the plants with mineral fertilizer, impacted the direction and strength of trophic cascades in an arthropod–plant food web. We expected top‐down controls of generalist arthropod predators (spiders, ground and rove beetles) on aphid densities to be stronger in organically fertilized plots due to enhanced alternative prey availability in the soil. Bottom‐up control from barley quality on aphids was anticipated to be stronger in the mineral treatments. We examined how the quality (decomposability) of the organic subsidy governed the cascades by comparing treatments with labile (manure) and recalcitrant (hay) organic matter. Top‐down forces dominated in food webs receiving organic subsidies, while bottom‐up forces dominated under mineral fertilization. A high‐quality, easily degradable organic subsidy propagated faster through the food chain, leading to a top‐down trophic cascade with generalist predators having a positive effect on plant biomass in the labile but not in the recalcitrant organic treatment. Synthesis and applications. Management of agricultural soils that bolster the soil mesofauna, for example adding organic fertilizers, has potential to increase top‐down biological control by naturally occurring generalist arthropod predators. Our research demonstrates how barley biomass can be enhanced in manure treatment in the presence of arthropod predators to a level comparable to that of mineral fertilizer.

Predator-Prey Interactions and Eavesdropping in Vibrational Communication Networks

Due to human perceptional bias in favour of air-borne sounds, substrate-borne vibrational signalling has been traditionally regarded as a highly specialized, inherently short-range and, consequently, a private communication channel, free from eavesdropping by sexual competitors and predators. In this review, we synthesise current knowledge pertinent to the view that most animals live in a rich vibratory world, where vibrational information is available to unintended receivers. In recent years, we realized that vibrational signalling is one of the oldest and taxonomically most widespread forms of communication by mechanical waves and that receptors detecting substrate vibrations are ubiquitous. In nature, substrate vibrations are reliable source of information readily available to all members of the animal community able to detect them. Viewing vibrational communication in more relevant ecological context reveals that animals relying on substrate vibrations live in complex communication networks. Long evolutionary history of this communication channel is reflected in varied and sophisticated predator-prey interactions guided by substrate-borne vibrations. Eavesdropping and exploitation of vibrational signals used in sexual communication have been so far largely neglected; however, existing studies show that generalist arthropod predators can intercept such signals emitted by insects to obtain information about prey availability and use that information when making foraging decisions. Moreover, males which advertise themselves for longer periods than females and with vibrational signals of higher amplitude face higher predation risk. It is likely that eavesdropping and exploitation of vibrational signals are major drivers in the evolution taking place in the vibratory world and we believe that studies of interspecific interactions guided by substrate vibrations will, in the future, offer numerous opportunities to unravel mechanisms that are central to understanding behaviour in general.

Predation on stink bugs (Hemiptera: Pentatomidae) in cotton and soybean agroecosystems.

Stink bugs (Hemiptera: Pentatomidae) are significant pests of cotton and soybeans in the southeastern United States with annual control costs exceeding $14 million in these crops. Three of the most prominent stink bug pests are the southern green (Nezara viridula), brown (Euschistus servus) and green (Chinavia hilaris) stink bugs. To determine trophic linkages between generalist arthropod predators and these pests, species-specific 16S molecular markers were designed and used to detect the presence of prey DNA in predator gut-contents. Over 2700 predators were collected over two growing seasons in cotton and soybean in southern Georgia in 2011 and 2012 and screened for stink bug DNA. Trophic linkages were analyzed relative to prey availability, crop type and field location. The frequency of stink bug DNA in predator guts was negligible on E. servus (0.23%) and C. hilaris (0.09%). Overall gut content detection of N. viridula was 3.3% and Geocoris sp. (Hemiptera: Geocoridae), Orius sp. (Hemiptera: Anthocoridae) and Notoxus monodon (Coleoptera: Anthicidae) were the primary predators. This contrasts with previous studies that reported a much more diverse suite of predators consuming stink bugs with much higher frequency of gut-content positives. The discrepancy between studies highlights the need for replicating studies in space and time, especially if the goal is to implement effective and durable conservation biological control in integrated pest management.

Quantifying Conservation Biological Control for Management of Bemisia tabaci (Hemiptera: Aleyrodidae) in Cotton.

Conservation biological control can be an effective tactic for minimizing insect-induced damage to agricultural production. In the Arizona cotton system, a suite of generalist arthropod predators provides critical regulation of Bemisia tabaci Gennadius (MEAM1) (Hemiptera: Aleyrodidae) and other pests. Arthropod predator and B. tabaci populations were manipulated with a range of broad-spectrum and selective insecticide exclusions to vary predator to prey interactions in a 2-yr field study. Predator to prey ratios associated with B. tabaci densities near the existing action threshold were estimated for six predator species found to be negatively associated with either adult and/or large nymphs of B. tabaci [Misumenops celer (Hentz) (Araneae: Thomisidae), Drapetis nr divergens (Diptera: Empididae), Geocoris pallens Stäl (Hemiptera: Geocoridae), Orius tristicolor (White) (Hemiptera: Anthocoridae), Chrysoperla carnea s.l. (Neuroptera: Chrysopidae), and Collops spp. (Coleoptera: Melyridae)] with the first three most consistently associated with declining B. tabaci densities. Ratios ranged from 1 M. celer per 100 sweeps to 1 B. tabaci adult per leaf to 44 D. nr. divergens per 100 sweeps to 1 large nymph per leaf disk. These ratios represent biological control informed thresholds that might serve as simple-to-use decision tool for reducing risk in the current B. tabaci integrated pest management strategy. The identification of key predators within the large, flexible food web of the cotton agro-ecosystem and estimation of predator to B. tabaci ratios clarifies the role of key predators in B. tabaci suppression, yielding potential decision-making advantages that could contribute to further improving economic and environmental sustainability of insect management in the cotton system.

Secondary crops and non-crop habitats within landscapes enhance the abundance and diversity of generalist predators

An agricultural landscape is usually composed of multiple crops and non-crop habitats, and many studies have examined the effects of main crops and non-crop habitats on arthropod communities. However, secondary crops are also important features in argoecosystems, but how they affect generalist arthropod predators in an agricultural landscape has rarely been considered, especially in landscape dominated by small-scale farming. In this study, we applied a principal component analysis to interpret the landscape composition, and we performed a multiple regression analysis basing on Akaike’s information-theoretic selection criterion to assess the effects of secondary crops (other crops besides maize and cotton) as well other landscape component factors (e.g., landscape diversity, non-crop habitats) on the abundance and diversity of generalist predators in Bt cotton fields, across multiple spatial scales in 49 study sites covering at least 600 km2 in northern China. We found that a high proportion of secondary crops significantly enhanced the abundances of lacewings and vegetation-dwelling spiders within a 0.5 km radius, and an increasing proportion of urban habitats supported a high abundance of these spiders, in contrast to the negative effect that high landscape diversity had on spider abundance. However, we failed to find a significant landscape variable response on the abundances of lady beetles and Orius spp. Furthermore, high proportions of both non-crop habitats and urban areas enhanced hoverfly abundance at a 1.5 km radius, while a high proportion of urban areas also supported high diversity but a low dominant species concentration of the predator community at the 2 km scale. Our results suggest that predator abundance and community structure diversity may benefit from secondary crops, non-crop habitats and urban areas in agricultural landscapes, and these habitats and areas will improve the potential ecosystem services of these predators in a pest management program.

Habitat heterogeneity induces rapid changes in the feeding behaviour of generalist arthropod predators.

The “habitat heterogeneity hypothesis” predicts positive effects of structural complexity on species coexistence. Increasing habitat heterogeneity can change the diversity (number of species, abundances) and the functional roles of communities. The latter, however, is not well understood as species and individuals may respond very differently and dynamically to a changing environment.Here, we experimentally test how habitat heterogeneity affects generalist arthropod predators, including epigaeic spiders, carabid and staphylinid beetles, under natural conditions by assessing their diversity and directly measuring their trophic interactions (which provide a proxy for their functional roles). The experiment was conducted in spring barley fields in Southern Sweden where habitat heterogeneity was manipulated by increasing within‐field plant diversity.Increased habitat heterogeneity triggered rapid changes in the feeding behaviour of generalist predators characterized by lower trophic specialization at both network (H2’, degree of interaction specialization in the entire network) and species level (d’, degree of interaction specialization at the species level). We presume that this is because spatial separation resulted in relaxed competition and allowed an increased overlap in resources used among predator species. Predators collected from heterogenous habitats also showed greater individual‐level dietary variability which might be ascribed to relaxed intraspecific competition.Our results provide conclusive evidence that habitat heterogeneity can induce rapid behavioural responses independent of changes in diversity, potentially promoting the stability of ecosystem functions. A plain language summary is available for this article.

The Quality of Nonprey Food Affects Cannibalism, Intraguild Predation, and Hyperpredation in Two Species of Phytoseiid Mites.

Generalist arthropod predators not only prey on herbivores but also may engage in competitive interactions by attacking and consuming conspecifics (cannibalism) or other predators (intraguild predation [IGP] and hyperpredation). These types of interactions are quite common among predators used in biological control. Although there is evidence that nonprey food relaxes cannibalism and IGP, there is little information regarding the impact of the quality of the nonprey food. Herein, we examined how pollen of different nutritional quality (pine, narrow-leaf cattail, or apple) impacted 1) the cannibalism by females of Euseius stipulatus (Athias-Henriot) (Acari: Phytoseiidae) on conspecific larvae, 2) the reciprocal predation between gravid females of E. stipulatus or Iphiseius degenerans (Berlese) (Acari: Phytoseiidae) and heterospecific larvae, and 3) the predation of E. stipulatus on the eggs of the aphid predator Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae). E. stipulatus cannibalism was significantly reduced in the cattail pollen treatment, whereas in the pine pollen it did not significantly differ from control (no food). Predation between I. degenerans and E. stipulatus was significantly reduced in the cattail pollen treatment as compared to the control treatment. Finally, predation of E. stipulatus on A. aphidimyza eggs was significantly reduced when cattail or apple pollen was provided compared to the pine pollen or control treatments. These results suggest that cattail or apple pollen is suitable for mitigating negative interactions among generalist predatory mites used in biological control.

Acceptability ofDiorhabda carinulata, an Introduced Biological Control Agent ofTamarix, as Prey for Selected Resident Native Arthropod Predators

Although biological control agents are imported without the constraints exerted by their native natural enemies, many native, generalist arthropod predators might use the new food source after release in the field. Predation by native arthropods is a potential obstacle to establishment of Diorhabda spp. as a biological control agent against saltcedar, Tamarix spp. Arboreal predaceous insects were surveyed at the Great Salt Plains National Wildlife Refuge to identify possible predators that could affect establishment of the northern tamarisk beetle, Diorhabda carinulata (Desbrochers), in Oklahoma. Results of the survey showed that 57% of the arthropods were represented by five insects, Zelus tetracanthus (Stal) (Hemiptera: Reduviidae) (21%); several species of Chrysoperla (Neuroptera: Chrysopidae) (11%); the insidious flower bug, Orius insidiosus (Say) (Hemiptera: Anthocoridae) (10%); Collops quadrimaculatus (F.) Coleoptera: Melydridae) (8%); and the sevenspotted lady beetle, Coccinella septempunctata L. (Coleoptera: Coccinellidae) (6%), in saltcedar stands. No-choice feeding studies demonstrated that eggs and larvae of D. carinulata were accepted prey for larvae of Chrysoperla rufilabris (Burmeister) and sevenspotted lady beetle adults but not larvae. Northern tamarisk beetle larvae were accepted prey for Z. tetracanthus.