Molecular Gut Content Analysis Research Articles

Different groups of ground‐dwelling spiders share similar trophic niches in temperate forests

Generalistic interactions between predator and prey may vary with ecosystem type, predator traits, and prey traits, but the interplay of these factors has not been assessed in ground food webs. We investigated trophic interactions of ground‐dwelling spiders across eight forests in European Russia associated with body size, hunting strategy, microhabitat specialization, potential prey type, potential prey population density, and forest type (coniferous vs. broadleaved). We analyzed 128 individual spiders, including juveniles, all identified to the family level with two complementary methods: molecular gut content analysis, and stable isotope analysis of carbon and nitrogen. The results suggest that feeding frequency of spiders is affected by predator body size and by selection of certain prey type. Stable isotope analysis showed similar trophic niches among spider families, varying moderately with forest type. Larger spiders had higher Δ13C values than smaller ones, but similar Δ15N values, suggesting that different size classes of spiders belong to different food chains. Results based on stable isotope and molecular gut content analyses were weakly linked, indicating them targeting different trophic niche dimensions. At least for the group‐level interactions, family identity and hunting strategy of predator has little predictive power while predator body size and prey traits affected trophic niche dimensions calling for future studies in this direction. Large spiders feed more and rely on different basal resources than small spiders, suggesting that including small species and juveniles provides a more comprehensive picture of food web organization.

Estimation of movement from insectary plants to crop plants in Orius bugs (Heteroptera: Anthocoridae) by molecular gut content analysis

The introduction of insectary and banker plants is widely used in agroecosystems to improve the survival and reproduction of natural enemies of pest arthropods. Natural enemies that are attracted to and/or maintained on insectary plants need to move from the insectary plants to crop plants to suppress pest populations effectively. In many cases, however, direct evidence supporting the migration of natural enemies is lacking. To investigate the movement of Orius bugs (Hemiptera: Anthocoridae), which are efficient zoophytophagous predators used in biological control, we performed gut content analyses based on DNA markers. Specific PCR primers were designed to detect the DNA of the insectary plant, Scaevola aemula. We also carried out gut content analyses using prey insect DNA markers to estimate Orius bugs’ predation spectrum. DNA of the insectary plant was detected in the abdomen of Orius bugs collected on eggplant leaves, suggesting that Orius bugs had consumed food resources from the insectary plants and relocated to the crop plants. DNA of three prey insect species—two thrips species, Thrips palmi and Frankliniella intonsa, and cotton aphid, Aphis gossypii—was detected in Orius bugs in the eggplant field, indicating that Orius bugs preyed on them.

Use of Molecular Gut Content Analysis to Decipher the Range of Food Plants of the Invasive Spotted Lanternfly, Lycorma delicatula.

Spotted lanternfly, Lycorma delicatula (Hemiptera: Fulgoridae), is an introduced highly invasive insect pest in the US that poses a significant risk to forestry and agriculture. Assessing and predicting plant usage of the lanternfly has been challenging, and little is known regarding the lanternfly nymph association with its host plants. In this study, we focused on: (a) providing a protocol for using molecular markers for food plant identification of L. delicatula; (b) determining whether the ingested plant DNA corresponds with DNA of the plants from which the lanternfly was collected; and, (c) investigating the spectrum of ingested plants. We utilized gut contents of third and fourth instar nymphs that were collected from multiple plants; we isolated ingested plant DNA and identified consumed plants. We demonstrated that (a) up to 534 bp of the rbcL gene from ingested plants can be detected in L. delicatula guts, (b) ingested plants in ~93% of the nymphs did not correspond with the plants from which the nymphs were collected, and (c) both introduced and native plants, as well as woody and non-woody plants, were ingested. This information will aid effective the monitoring and management of the lanternfly, as well as predict the lanternfly host plants with range expansion.

Prototype 3D-Printed Traps Capture Bactericera cockerelli (Šulc) (Hemiptera: Triozidae) Directly into Preservative for Improved Detection of “Candidatus Liberibacter solanacearum”

Potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae), is a key pest of potato (Solanum tuberosum L.) and other solanaceous crops (Solanales: Solanaceae) as a vector of “Candidatus Liberibacter solanacearum” (Lso), the pathogen associated with zebra chip disease of potato. Potato psyllid populations typically are monitored using sticky card traps, and psyllids collected from sticky traps often are subjected to polymerase chain reaction (PCR) to monitor the incidence of Lso within psyllid populations. Psyllids collected from sticky traps are often mangled, desiccated, and coated with sticky residue, which may interfere with detection of Lso by PCR. A recently developed prototype 3-dimensional-printed trap that captures insects directly into a preservative (70% ethanol) was previously tested for monitoring psyllid populations. The capture of psyllids directly into a preservative may reduce degradation of DNA or protect specimens from PCR-inhibiting contaminants, thus improving the detection of Lso by PCR. Our goal was to compare the detectability of Lso in psyllids captured into preservative (prototype trap) to that in psyllids removed from sticky card traps. Overall, detection rates were higher in psyllids from the prototype trap than from sticky card traps. This improvement in Lso detection appeared to be partly due to the specimens yielding more DNA of higher quality. Results of this study demonstrate that compared with sticky card traps, a trap that captures psyllids directly into a preservative provides higher quality specimens for collection of molecular data, including pathogen diagnosis, population genetics, and molecular gut content analysis.

High-throughput sequencing for community analysis: the promise of DNA barcoding to uncover diversity, relatedness, abundances and interactions in spider communities

Large-scale studies on community ecology are highly desirable but often difficult to accomplish due to the considerable investment of time, labor and, money required to characterize richness, abundance, relatedness, and interactions. Nonetheless, such large-scale perspectives are necessary for understanding the composition, dynamics, and resilience of biological communities. Small invertebrates play a central role in ecosystems, occupying critical positions in the food web and performing a broad variety of ecological functions. However, it has been particularly difficult to adequately characterize communities of these animals because of their exceptionally high diversity and abundance. Spiders in particular fulfill key roles as both predator and prey in terrestrial food webs and are hence an important focus of ecological studies. In recent years, large-scale community analyses have benefitted tremendously from advances in DNA barcoding technology. High-throughput sequencing (HTS), particularly DNA metabarcoding, enables community-wide analyses of diversity and interactions at unprecedented scales and at a fraction of the cost that was previously possible. Here, we review the current state of the application of these technologies to the analysis of spider communities. We discuss amplicon-based DNA barcoding and metabarcoding for the analysis of community diversity and molecular gut content analysis for assessing predator-prey relationships. We also highlight applications of the third generation sequencing technology for long read and portable DNA barcoding. We then address the development of theoretical frameworks for community-level studies, and finally highlight critical gaps and future directions for DNA analysis of spider communities.

DNA barcoding of fogged caterpillars in Peru: A novel approach for unveiling host-plant relationships of tropical moths (Insecta, Lepidoptera).

The present study aimed to perform molecular identification of lepidopteran larvae from canopy fogging including gut-content analyses. A total of 130 lepidopteran larvae were selected from 37 fogging samples at the Panguana station, district Yuyapichis, province Puerto Inca, department Huánuco, Peru. Target trees were pre-identified and subsequently submitted to molecular confirmation of identity with three markers (rbcL, psbA and trnL-F). The COI gene of 119 lepidopteran larvae was successfully sequenced and found to belong to 92 species: Comparison of DNA barcodes with the reference database of adult moths resulted in 65 (55%) matches at species level, 32 (27%) at genus level, 19 (16%) at subfamily or family level, three just to order level. Three larvae could not be assigned to a family. For these larvae the fogged target tree now suggests a potential host-plant relationship. Molecular gut content analysis, based on High-Throughput-Sequencing was successfully tested for ten larvae corroborating feeding on the target plant in some cases but elucidating several other cases of potential ‘alternative feeding’. We propose a larger-scale approach using this rapid and efficient method including molecular gut-content analyses for comprehensively testing the ratio of ‘alternative feeders’ and pitfalls caused by collateral fogging of larvae from neighboring trees.

Predator richness predicts pest suppression within organic and conventional summer squash (Cucurbita pepo L. Cucurbitales: Cucurbitaceae)

The biodiversity-ecosystem function (BEF) hypothesis predicts that increased richness within a trophic level supports greater resource capture. However, higher predator richness commonly found within organic compared to conventional agroecosystems does not always result in enhanced pest suppression. The striped cucumber beetle, Acalymma vittatum (Coleoptera: Chrysomelidae), causes damage via direct feeding and pathogen transmission to crops in the family Cucurbitaceae. The aims of this study were to: 1) identify the predators that contribute to A. vittatum suppression using molecular gut content analysis, 2) determine if the richness of predators testing positive for A. vittatum DNA was negatively correlated with prey abundance, and 3) examine how organic versus conventional cucurbit production influenced these relationships. Using a species-specific primer for A. vittatum, we found that a diverse community of predators feed on this pest, including Carabidae, Coccinellidae, Formicidae, Henicopidae, Opiliones, Lycosidae, and Staphylinidae. The richness of predators testing positive for A. vittatum DNA within a cucurbit field was negatively correlated with pest abundance, supporting the BEF hypothesis. We found no effect of farm management on the proportion or richness of predators testing positive for pest DNA, despite a 43.4% greater pitfall trap catch of predatory taxa within organic fields. This illustrates that using traps to measure predator richness and abundance may not accurately predict the strength of biological control service provided by a guild of natural enemies. Application of molecular gut content analysis proves a useful tool in advancing both the theory and practice of conservation biological control.

Tracking mite trophic interactions by multiplex PCR.

A thorough knowledge of trophic webs in agroecosystems is essential to achieve successful biological pest control. Phytoseiid mites are the most efficient natural enemies of tetranychid mites, which include several important pests worldwide. Nevertheless, phytoseiids may feed on other food sources including other microarthropods, plants and even other phytoseiids (intraguild predation), which can interfere with biological control services. Molecular gut content analysis is a valuable tool for characterizing trophic interactions, mainly when working on microarthropods such as mites. We have designed new primers for Phytoseiidae, Tetranychidae and Thysanoptera identification and they have been multiplexed in a polymerase chain reaction (PCR) together with universal plant primers. Additionally, we have estimated prey DNA detectability success over time (DS50 ) considering the most probable events in Spanish citrus orchards: the phytoseiid Euseius stipulatus as a predator, the phytoseiid Phytoseiulus persimilis as intraguild prey, and the thrips Frankliniella occidentalis and Anaphothrips obscurus as alternative prey to Tetranychus urticae. The designed multiplex PCR allows the identification of phytoseiids (both predator and intraguild prey) and detects alternative food sources mentioned above in the gut of the phytoseiid predator. DS50 for E. stipulatus as the predator were 1.3, 2.3 and 18.7h post feeding for F. occidentalis, A. obscurus and P. persimilis as prey, respectively. Tracking of the trophic relationships within the citrus acarofauna, and the unveiling of the role of alternative food sources will pave the way for enhancing T. urticae biological control. This multiplex PCR approach could be applicable for these purposes in similar agroecosystems. © 2019 Society of Chemical Industry.

Strip intercropping peanut with maize for peanut aphid biological control and yield enhancement

Increasing crop biodiversity, such as by strip intercropping, is recognized as an effective biological control measure. However, few studies have focused on the process of strip intercropping to increase natural enemy abundance, reduce pests and subsequently reduce crop damage. In the context of organic peanut (Arachis hypogaea L.) production, maize (Zea mays L.) intercropping with peanut was proposed to provide habitat for predators that suppress peanut aphid to enhance pest control in peanut. To test this hypothesis, we compared predator communities across monoculture and intercropping systems, investigated shifts of predators in response to strip intercropping systems, and evaluated their prey consumption via PCR-based gut content analysis under realistic field conditions. Last, we assessed the biological control of peanut/maize strip intercropping in peanut production. Our results demonstrated that intercropping significantly increased ladybeetle density and significantly reduced the number of peanut aphids. In the peanut/maize strip intercropping plots, peanut aphid density was significantly related to ladybeetle density. Moreover, in the intercropping plots, more than 90% of the predators prefer to inhabit on maize, and less than 10% of the predators inhabit on peanut. Further molecular gut-content analysis revealed that the ladybeetles inhabited on maize exhibited significantly higher predation on peanut aphids in the intercropping system. Visualization of the food chains indicated that peanut aphid population in intercropping system was effectively suppressed by predator abundances in the early season. In the yield experiments, compared with the monoculture systems, the strip intercropping system presented significantly higher peanut production. Linear regression analysis revealed that peanut aphid significantly reduced the pod maturity index and peanut yield. Our results indicated that peanut/maize strip intercropping could enhance the predator number, suppress pest and reduce peanut loss. This research incorporating field studies and molecular tools demonstrates the successful conservation and biological control of peanut aphids.

MEDITERATRI project - assessing the trophic ecology of predatory arthropods in Mediterranean agriculture via DNA metabarcoding diet analyses

A type of management and the use of pesticides in arable land may negatively affect a range of soil biota and thus their food webs important for ecosystem functioning. By analysing trophic interactions we could reveal the extent of potential benefits that certain organisms can provide in biocontrol and maintaining healthy ecosystems. To evaluate the role of predatory arthropods within olive orchards and vineyards under Integrated Pest Management (IPM) and Ecological Pest Management (EPM) we collected carabid beetles together with other dominant predatory arthropods in the field (e.g. ladybugs, antlions, spiders, centipedes) and subdued the individuals to molecular gut content analyses using NGS. DNA metabarcoding diet analysis approach allowed detecting a wide variety of taxa from gut contents of the predators. In addition, using ICP-MS and LC-MS/MS we quantified Cu, pesticides and its residues in soil and animals representing different trophic guilds. Since concentrations of some toxic compounds detected in carabids body were negatively correlated with those in the soil, we aim to identify a potential vector for possible transfer of toxicants to general predators via predation. The results contribute to the risk assessment of proliferation of detected chemical compounds including copper in the ecosystem and to the knowledge on the overall field sustainability of predatory invertebrates to maximize their role in pest control. The study was conducted under the project activity of HRZZ – Mediteratri.

Phytoseiid mites prey effectively on thrips eggs: Evidence from predation trials and molecular analyses

It is generally assumed that predation by phytoseiid mites (Acarina: Phytoseiidae) on thrips is mainly limited to the first and, to a lesser extent, the second thrips instars. Thrips eggs are imbedded in plant tissue and are supposed to be out of reach of most predators. Using a dual approach combining feeding trials with molecular gut content analysis, we confirmed that eggs of the western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), can be vulnerable to attack by a subset of phytoseiid species. Of the five species investigated, the generalist predators Amblyseius largoensis and Amblyseius swirskii were shown to most readily feed on thrips eggs, followed by Neoseiulus californicus, which is classified as a selective predator of tetranychid mites. Neoseiulus longispinosus and Proprioseiopsis lenis did not or very rarely consume thrips eggs. As substantial reductions of hatching (up to 30%) were observed, predation on eggs should not be ignored when assessing the efficacy of phytoseiids as biological control agents against thrips.

Spider webs, stable isotopes and molecular gut content analysis: Multiple lines of evidence support trophic niche differentiation in a community of Hawaiian spiders

Abstract Adaptive radiations are typically characterized by niche partitioning among their constituent species. Trophic niche partitioning is particularly important in predatory animals, which rely on limited food resources for survival. We test for trophic niche partitioning in an adaptive radiation of Hawaiian Tetragnatha spiders, which have diversified in situ on the Hawaiian Islands. We focus on a community of nine species belonging to two different clades, one web‐building and the other actively hunting, which co‐occur in wet forest on East Maui. We hypothesize that trophic niches differ significantly both: (a) among species within a clade, indicating food resource partitioning, and (b) between the two clades, corresponding to their differences in foraging strategy. To assess niches of the spider species, we measure: (a) web architecture, the structure of the hunting tool, and (b) site choice, the physical placement of the web in the habitat. We then test whether differences in these parameters translate into meaningful differences in trophic niche by measuring (c) stable isotope signatures of carbon and nitrogen in the spiders’ tissues, and (d) gut content of spiders based on metabarcoding data. We find significant interspecific differences in web architecture and site choice. Importantly, these differences are reflected in stable isotope signatures among the five web‐building species, as well as significant isotopic differences between web‐builders and active hunters. Gut content data also show interspecific and inter‐clade differences. Pairwise overlaps of web architecture between species are positively correlated with overlaps of isotopic signature. Our results reveal trophic niche partitioning among species within each clade, as well as between the web‐building and actively hunting clades. Based on the correlation between web architecture and stable isotopes, it appears that the isotopic signatures of spiders’ tissues are influenced by architectural differences among their webs. Our findings indicate an important link between web structure, microhabitat preference and diet in the Hawaiian Tetragnatha. A free Plain Language Summary can be found within the Supporting Information of this article.

Multiplex PCR targeting lineage‐specific SNPs: A highly efficient and simple approach to block out predator sequences in molecular gut content analysis

Abstract Food webs form the basis of biological communities, though empirical research has been hindered by difficulties in quantifying interactions. Metabarcoding from predator gut content extractions with universal primers promises to provide simple and rapid insights into food web interactions. However, the highly overabundant predator DNA often completely out‐competes that of the digested prey DNA during PCR, impeding the ability to assess the abundance and diversity of prey items. Focusing on the issue of overabundance of predator DNA amplified by a commonly used COI primer pair, we use predator lineage‐specific SNPs at the 3’‐end of PCR primers to selectively block out predators from amplification. While this approach largely prevents predator amplification, it retains high taxonomic versatility for prey lineages. We introduce a novel multilocus assay, targeting four nuclear and mitochondrial rDNA markers, and test our approach in a diverse set of spiders from 12 families. We estimate the recovered prey DNA proportions and compare the taxonomic composition of prey communities between markers. Using a feeding experiment, we also explore recovery of prey DNA over time. While commonly used COI primers yield low and very unpredictable amounts of prey DNA, our assay allows for a considerable and consistent prey enrichment across all tested species. The recovered prey's taxonomic composition is comparable between markers and supports results acquired by COI. The new marker set can be amplified in a simple multiplex PCR, considerably reducing the necessary workload. Our multilocus approach allows the generation of an unprecedented amount of prey data at low cost and effort. Lineage‐specific PCR is taxonomically versatile and could readily be adapted to any prey–predator interaction, opening up the opportunity for community‐wide studies on food web interactions.

No guts, no glory: Gut content metabarcoding unveils the diet of a flower‐associated coastal sage scrub predator

AbstractInvertebrate generalist predators are ubiquitous and play a major role in food‐web dynamics. Molecular gut content analysis (MGCA) has become a popular means to assess prey ranges and specificity of cryptic arthropods in the absence of direct observation. While this approach has been widely used to study predation on economically important taxa (i.e., pests) in agroecosystems, it is less frequently used to study the broader trophic interactions involving generalist predators in natural communities such as the diverse and threatened coastal sage scrub communities of Southern California. Here, we employ DNA metabarcoding‐based MGCA and survey the taxonomically and ecologically diverse prey range of Phymata pacifica Evans, a generalist flower‐associated ambush bug (Hemiptera: Reduviidae). We detected predation on a wide array of taxa including beneficial pollinators, potential pests, and other predatory arthropods. The success of this study demonstrates the utility of MGCA in natural ecosystems and can serve as a model for future diet investigations into other cryptic and underrepresented communities.

Host and Non-host 'Whistle Stops' for Psyllids: Molecular Gut Content Analysis by High-Throughput Sequencing Reveals Landscape-Level Movements of Psylloidea (Hemiptera).

Psyllids (Hemiptera: Psylloidea) are phloem-feeding insects that tend to be highly specific in their host plants. Some species are well-known agricultural pests, often as vectors of plant pathogens. Many pest psyllids colonize agricultural fields from non-crop reproductive hosts or from non-host transitory and winter shelter plants. Uncertainty about which non-crop species serve as sources of psyllids hinders efforts to predict which fields or orchards are at greater risk of being colonized by psyllids. High-throughput sequencing of trnL, trnF, and ITS was used to examine the dietary histories of three pest and two non-pest psyllid species encompassing a diversity of lifecycles: Cacopsylla pyricola (Förster) (Psyllidae), Bactericera cockerelli (Šulc) (Triozidae), Diaphorina citri Kuwayama (Liviidae), Aphalara loca Caldwell (Aphalaridae), and a Cacopsylla species complex associated with Salix (Malphighiales: Salicaceae). Results revealed an unexpectedly high level of feeding on non-host species by all five psyllid species. The identification of the dietary history of the psyllids allowed us to infer their landscape-scale movements prior to capture. Our study demonstrates a novel use for gut content analysis-to provide insight into landscape-scale movements of psyllids-thus providing a means to pinpoint the non-crop sources of pest psyllids colonizing agricultural crops. We observed previously unknown psyllid behaviors during our efforts to develop this method and discuss new research directions for the study of psyllid ecology.

Assessing changes in arthropod predator-prey interactions through DNA-based gut content analysis-variable environment, stable diet.

Analysing the structure and dynamics of biotic interaction networks and the processes shaping them is currently one of the key fields in ecology. In this paper, we develop a novel approach to gut content analysis, thereby deriving a new perspective on community interactions and their responses to environment. For this, we use an elevational gradient in the High Arctic, asking how the environment and species traits interact in shaping predator-prey interactions involving the wolf spider Pardosa glacialis. To characterize the community of potential prey available to this predator, we used pitfall trapping and vacuum sampling. To characterize the prey actually consumed, we applied molecular gut content analysis. Using joint species distribution models, we found elevation and vegetation mass to explain the most variance in the composition of the prey community locally available. However, such environmental variables had only a small effect on the prey community found in the spider's gut. These observations indicate that Pardosa exerts selective feeding on particular taxa irrespective of environmental constraints. By directly modelling the probability of predation based on gut content data, we found that neither trait matching in terms of predator and prey body size nor phylogenetic or environmental constraints modified interaction probability. Our results indicate that taxonomic identity may be more important for predator-prey interactions than environmental constraints or prey traits. The impact of environmental change on predator-prey interactions thus appears to be indirect and mediated by its imprint on the community of available prey.

Comparative analysis of diet in syntopic geophilomorph species (Chilopoda, Geophilomorpha) using a DNA-based approach

Trophic niche partitioning between potentially competing species within the same coenosis has been little explored for most of the major groups of arthropod soil predators, among which are the geophilomorph centipedes. We performed a comparative study in nature on the diet of three species of Geophilomorpha living in the same site in Southern Europe. Through PCR-based molecular gut content analysis, we estimated trophic niche width and overlap with respect to three common prey groups: lumbricids, collembolans and dipteran larvae. Results show that apparently similar geophilomorph species differ significantly in prey spectrum, with quite different niche widths. Estimates of predator diet overlap gave moderate values, non-significantly different from null expectations. Within-species diet composition does not vary significantly with sex. This work, while providing the first evidence of trophic niche partitioning among coexisting geophilomorph species, contributes to recent progresses in the understanding of intra-guild interactions between predators in the soil food webs.

Seasonally varying marine influences on the coastal ecosystem detected through molecular gut analysis.

Terrestrial predators on marine shores benefit from the inflow of organisms and matter from the marine ecosystem, often causing very high predator densities and indirectly affecting the abundance of other prey species on shores. This indirect effect may be particularly strong if predators shift diets between seasons. We therefore quantified the seasonal variation in diet of two wolf spider species that dominate the shoreline predator community, using molecular gut content analyses with general primers to detect the full prey range. Across the season, spider diets changed, with predominantly terrestrial prey from May until July and predominantly marine prey (mainly chironomids) from August until October. This pattern coincided with a change in the spider age and size structure, and prey abundance data and resource selection analyses suggest that the higher consumption of chironomids during autumn is due to an ontogenetic diet shift rather than to variation in prey abundance. The analyses suggested that small dipterans with a weak flight capacity, such as Chironomidae, Sphaeroceridae, Scatopsidae and Ephydridae, were overrepresented in the gut of small juvenile spiders during autumn, whereas larger, more robust prey, such as Lepidoptera, Anthomyidae and Dolichopodidae, were overrepresented in the diet of adult spiders during spring. The effect of the inflow may be that the survival and growth of juvenile spiders is higher in areas with high chironomid abundances, leading to higher densities of adult spiders and higher predation rates on the terrestrial prey next spring.

Molecular gut content analysis of different spider body parts.

Molecular gut-content analysis has revolutionized the study of food webs and feeding interactions, allowing the detection of prey DNA within the gut of many organisms. However, successful prey detection is a challenging procedure in which many factors affect every step, starting from the DNA extraction process. Spiders are liquid feeders with branched gut diverticula extending into their legs and throughout the prosoma, thus digestion takes places in different parts of the body and simple gut dissection is not possible. In this study, we investigated differences in prey detectability in DNA extracts from different parts of the spider´s body: legs, prosoma and opisthosoma, using prey-specific PCR and metabarcoding approaches. We performed feeding trials with the woodlouse hunter spider Dysdera verneaui Simon, 1883 (Dysderidae) to estimate the time at which prey DNA is detectable within the predator after feeding. Although we found that all parts of the spider body are suitable for gut-content analysis when using prey-specific PCR approach, results based on metabarcoding suggested the opisthosoma is optimal for detection of predation in spiders because it contained the highest concentration of prey DNA for longer post feeding periods. Other spiders may show different results compared to D. verneaui, but given similarities in the physiology and digestion in different families, it is reasonable to assume this to be common across species and this approach having broad utility across spiders.

High Redundancy as well as Complementary Prey Choice Characterize Generalist Predator Food Webs in Agroecosystems

Food web structure influences ecosystem functioning and the strength and stability of associated ecosystem services. With their broad diet, generalist predators represent key nodes in the structure of many food webs and they contribute substantially to ecosystem services such as biological pest control. However, until recently it has been difficult to empirically assess food web structure with generalist predators. We utilized DNA-based molecular gut-content analyses to assess the prey use of a set of generalist invertebrate predator species common in temperate agricultural fields. We investigated the degree of specialization of predator-prey food webs at two key stages of the cropping season and analysed the link temperature of different trophic links, to identify non-random predation. We found a low level of specialization in our food webs, and identified warm and cool links which may result from active prey choice or avoidance. We also found a within-season variation in interaction strength between predators and aphid pests which differed among predator species. Our results show a high time-specific functional redundancy of the predator community, but also suggest temporally complementary prey choice due to within-season succession of some predator species.