Predator Gut Research Articles

Diversified cropping strengthens herbivore regulation by providing seasonal resource continuity to predators

Abstract Agricultural practices shape arthropod communities in arable fields, consequently influencing their interactions and the resulting ecosystem services, in particular pest regulation. Predatory arthropods play a pivotal role by preying on herbivores, soil fauna, and on other predators. However, the intricate mechanisms through which agricultural practices shape the dietary preferences of predators, and regulate herbivore populations remain complex and inadequately understood. We assessed how fertilisation with organic fertiliser and extending crop rotations with perennial ley affected predation pressure across prey taxa. We mapped predator and prey trophic linkages with molecular analysis of carabid predator gut contents, and measured densities and taxonomic richness of predators, herbivores, and soil fauna in 19 cereal fields during three samplings across the growing season. We derived two food web structure metrics: prey vulnerability that is the average number of predators feeding on a selected prey, and predator trophic redundancy, that is dietary overlap. Prey vulnerability was compared among soil fauna, herbivores, and other predator species (that is interspecific intraguild predation) over the growing season, and across treatments. The mechanistic underpinnings of observed shifts in vulnerability of herbivorous prey at different crop stages were identified using information criteria to select among candidate variables related to the richness, density and interaction structure of the different guilds during both the current, and the previous crop stages. Agricultural diversification via organic fertilisation combined with perennial ley in the crop rotation decreased the vulnerability of both intraguild prey and soil fauna prey, and stabilised herbivore vulnerability. Mechanistically, the vulnerability of herbivorous prey at crop ripening emerges from the combination of predator richness and trophic redundancy during this sampling round, rather than from carryover effects from previous crop stages. Synthesis and applications: Our results suggest that locally provided resource continuity through diversified cropping practices bolster biological pest regulation, thus underline the importance of lesser disturbance in arable ecosystems for the provision of ecosystem services. Enhanced predator species richness together with availability of alternative prey through the season underpins this enhanced pest regulation.

Prey ration, temperature, and predator species influence digestion rates of prey DNA inferred from qPCR and metabarcoding.

Diet analysis is a vital tool for understanding trophic interactions and is frequently used to inform conservation and management. Molecular approaches can identify diet items that are impossible to distinguish using more traditional visual-based methods. Yet, our understanding of how different variables, such as predator species or prey ration size, influence molecular diet analysis is still incomplete. Here, we conducted a large feeding trial to assess the impact that ration size, predator species, and temperature had on digestion rates estimated with visual identification, qPCR, and metabarcoding. Our trial was conducted by feeding two rations of Chinook salmon (Oncorhynchus tshawytscha) to two piscivorous fish species (largemouth bass [Micropterus salmoides] and channel catfish [Ictalurus punctatus]) held at two different temperatures (15.5 and 18.5°C) and sacrificed at regular intervals up to 120 h from the time of ingestion to quantify the prey contents remaining in the digestive tract. We found that ration size, temperature, and predator species all influenced digestion rate, with some indication that ration size had the largest influence. DNA-based analyses were able to identify salmon smolt prey in predator gut samples for much longer than visual analysis (~12 h for visual analysis vs. ~72 h for molecular analyses). Our study provides evidence that modelling the persistence of prey DNA in predator guts for molecular diet analyses may be feasible using a small set of controlling variables for many fish systems.

From prey to predators: Evidence of microplastic trophic transfer in tuna and large pelagic species in the southwestern Tropical Atlantic

Plastic pollution is present in most marine environments; however, contamination in pelagic predators, including species of economic interest, is still poorly understood. This study aims to access the macro- and microplastic contamination in tuna and large pelagic species and verify whether a trophic transfer occurs from prey to tunas captured by two fleets in the Southwestern Tropical Atlantic (SWTA). We combined different methodological approaches to analyse the intake of macro- and microplastics. In addition to examining the plastics in the fish’ stomachs, we investigated the contamination in the prey retrieved from the guts of predators. A low frequency of occurrence (3%) of macroplastic was detected in the tuna and large pelagic species; conversely, we observed a high frequency of microplastic in the tuna's stomachs (100%) and prey analysed (70%). We evinced the trophic transfer of microplastics by analysing the ingestion rate of particles in prey retrieved from the tuna stomachs. In the 34 analysed prey, we detected 355 microplastic particles. The most contaminated prey were cephalopods and fishes of the Bramidae family. The most frequent microplastic shapes in both prey and tuna stomachs were foams, pellets and fibres (<1 mm). A variety of polymers were identified; the most frequent were styrene-butadiene rubber (SBR), polyamide (PA), polyethylene terephthalate (PET) and polyethylene (PE). Our findings enhance scientific knowledge of how the ecological behaviour of marine species can affect microplastic intake.

How many predator guts are required to predict trophic interactions?

1)A large obstacle in food web ecology is the time and effort required to adequately describe the structure of a food web using individual predator guts. Food web models such as the allometric diet breadth model (ADBM) can be used to circumvent this problem by predicting the interactions based on easily measured characteristics, such as the size of organisms. However, diet data such as that which comes from analysis of predator guts is still required to parameterise these food web models, and collecting and analysing these data from the field is an expensive and time-consuming task. Therefore, it is important to know how many predator guts are required to parameterise food web models to obtain food web structures with high accuracy and precision.2)Here, we explore seven exceptionally well-characterised food webs and determine the minimum number of predator guts needed to accurately predict their structure using the ADBM. We use Bayesian computation to parameterise the ADBM, and true skill statistics to measure the goodness of fit, and do so while varying the number of predator guts used in the parameterisation to test the effect of sampling effort.3)We found that relatively few, and many fewer than were actually collected, predator guts can be used to parameterise the ADBM. The lowest number of predator guts was 27% of the number of available predator guts. The number of predator guts required to accurately characterise food webs increases by ∼ 7 ±2.2 guts for 10 units increase in the number of trophic links and ∼ 9 ±4.7 guts for a unit increase in the number of species.4)These results suggest that one need not collect and analyse such a large quantity of predator guts in order to adequately predict the structure of a food web, thereby reducing sampling effort considerably, while having little effect on precision or accuracy of predictions.

Metabarcoding versus mapping unassembled shotgun reads for identification of prey consumed by arthropod epigeal predators.

BackgroundA central challenge of DNA gut content analysis is to identify prey in a highly degraded DNA community. In this study, we evaluated prey detection using metabarcoding and a method of mapping unassembled shotgun reads (Lazaro).ResultsIn a mock prey community, metabarcoding did not detect any prey, probably owing to primer choice and/or preferential predator DNA amplification, while Lazaro detected prey with accuracy 43–71%. Gut content analysis of field-collected arthropod epigeal predators (3 ants, 1 dermapteran, and 1 carabid) from agricultural habitats in Brazil (27 samples, 46–273 individuals per sample) revealed that 64% of the prey species detections by either method were not confirmed by melting curve analysis and 87% of the true prey were detected in common. We hypothesized that Lazaro would detect fewer true- and false-positive and more false-negative prey with greater taxonomic resolution than metabarcoding but found that the methods were similar in sensitivity, specificity, false discovery rate, false omission rate, and accuracy. There was a positive correlation between the relative prey DNA concentration in the samples and the number of prey reads detected by Lazaro, while this was inconsistent for metabarcoding.ConclusionsMetabarcoding and Lazaro had similar, but partially complementary, detection of prey in arthropod predator guts. However, while Lazaro was almost 2× more expensive, the number of reads was related to the amount of prey DNA, suggesting that Lazaro may provide quantitative prey information while metabarcoding did not.

Whose Kids Did You Eat? Genetic Identification of Species and Parents of Larval Lampreys in Fish Predator Guts

AbstractThe Pacific Lamprey Entosphenus tridentatus is an important species both ecologically and culturally, but their population numbers and range have declined severely in the past several decades in the Columbia Basin. In freshwater ecosystems, larval lampreys are candidate prey species for many fish predators, but little is known regarding the magnitude of predation they currently experience. Predation on larval Pacific Lampreys may be substantially underestimated by morphological gut content analysis because their soft bodies are quickly digested and leave no hard evidence, such as bones and scales. We conducted an experimental predation study and analyzed larval Pacific Lampreys in the gut contents of predators’ digestive tracts via both morphological and molecular methods. Whereas most consumed larval lampreys (67–100%) were morphologically unidentifiable within two nights, genetic species identification rates using four single nucleotide polymorphisms from stomachs were high (83%). The single nucleotide polymorphisms optimized for parentage in Pacific Lamprey also successfully identified the parents of four out of five Pacific Lampreys with complete genotypes. When a genetic baseline of candidate parents is available, this molecular technique using parentage‐based tagging offers a novel method for determining precise characteristics of predation behavior in field studies, including the ages and natal origins of larvae being consumed.

Predation on Drosophila suzukii within Hedges in the Agricultural Landscape.

Simple SummaryDrosophila suzukii is an invasive species that feeds and reproduces on various cultivated and wild fruits and moves between agricultural and semi-natural habitats, such as hedges and forest patches. These semi-natural habitats are known to harbor a diverse community of natural enemies of pests. When we exposed D. suzukii pupae in dry and humid hedges, we found that on average 44% of them were predated within four days. The most common predators in the hedges were earwigs, spiders, and ants. Using a molecular assay that detects the DNA of D. suzukii in the gut of predators, we could show that 3.4% of the sampled earwigs, 1.8% of the spiders, and one predatory bug had fed on D. suzukii. This small proportion may be due to methodological constraints. However, the overall predation rate helps to reduce D. suzukii populations, in particular in hedges that are scarce of host fruits.The invasive Drosophila suzukii feeds and reproduces on various cultivated and wild fruits and moves between agricultural and semi-natural habitats. Hedges in agricultural landscapes play a vital role in the population development of D. suzukii, but also harbor a diverse community of natural enemies. We investigated predation by repeatedly exposing cohorts of D. suzukii pupae between June and October in dry and humid hedges at five different locations in Switzerland. We sampled predator communities and analyzed their gut content for the presence of D. suzukii DNA based on the COI marker. On average, 44% of the exposed pupae were predated. Predation was higher in dry than humid hedges, but did not differ significantly between pupae exposed on the ground or on branches and among sampling periods. Earwigs, spiders, and ants were the dominant predators. Predator communities did not vary significantly between hedge types or sampling periods. DNA of D. suzukii was detected in 3.4% of the earwigs, 1.8% of the spiders, and in one predatory bug (1.6%). While the molecular gut content analysis detected only a small proportion of predators that had fed on D. suzukii, overall predation seemed sufficient to reduce D. suzukii populations, in particular in hedges that provide few host fruit resources.

Compared with conventional PCR assay, qPCR assay greatly improves the detection efficiency of predation.

Studies of predation can contribute greatly to understanding predator–prey relationships and can also provide integral knowledge concerning food webs and multi‐trophic level interactions. Both conventional polymerase chain reaction (cPCR) and quantitative PCR (qPCR) have been employed to detect predation in the field because of their sensitivity and reproducibility. However, to date, few studies have been used to comprehensively demonstrate which method is more sensitive and reproducible in studies of predation. We used a Drosophila melanogaster‐specific DNA fragment (99 bp) to construct a tenfold gradient dilution of standards. Additionally, we obtained DNA samples from Pardosa pseudoannulata individuals that fed on D. melanogaster at various time since feeding. Finally, we compared the sensitivity and reproducibility between cPCR and qPCR assays for detecting DNA samples from feeding trials and standards. The results showed that the cPCR and qPCR assays could detect as few as 1.62 × 103 and 1.62 × 101 copies of the target DNA fragment, respectively. The cPCR assay could detect as few as 48 hr post‐feeding of the target DNA fragment. But the qPCR assay showed that all spiders were positive after consuming prey at various time intervals (0, 24, 48, 72, and 96 hr). A smaller proportion of the technical replicates were positive using cPCR, and some bands on the agarose gel were absent or gray, while some were white and bright for the same DNA samples after amplification by cPCR. By contrast, a larger proportion of the technical replicates were positive using qPCR and the coefficients of variation of the Ct value for the three technical replicates of each DNA sample were less than 5%. These data showed that qPCR was more sensitive and highly reproducible in detecting such degraded DNA from predator's gut. The present study provides an example of the use of cPCR and qPCR to detect the target DNA fragment of prey remains in predator's gut.

A procedure for pinpointing cannibalism, intraguild predation, and life stage-specific feeding events

A predator gut analysis technique is described that can simultaneously pinpoint predation events which are life stage-specific, intraspecies-specific (cannibalism) and interspecies-specific (intraguild). The third and fifth larval life stages of green lacewing, Chrysoperla carnea Stephens s.l. (Neuroptera: Chrysopidae), were marked with rabbit IgG and chicken IgY, respectively. The uniquely marked lacewing life stages were then introduced into caged arenas (n = 59 caged experimental units) containing a cotton plant and an assemblage of generalist predators. The predators released into each arena were recaptured after 6 h and their gut contents were examined for the presence of rabbit IgG- and chicken IgY-marked lacewing remnants by an anti-rabbit and anti-chicken enzyme-linked immunosorbent assay (ELISA), respectively. The predator gut ELISAs detected one cannibalism event and 14 and 8 intraguild predation (IGP) events on third and fifth instar lacewings, respectively. This proof-of-concept study shows that this universal prey immunomarking technique (UFIT), when combined with field cage methods, can be useful for pinpointing cannibalism and life stage-specific predation events.

Consuming alternative prey does not influence the DNA detectability half-life of pest prey in spider gut contents.

BackgroundKey natural enemy-pest interactions can be mapped in agricultural food webs by analysing predator gut content for the presence of a focal pest species. For this, PCR-based approaches are the most widely used methods providing the incidence of consumption of a focal pest in field sampled predators. To interpret such data the rate of prey DNA decay in the predators’ gut, described by DNA detectability half-life (t1/2), is needed. DNA decay may depend on the presence of alternative prey in the gut of generalist predators, but this effect has not been investigated in one of the major predatory arthropod groups, spiders.MethodsIn a laboratory feeding experiment, we determined t1/2 of the key cereal pest virus vector leafhopper Psammotettix alienus in the digestive tracts of its natural enemy, the spider Tibellus oblongus. We followed the fate of prey DNA in spiders which received only the focal prey as food, or as an alternative prey treatment they also received a meal of fruit flies after leafhopper consumption. After these feeding treatments, spiders were starved for variable time intervals prior to testing for leafhopper DNA in order to establish t1/2.ResultsWe created a PCR protocol that detects P. alienus DNA in its spider predator. The protocol was further calibrated to the digestion speed of the spider by establishing DNA decay rate. Detectability limit was reached at 14 days, where c. 10% of the animals tested positive. The calculated t1/2 = 5 days value of P. alienus DNA did not differ statistically between the treatment groups which received only the leafhopper prey or which also received fruit fly. The PCR protocol was validated in a field with known P. alienus infestation. In this applicability trial, we showed that 12.5% of field collected spiders were positive for the leafhopper DNA. We conclude that in our model system the presence of alternative prey did not influence the t1/2 estimate of a pest species, which makes laboratory protocols more straightforward for the calibration of future field data.

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.

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.

It’s Gut Check Time! A Universal Food Immunomarking Technique for Studying Arthropod Feeding Activities

The analysis of arthropod feeding activity is often determined by using species-specific postmortem gut content polymerase chain reaction and enzyme-linked immunosorbent assays (ELISA). Such mono-specific assays require time, resources, and technical expertise to develop for the food item (usually a pest insect species) that is the target of the investigation. A generic predator gut analysis method was described over a quarter of a century ago that does not require the development of a species-specific gut assay. This generic method remained in relative obscurity until about a decade ago. Recently, it has been used to study a wide range of arthropod feeding activities, such as carnivory, herbivory, scavenging, and other feeding interactions. For this review, I have coined this method as the universal food immunomarking technique (UFIT). The UFIT consists of tagging food items (i.e., prey, foliage, carrion, etc.) with a specific protein. In turn, the gut contents of foraging arthropods are examined for the presence of protein-marked food items by a standardized protein-specific sandwich ELISA. In this article, I give examples of the benefits of the UFIT gut assay approach over prey-specific gut assay approaches and tips on conducting a successful UFIT experiment, and provide examples of how it has been adapted to study a wide variety of arthropod feeding behaviors. My goal is to make researchers aware of another valuable tool in the gut analysis toolbox.

Patterns of selective predation change with ontogeny but not density in a marine fish.

Phenotypic variation is prevalent in the early life-history stages of many organisms and provides the basis for selective mortality on size and growth-related traits of older life stages. Densities of organisms can vary widely at important life-history transitions, raising additional questions about the interplay between selection and density-dependent processes. We evaluate density dependence in patterns of selective mortality for a temperate reef fish. Specifically, we exposed pre-settlement and post-settlement stages of the common triplefin (Forsterygion lapillum) to a natural predator and evaluated patterns of selective mortality on early life-history traits as a function of ontogenetic stage and density. We used otoliths to reconstruct the traits of fish that survived versus fish that were consumed (i.e., we recovered otoliths from the guts of predators), and we estimated selection by analysing the relationship between absolute fitness and standardised traits. Absolute fitness was negatively correlated with size and larval growth rate for pre-settlement fish (i.e., larger and faster growing individuals were more likely to be consumed by predators), and this was consistent across the range of densities evaluated. Post-settlement fish experienced no selective mortality. Additionally, absolute fitness was equal across density treatments, suggesting mortality was density-independent. Collectively, these results suggest that patterns of selection change with ontogeny, but may be stable across densities when mortality is density-independent. Shifts in selective mortality for species with distinct life-stages can mask and complicate relationships between traits and fitness, and the importance of such traits may be underappreciated for earlier life stages.

Standardization of prey immunomarking: does a positive test always indicate predation?

A prey immunomarking procedure (PIP) in combination with generic anti-rabbit and anti-chicken immunoglobulin G (IgG) enzyme-linked immunosorbent assays (ELISAs) are used frequently to study arthropod predation. This study was conducted to: (1) further standardize the PIP as a tool for predator gut analysis research, (2) investigate the most effective means for administering IgG marks to prey items, and (3) assess the possibility of the PIP yielding false positive reactions as a consequence of a predator obtaining a mark by incidental contact with, or by a failed predation attempt on, a protein-marked prey item. The pest Lygus hesperus Knight (Hemiptera: Miridae) was tagged with either an external rabbit IgG mark, an internal chicken IgG mark, or a double (external rabbit IgG and internal chicken IgG) mark treatment. Then, the variously marked prey items were fed to chewing and piercing-sucking type predators and their gut contents were examined for the presence of IgG remains. Data revealed that all three marking treatments were highly effective at tagging targeted prey. However, ELISA results showed that the prey items should only be marked internally to maximize the likelihood of detecting prey remains while minimizing the risk of obtaining false positive errors. The merits and limitations of using the generic PIP for predator gut analysis research are discussed.

Predation on Bivalves on a Sandy Beach in Soma, Japan

Predation may be an important cause of early postsettlement mortality of bivalves, but little is known of in situ predation processes on bivalves by multiple predators on sandy beaches. To address this issue, bivalve shells in the guts of demersal fishes and benthic invertebrates were counted and measured monthly from April to November 2009 in Soma, Japan. For the Sakhalin surf clams Pseudocardium sachalinense and Raeta pulchella, the frequency of occurrence and number of shells in guts of predators per transect peaked around May–June, when the length of shells in guts tended to be smaller than in later months. These two indices decreased to 0 in July for P. sachalinense and to a low level in August for R. pulchella, which was associated with increasing shell length (ShL) in guts. For the bivalve Mactra crossei, both occurrence and number of shells in guts of predators per transect increased around November in some of the predators. The largest ShL of P. sachalinense in guts tended to be similar among the predators and was 1.1–1.5 mm. The largest ShL of R. pulchella and M. crossei tended to vary among the predators, and were 5.6–17.8 mm and 1.0–7.2 mm, respectively. The spiny sand sea star Luidia quinaria and red tongue sole Cynoglossus joyneri had a high frequency of occurrence and number of shells per gut per transect. These results indicate that predation on P. sachalinense and R. pulchella was most intense in the early postsettlement period of May–June in Soma, Japan. The size of the bivalve shell may have provided protection, but was dependent upon on the predator.

Feeding ecology of early life stages of mesopelagic fishes in the equatorial and tropical Atlantic

Abstract We analysed the trophic ecology of the early ontogenetic stages of six mesopelagic fish species (Bathylagoides argyrogaster, Argyropelecus sladeni, Sternoptyx diaphana, Diaphus vanhoeffeni, Hygophum macrochir, and Myctophum affine), which have different morphologies, vertical distributions, and taxonomic affiliations. The larvae and transforming stages of the sternoptychids fed both during the day and at night. However, larvae of the other species fed during the day, as they apparently rely on light for prey capture. The transforming stages of myctophids showed a similar daylight feeding pattern to their larvae, but in D. vanhoeffeni both day and night feeding was evident, thereby indicating the progressive change toward the adult nocturnal feeding pattern. The number of prey and their maximum sizes were linked to predator gut morphology and gape size. Although the maximum prey size increased with predator development, postflexion larvae and transforming stages also preyed on small items, so that the trophic niche breath did not show evidence of specialization. In all the species, copepods dominated the larval diet, but the transforming stages were characterized by increasing diet diversity. Despite the poor development of these early stages, Chesson’s selectivity index calculated for larvae and transforming stages showed positive selection for particular prey.

Fast molecular assay to detect the rate of decay of Bactrocera oleae (Diptera: Tephritidae) DNA in Pterostichus melas (Coleoptera: Carabidae) gut contents

The molecular analysis of predation through specific DNA amplification has been utilized extensively over the last decade, and has been shown to be fast and effective. However, it is necessary to evaluate the prey detectability half-life if we are to correctly infer the relevance of particular predators to particular pests and to accurately model the effect of biocontrol. We present here the design and analysis of a set of primers to amplify olive fruit fly (Bactrocera oleae) DNA in predator gut contents, allowing fast evaluation of the digestion time. We modified the existing protocol by solubilizing the prey DNA directly from the gut, and we applied this modified protocol to demonstrate that Pterostichus melas, one of the most common carabids in olive groves in Italy, feeds on B. oleae pupae. After feeding carabids with a single pupa, traces of the pest were found to be detectable more than 20 h after ingestion. This method could also be applied to other predators to evaluate trophic interactions of the olive fruit fly. The relevance of generalist predation to the mortality of the pupal stage of B. oleae is of great economic interest since B. oleae causes serious damage during olive production, reducing the commercial value of olive oil and table olives.

A simple and cost-effective molecular method to track predation on Drosophila suzukii in the field

The vinegar fly Drosophila suzukii (Matsumura) is an invasive species that attacks ripening fruits and berries, leading to considerable losses in fruit production. So far, management mainly relies on chemical and cultural control, but additional measures such as biological control are needed. Hence, for the development of sustainable control measures of this pest it is important to identify potential natural enemies such as generalist predators that feed on D. suzukii. Here, we established a simple and cost-effective assay to specifically detect D. suzukii DNA in the guts of arthropod predators. Furthermore, we developed a general Drosophila spp. primer pair to identify predators of Drosophila species in general that might also feed on D. suzukii and to compare predation rates on D. suzukii to those of other Drosophila species. We applied the assays to field-collected predators and identified three predator taxa—earwigs, spiders and predatory bugs—that had fed on D. suzukii. The assays provide a first step towards unravelling the predator community attacking D. suzukii that should be considered as biological control agents but also as non-targets potentially affected by other measures to control this invasive pest.

Comparisons of stable isotope (C, H, N) signatures for revealing organic matter sources and trophic relationships in headwater streams

We compared the efficacy of stable carbon, hydrogen, and nitrogen isotope ratios in identifying the resources used by insect consumers in headwater streams of southern California. We also compared gut contents with consumer stable isotope ratios and mixing model estimates of resource contributions to predator diet. Stable hydrogen isotope ratios (as δ2H) of algivores were well separated from ratios for detritivores, whereas relationships between stable carbon (as δ13C) and nitrogen (as δ15N) ratios of consumers and their expected diets were weaker and more ambiguous. δ2H values of primary consumers more strongly reflected the proportions of their gut contents consisting of algae than δ13C values. Τhe proportions of algivorous prey in predator gut contents increased with mixing model estimates of algivore contributions to predator diet using δ2H but not δ13C values. Our findings support the use of hydrogen isotope ratios in food web studies of streams in southern California and their potential use in assessing the effects of anthropogenic and natural disturbance on basal resource contributions to food webs that might not otherwise be identified using carbon isotope ratios.