Identifying the predator complex of Homalodisca vitripennis (Hemiptera: Cicadellidae): a comparative study of the efficacy of an ELISA and PCR gut content assay

DNA High-Throughput Sequencing for Arthropod Gut Content Analysis to Evaluate Effectiveness and Safety of Biological Control Agents

The search for effective biological control agents without harmful non-target effects has been constrained by the use of impractical (field direct observation) or imprecise (cage experiments) methods. While advances in the DNA sequencing methods, more specifically the development of high-throughput sequencing (HTS), have been quickly incorporated in biodiversity surveys, they have been slow to be adopted to determine arthropod prey range, predation rate and food web structure, and critical information to evaluate the effectiveness and safety of a biological control agent candidate. The lack of knowledge on how HTS methods could be applied by ecological entomologists constitutes part of the problem, although the lack of expertise and the high cost of the analysis also are important limiting factors. In this review, we describe how the latest HTS methods of metabarcoding and Lazaro, a method to identify prey by mapping unassembled shotgun reads, can serve biological control research, showing both their power and limitations. We explain how they work to determine prey range and also how their data can be used to estimate predation rates and subsequently be translated into food webs of natural enemy and prey populations helping to elucidate their role in the community. We present a brief history of prey detection through molecular gut content analysis and also the attempts to develop a more precise formula to estimate predation rates, a problem that still remains. We focused on arthropods in agricultural ecosystems, but most of what is covered here can be applied to natural systems and non-arthropod biological control candidates as well.

Molecular diet analysis enables detection of diatom and cyanobacteria DNA in the gut of Macoma balthica

Detritivores are essential to nutrient cycling, but are often neglected in trophic networks, due to difficulties with determining their diet. DNA analysis of gut contents shows promise of trophic link discrimination, but many unknown factors limit its usefulness. For example, DNA can be rapidly broken down, especially by digestion processes, and DNA provides only a snapshot of the gut contents at a specific time. Few studies have been performed on the length of time that prey DNA can be detected in consumer guts, and none so far using benthic detritivores. Eutrophication, along with climate change, is altering the phytoplankton communities in aquatic ecosystems, on which benthic detritivores in aphotic soft sediments depend. Nutrient-poor cyanobacteria blooms are increasing in frequency, duration, and magnitude in many water bodies, while nutrient-rich diatom spring blooms are shrinking in duration and magnitude, creating potential changes in diet of benthic detritivores. We performed an experiment to identify the taxonomy and quantify the abundance of phytoplankton DNA fragments on bivalve gut contents, and how long these fragments can be detected after consumption in the Baltic Sea clam Macoma balthica. Two common species of phytoplankton (the cyanobacteria Nodularia spumigena or the diatom Skeletonema marinoi) were fed to M. balthica from two regions (from the northern and southern Stockholm archipelago). After removing the food source, M. balthica gut contents were sampled every 24 hours for seven days to determine the number of 23S rRNA phytoplankton DNA copies and when the phytoplankton DNA could no longer be detected by quantitative PCR. We found no differences in diatom 18S rRNA gene fragments of the clams by region, but the southern clams showed significantly more cyanobacteria 16S rRNA gene fragments in their guts than the northern clams. Interestingly, the cyanobacteria and diatom DNA fragments were still detectable by qPCR in the guts of M. balthica one week after removal from its food source. However, DNA metabarcoding of the 23S rRNA phytoplankton gene found in the clam guts showed that added food (i.e. N. spumigena and S. marinoi) did not make up a majority of the detected diet. Our results suggest that these detritivorous clams therefore do not react as quickly as previously thought to fresh organic matter inputs, with other phytoplankton than large diatoms and cyanobacteria constituting the majority of their diet. This experiment demonstrates the viability of using molecular methods to determine feeding of detritivores, but further studies investigating how prey DNA signals can change over time in benthic detritivores will be needed before this method can be widely applicable to both models of ecological functions and conservation policy.

Zelus renardii Roaming in Southern Italy

Simple Summary

The leafhopper assassin bug Zelus renardii (Hemiptera: Reduviidae) first entered Europe in 2012 and has since acclimatised. Z. renardii is now a common insect predator in agroecosystems and urban and peri-urban areas. We performed a metadata analysis of 165 years of Z. renardii literature. Moreover, we provide laboratory tests of Z. renardii predation. The latter indicates Z. renardii interplay with relevant insect targets, such as Philaenus spumarius, Neophilaenuscampestris, Bactrocera oleae, Kermes vermilio, Nidularia pulvinata, Harmonia axyridis, Apis mellifera, Aleurocanthus spiniferus, Aleurothrixus floccosus, Macrohomotoma gladiata, Drosophila suzukii, Drosophila melanogaster, Megaselia scalaris, Pseudococcidae, Miridae, and Issidae. Furthermore, predation on Aphrophoridae and other olive pests brands Z. renardii as a good mass-rearing candidate for inundative biocontrol programs of Xylella fastidiosa pauca ST53 infections and could also reduce damage caused by other olive pests. Overall, this reduviid is harmless to humans and beneficial insects.

Abstract

This study collects data from the literature and updates our Zelus renardii Kolenati, 1856 (Leafhopper Assassin Bug, LAB) prey knowledge. The literature consists of ca. 170 entries encompassing the years 1856 to 2021. This reduviid originated in the Nearctic region, but has entered and acclimatised in many Mediterranean countries. Our quantitative predation experiments—in the laboratory on caged plants plus field or environmental observations—confirm that LAB prefers a selected array of prey. Laboratory predation tests on living targets (Hemiptera, Coleoptera, Diptera, and Hymenoptera) agree with the literature. Zelus renardii prefers comparatively large, highly mobile, and readily available prey. LAB preferences on available hemipterans targets suggest that Zelus renardii is a good inundative biocontrol agent for Xylella fastidiosapauca ST53 infections. LAB also prey on other important olive pests, such as Bactrocera oleae. Therefore, Zelus renardii is a major integrated pest management (IPM) component to limit Xylella fastidiosa pandemics and other pest invasions.

A Molecular Approach for Detecting Stage-Specific Predation on Lygus hesperus (Hemiptera: Miridae)

A molecular gut analysis technique is described to identify predators of Lygus hesperus (Knight), a significant pest of many crops. The technique is unique because it can pinpoint which life stage of the pest was consumed. Sentinel egg masses designed to mimic the endophytic egg-laying behavior of L. hesperus were marked with rabbit serum, while third instar and adult L. hesperus were marked with chicken and rat sera, respectively. Then, the variously labeled L. hesperus life stages were introduced into field cages that enclosed the native arthropod population inhabiting an individual cotton plant. After a 6-h exposure period, the predator assemblage, including the introduced and native L. hesperus population, in each cage were counted and had their gut contents examined for the presence of the variously marked L. hesperus life stages by a suite of serum-specific enzyme-linked immunosorbent assays (ELISA). The whole-plant sampling scheme revealed that Geocoris punticpes (Say) and Geocoris pallens Stal (Hemiptera: Geocoridae) and members of the spider complex were the numerically dominant predator taxa in the cotton field. The gut content analyses also showed that these two taxa appeared to be the most prolific predators of the L. hesperus nymph stage. Other key findings include that Collops vittatus (Say) (Coleoptera: Melyridae) and Solenopsis xyloni McCook (Hymenoptera: Formicidae) appear to be adept at finding and feeding on the cryptic L. hesperus egg stage, and that L. hesperus, albeit at low frequencies, engaged in cannibalism. The methods described here could be adapted for studying life stage-specific feeding preferences for a wide variety of arthropod taxa.

Host plant use of a polyphagous mirid, Apolygus lucorum: Molecular evidence from migratory individuals

While the host plant use of insect herbivores is important for understanding their interactions and coevolution, field evidence of these preferences is limited for generalist species. Molecular diet analysis provides an effective option for gaining such information, but data from field-sampled individuals are often greatly affected by the local composition of their host plants. The polyphagous mirid bug Apolygus lucorum (Meyer-Dür) seasonally migrates across the Bohai Sea, and molecular analysis of migrant bugs collected on crop-free islands can be used to estimate the host plant use of A. lucorum across the large area (northern China) from where these individuals come. In this study, the host plant use of A. lucorum adults was determined by identifying plant DNA using a three-locus DNA barcode (rbcL, trnH-psbA, and ITS) in the gut of migrant individuals collected on Beihuang Island. We successfully identified the host plant families of A. lucorum adults, and the results indicated that captured bugs fed on at least 17 plant families. In addition, gut analyses revealed that 35.9% of A. lucorum individuals fed on multiple host plants but that most individuals (64.1%) fed on only one plant species. Cotton, Gossypium hirsutum L., DNA was found in 35.8% of the A. lucorum bugs examined, which was much higher than the percentage of bugs in which other host plants were found. Our work provides a new understanding of multiple host plant use by A. lucorum under natural conditions, and these findings are available for developing effective management strategies against this polyphagous pest species.

A Gut Analysis Technique for Pinpointing Egg-Specific Predation Events

A universal food immunomarking technique (UFIT) is described for postmortem gut analysis detection of predation on the egg stage of Lygus hesperus Knight (Hemiptera: Miridae). Collops vittatus Say (Coleoptera: Melyridae) and Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae) were fed a single L. hesperus egg that was marked with rabbit and chicken sera proteins. The protein-marked egg remnants were detectable in the guts of the majority of the predators by each sera-specific enzyme-linked immunosorbent assay (ELISA) for 3 to 6 h after a feeding event. A novel technique was then developed to expose protein-marked eggs to predators that simulated the L. hesperus endophytic oviposition behavior. The procedure entailed embedding L. hesperus eggs in an artificial substrate that mimicked the stem of a plant. A predator feeding choice study was then conducted in cages that contained a cotton plant and artificial stems containing endophytic (concealed) and exophytic (exposed) egg patches. The endophytic and exophytic egg treatments were marked with chicken and rabbit protein, respectively. The gut analyses revealed that higher proportions of both predator populations contained remnants of the exophytic egg treatment and L. hesperus eggs were more vulnerable to C. vittatus than H. convergens. This study shows how the UFIT can be used to pinpoint stage-specific feeding activity on two distinct egg exposure treatments (endophytic and exophytic) of the same species.

Patterns and dynamics of neutral lipid fatty acids in ants - implications for ecological studies

BACKGROUND

Trophic interactions are a fundamental aspect of ecosystem functioning, but often difficult to observe directly. Several indirect techniques, such as fatty acid analysis, were developed to assess these interactions. Fatty acid profiles may indicate dietary differences, while individual fatty acids can be used as biomarkers. Ants are among the most important terrestrial animal groups, but little is known about their lipid metabolism, and no study so far used fatty acids to study their trophic ecology. We set up a feeding experiment with high- and low-fat food to elucidate patterns and dynamics of neutral lipid fatty acids (NLFAs) assimilation in ants. We asked whether dietary fatty acids are assimilated through direct trophic transfer, how diet influences NLFA total amounts and patterns over time, and whether these assimilation processes are similar across species and life stages.

RESULTS

Ants fed with high-fat food quickly accumulated specific dietary fatty acids (C18:2n6, C18:3n3 and C18:3n6), compared to ants fed with low-fat food. Dietary fat content did not affect total body fat of workers or amounts of fatty acids extensively biosynthesized by animals (C16:0, C18:0, C18:1n9). Larval development had a strong effect on the composition and amounts of C16:0, C18:0 and C18:1n9. NLFA compositions reflected dietary differences, which became more pronounced over time. Assimilation of specific dietary NLFAs was similar regardless of species or life stage, but these factors affected dynamics of other NLFAs, composition and total fat.

CONCLUSIONS

We showed that ants accumulated certain dietary fatty acids via direct trophic transfer. Fat content of the diet had no effect on lipids stored by ants, which were able to synthesize high amounts of NLFAs from a sugar-based diet. Nevertheless, dietary NLFAs had a strong effect on metabolic dynamics and profiles. Fatty acids are a useful tool to study trophic biology of ants, and could be applied in an ecological context, although factors that affect NLFA patterns should be taken into account. Further studies should address which NLFAs can be used as biomarkers in natural ant communities, and how factors other than diet affect fatty acid dynamics and composition of species with distinct life histories.

Development and validation of a real-time PCR assay for the glassy-winged sharpshooter Homalodisca vitripennis (Hemiptera: Cicadellidae)

The glassy-winged sharpshooter (Homalodisca vitripennis) is an invasive pest organism, which is found throughout Central America and has recently invaded a few countries in the Pacific Islands. As a carrier of the highly virulent plant pathogenic bacterium Xylella fastidiosa, it is of great economic significance to horticulture and is estimated to cost Californian vineyards over US$100 million per year in control and losses. New Zealand is currently free from this pest, but its recent spread through the Pacific has raised concerns of it establishing in New Zealand, potentially as a result of introduction through human travel. We report here a real-time polymerase chain reaction assay for the rapid identification of H. vitripennis. The assay was extensively validated in silico then optimized and tested against a range of Cicadellidae species, both internationally collected and local to New Zealand. This assay was able to correctly identify H. vitripennis samples, and distinguish between H. vitripennis and close relatives, such as the smoke-tree sharpshooter (Homalodisca liturata) and will be of great benefit to New Zealand biosecurity.

Predation by generalist arthropod predators on Apolygus lucorum (Hemiptera: Miridae): molecular gut-content analysis and field-cage assessment

BACKGROUND

The mirid bug Apolygus lucorum (Meyer-Dür) is a principal pest of cotton that also causes great damage to many other crops in China. A study was conducted to assess the mortality of A. lucorum from generalist arthropod predators using both molecular methods and a field-cage trial. The species-specific primer pair for the detection of A. lucorum tissues in predators was designed according to the sequences of the cytochrome oxidase subunit I (COI) gene.

RESULTS

A total of 2096 generalist predators that consisted of ladybeetles, lacewings and spiders were collected, and A. lucorum remains were detected using the designed primers. Only 1.6% of these predators contained A. lucorum DNA, with the highest positive proportion (6.1%) for Harmonia axyridis larvae. In the field-cage experiment, the daily predation rates of second-instar A. lucorum nymphs by H. axyridis adults and larvae were 4.7 and 5.2% respectively.

CONCLUSIONS

The overall low positive proportion of generalist predators with A. lucorum DNA detected using the molecular method, combined with the low predation rate in the field-cage experiment, indicated that the primary generalist predators likely had a limited role in the suppression of A. lucorum in the field. © 2016 Society of Chemical Industry.

Methods to identify the prey of invertebrate predators in terrestrial field studies

Predation is an interaction during which an organism kills and feeds on another organism. Past and current interest in studying predation in terrestrial habitats has yielded a number of methods to assess invertebrate predation events in terrestrial ecosystems. We provide a decision tree to select appropriate methods for individual studies. For each method, we then present a short introduction, key examples for applications, advantages and disadvantages, and an outlook to future refinements. Video and, to a lesser extent, live observations are recommended in studies that address behavioral aspects of predator–prey interactions or focus on per capita predation rates. Cage studies are only appropriate for small predator species, but often suffer from a bias via cage effects. The use of prey baits or analyses of prey remains are cheaper than other methods and have the potential to provide per capita predation estimates. These advantages often come at the cost of low taxonomic specificity. Molecular methods provide reliable estimates at a fine level of taxonomic resolution and are free of observer bias for predator species of any size. However, the current PCR‐based methods lack the ability to estimate predation rates for individual predators and are more expensive than other methods. Molecular and stable isotope analyses are best suited to address systems that include a range of predator and prey species. Our review of methods strongly suggests that while in many cases individual methods are sufficient to study specific questions, combinations of methods hold a high potential to provide more holistic insights into predation events. This review presents an overview of methods to researchers that are new to the field or to particular aspects of predation ecology and provides recommendations toward the subset of suitable methods to identify the prey of invertebrate predators in terrestrial field research.

Overcoming PCR Inhibition During DNA-Based Gut Content Analysis of Ants

Generalist predators play an important role in many terrestrial systems, especially within agricultural settings, and ants (Hymenoptera: Formicidae) often constitute important linkages of these food webs, as they are abundant and influential in these ecosystems. Molecular gut content analysis provides a means of delineating food web linkages of ants based on the presence of prey DNA within their guts. Although this method can provide insight, its use on ants has been limited, potentially due to inhibition when amplifying gut content DNA. We designed a series of experiments to determine those ant organs responsible for inhibition and identified variation in inhibition among three species (Tetramorium caespitum (L.), Solenopsis invicta Buren, and Camponotus floridanus (Buckley)). No body segment, other than the gaster, caused significant inhibition. Following dissection, we determined that within the gaster, the digestive tract and crop cause significant levels of inhibition. We found significant differences in the frequency of inhibition between the three species tested, with inhibition most evident in T. caespitum The most effective method to prevent inhibition before DNA extraction was to exude crop contents and crop structures onto UV-sterilized tissue. However, if extracted samples exhibit inhibition, addition of bovine serum albumin to PCR reagents will overcome this problem. These methods will circumvent gut content inhibition within selected species of ants, thereby allowing more detailed and reliable studies of ant food webs. As little is known about the prevalence of this inhibition in other species, it is recommended that the protocols in this study are used until otherwise shown to be unnecessary.

Elucidating the Common Generalist Predators of Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae) in an Organic Apple Orchard Using Molecular Gut-Content Analysis

Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), plum curculio, is a serious direct pest of North American tree fruit including, apples, cherries, peaches and plums. Historically, organophosphate insecticides were used for control, but this tool is no longer registered for use in tree fruit. In addition, few organically approved insecticides are available for organic pest control and none have proven efficacy as this time. Therefore, promoting biological control in these systems is the next step, however, little is known about the biological control pathways in this system and how these are influenced by current mechanical and cultural practices required in organic systems. We used molecular gut-content analysis for testing field caught predators for feeding on plum curculio. During the study we monitored populations of plum curculio and the predator community in a production organic apple orchard. Predator populations varied over the season and contained a diverse assemblage of spiders and beetles. A total of 8% of all predators (eight Araneae, two Hemiptera, and six Coleoptera species) assayed for plum curculio predation were observed positive for the presence of plum curculio DNA in their guts, indicating that these species fed on plum curculio prior to collection Results indicate a number of biological control agents exist for this pest and this requires further study in relation to cultural practices.

Administering and Detecting Protein Marks on Arthropods for Dispersal Research

Monitoring arthropod movement is often required to better understand associated population dynamics, dispersal patterns, host plant preferences, and other ecological interactions. Arthropods are usually tracked in nature by tagging them with a unique mark and then re-collecting them over time and space to determine their dispersal capabilities. In addition to actual physical tags, such as colored dust or paint, various types of proteins have proven very effective for marking arthropods for ecological research. Proteins can be administered internally and/or externally. The proteins can then be detected on recaptured arthropods with a protein-specific enzyme-linked immunosorbent assay (ELISA). Here we describe protocols for externally and internally tagging arthropods with protein. Two simple experimental examples are demonstrated: (1) an internal protein mark introduced to an insect by providing a protein-enriched diet and (2) an external protein mark topically applied to an insect using a medical nebulizer. We then relate a step-by-step guide of the sandwich and indirect ELISA methods used to detect protein marks on the insects. In this demonstration, various aspects of the acquisition and detection of protein markers on arthropods for mark-release-recapture, mark-capture, and self-mark-capture types of research are discussed, along with the various ways that the immunomarking procedure has been adapted to suit a wide variety of research objectives.

Is Vector Control Sufficient to Limit Pathogen Spread in Vineyards?

Vector control is widely viewed as an integral part of disease management. Yet epidemiological theory suggests that the effectiveness of control programs at limiting pathogen spread depends on a variety of intrinsic and extrinsic aspects of a pathosystem. Moreover, control programs rarely evaluate whether reductions in vector density or activity translate into reduced disease prevalence. In areas of California invaded by the glassy-winged sharpshooter (Homalodisca vitripennis Germar), Pierce's disease management relies heavily on chemical control of this vector, primarily via systemic conventional insecticides (i.e., imidacloprid). But, data are lacking that attribute reduced vector pressure and pathogen spread to sharpshooter control. We surveyed 34 vineyards over successive years to assess the epidemiological value of within-vineyard chemical control. The results showed that imidacloprid reduced vector pressure without clear nontarget effects or secondary pest outbreaks. Effects on disease prevalence were more nuanced. Treatment history over the preceding 5 yr affected disease prevalence, with significantly more diseased vines in untreated compared with regularly or intermittently treated vineyards. Yet, the change in disease prevalence between years was low, with no significant effects of insecticide treatment or vector abundance. Collectively, the results suggest that within-vineyard applications of imidacloprid can reduce pathogen spread, but with benefits that may take multiple seasons to become apparent. The relatively modest effect of vector control on disease prevalence in this system may be attributable in part to the currently low regional sharpshooter population densities stemming from area-wide control, without which the need for within-vineyard vector control would be more pronounced.

Knowing your enemies: Integrating molecular and ecological methods to assess the impact of arthropod predators on crop pests

The importance of natural enemies as the foundation of integrated pest management (IPM) is widely accepted, but few studies conduct the manipulative field experiments necessary to directly quantify their impact on pest populations in this context. This is particularly true for predators. Studying arthropod predator-prey interactions is inherently difficult: prey items are often completely consumed, individual predator-prey interactions are ephemeral (rendering their detection difficult) and the typically fluid or soft-bodied meals cannot be easily identified visually within predator guts. Serological techniques have long been used in arthropod predator gut-contents analysis, and current enzyme linked immunosorbent assays (ELISA) are highly specific and sensitive. Recently, polymerase chain reaction (PCR) methods for gut-contents analysis have developed rapidly and they now dominate the diagnostic methods used for gut-contents analysis in field-based research. This work has identified trophic linkages within food webs, determined predator diet breadth and preference, demonstrated the importance of cannibalism and intraguild predation within and between certain taxa, and confirmed the benefits (predator persistence) and potential disadvantages (reduced feeding on pest species) of the availability of alternative nonpest prey. Despite considerable efforts to calibrate gut-contents assays, these methods remain qualitative. Available techniques for predator gut-contents analysis can provide rapid, accurate, cost-effective identification of predation events. As such, they perfectly compliment the ecological methods developed to directly assess predator impacts on prey populations but which are imperfect at identifying the key predators. These diagnostic methods for gut-contents analysis are underexploited in agricultural research and they are almost never applied in unison with the critical field experiments to measure predator impact. This paper stresses the need for a combined approach and suggests a framework that would make this possible, so that appropriate natural enemies can be targeted in conservation biological control.

Molecular diagnosis of bird-mediated pest consumption in tropical farmland

Biodiversity loss will likely have surprising and dramatic consequences for human wellbeing. Identifying species that benefit society represents a critical first step towards predicting the consequences of biodiversity loss. Though natural predators prevent billions of dollars in agricultural pest damage annually, characterizing which predators consume pests has proven challenging. Emerging molecular techniques may illuminate these interactions. In the countryside of Costa Rica, we identified avian predators of coffee's most damaging insect pest, the coffee berry borer beetle (Coleoptera:Scolytidae Hypothenemus hampeii), by assaying 1430 fecal samples of 108 bird species for borer DNA. While feeding trials confirmed the efficacy of our approach, detection rates were low. Nevertheless, we identified six species that consume the borer. These species had narrow diet breadths, thin bills, and short wings; traits shared with borer predators in other systems. Borer predators were not threatened; therefore, safeguarding pest control necessitates managing species beyond those at risk of regional extinction by maintaining populations in farmland habitats. Generally, our results demonstrate potential for pairing molecular methods with ecological analyses to yield novel insights into species interactions.

Predator community structure and trophic linkage strength to a focal prey

Predator abundance and community structure can affect the suppression of lower trophic levels, although studies of these interactions under field conditions are relatively few. We investigated how the frequency of consumption (measured using PCR-based gut content analysis) is affected by predator abundance, community diversity and evenness under realistic conditions. Soil arthropod communities in sixteen maize fields were measured (number of predators, diversity [Shannon H] and evenness [J]), and predator guts were searched for DNA of the focal subterranean herbivore, the corn rootworm (Diabrotica virgifera). Predator abundance and diversity were positively correlated with trophic linkage strength (the proportion positive for rootworm DNA), although the latter characteristic was not significantly so. The diversity and evenness of the predator community with chewing mouthparts were strongly correlated with their linkage strength to rootworms, whereas the linkage strength of fluid-feeding predators was unaffected by their community characteristics. Within this community, chewing predators are more affected by the rootworm's hemolymph defence. This research clearly shows that predator abundance and diversity influence the strength of a community's trophic linkage to a focal pest and that these community characteristics may be particularly important for less palatable or protected prey species. We also make the case for conserving diverse and abundant predator communities within agroecosystems as a form of pest management.

Resolving multiple host use of an emergent pest of cotton with microsatellite data and chloroplast markers (Creontiades dilutus Stål; Hemiptera, Miridae)

Following the global uptake of transgenic cotton several Hemipteran pests have emerged as primary targets for pesticide control. Previous research on one such emergent pest: the green mirid, Creontiades dilutus, indicated differential use of two crop hosts, cotton (Gossypium hirsutum, Malvaceae) and lucerne (alfalfa) (Medicago sativa, Fabaceae). We tested the hypothesis that this apparent demographic independence of lucerne and cotton inhabiting mirids is the result of cryptic species being associated with these two crops. We assessed gene flow using microsatellite markers across adjacent cotton and lucerne crops at three geographically separated sites (up to 900 km apart). We also analysed the recent feeding behaviour of these insects by amplifying chloroplast markers from their gut contents. We find high gene flow between these two crops (mean pair wise F ST between host plants=0.0141 within localities), and no evidence of cryptic species. Furthermore, the gut analyses revealed evidence of substantial recent movement between these two crops. We discuss the implications of these results for interpreting multiple host use in this species and setting future research priorities for this economically important pest.

Molecular interrogation of the feeding behaviour of field captured individual insects for interpretation of multiple host plant use

The way in which herbivorous insect individuals use multiple host species is difficult to quantify under field conditions, but critical to understanding the evolutionary processes underpinning insect–host plant relationships. In this study we developed a novel approach to understanding the host plant interactions of the green mirid, Creontiades dilutus, a highly motile heteropteran bug that has been associated with many plant species. We combine quantified sampling of the insect across its various host plant species within particular sites and a molecular comparison between the insects' gut contents and available host plants. This approach allows inferences to be made as to the plants fed upon by individual insects in the field. Quantified sampling shows that this “generalist” species is consistently more abundant on two species in the genus Cullen (Fabaceae), its primary host species, than on any other of its numerous listed hosts. The chloroplast intergenic sequences reveal that C. dilutus frequently feeds on plants additional to the one from which it was collected, even when individuals were sampled from the primary host species. These data may be reconciled by viewing multiple host use in this species as an adaptation to survive spatiotemporally ephemeral habitats. The methodological framework developed here provides a basis from which new insights into the feeding behaviour and host plant relationships of herbivorous insects can be derived, which will benefit not only ecological interpretation but also our understanding of the evolution of these relationships.

Transgenic Cry1Ab rice does not impact ecological fitness and predation of a generalist spider

Background

The commercial release of rice genetically engineered to express a Cry1Ab protein from Bacillus thuringiensis (Bt) for control of Lepidoptera in China is a subject of debate. One major point of the debate has focused on the ecological safety of Bt rice on nontarget organisms, especially predators and parasitoids that help control populations of insect pests.

Methodology/Principal Findings

A tritrophic bioassay was conducted to evaluate the potential impact of Cry1Ab-expressing rice on fitness parameters of a predaceous ground spider (Pardosa pseudoannulata (Bösenberg et Strand)) that had fed on Bt rice-fed brown planthopper (Nilaparvata lugens (Stål)) nymphs. Survival, development time and fecundity of this spider were not different when they were fed with Bt rice-fed or non-Bt rice-fed prey. Furthermore, ELISA and PCR gut assays, as well as a functional response trial, indicated that predation by P. pseudoannulata was not significantly different in Bt rice or non-Bt rice fields.

Conclusions/Significance

The transgenic Cry1Ab rice lines tested in this study had no adverse effects on the survival, developmental time and fecundity of P. pseudoannulata in the laboratory or on predation under field conditions. This suggests that this important predator would not be harmed if transgenic Cry1Ab rice were commercialized.

DNA-based analysis of regurgitates: a noninvasive approach to examine the diet of invertebrate consumers

DNA-based gut content analysis has become an important tool for unravelling feeding interactions in invertebrate communities under natural conditions. It usually implies killing of the consumer and extracting the DNA from its food, using either the whole animal or its dissected gut. This post-mortem approach, however, is not suitable for investigating the diet of rare or protected species and also prohibits tracking individual dietary preferences as each consumer can provide trophic information only once. Moreover, removing large numbers of consumers from a habitat for analysis might critically change population densities and affect species interactions. Here, we present DNA-based analysis of invertebrate regurgitates, a novel approach to overcome these limitations. Conducting feeding experiments where adult Poecilus cupreus (Coleoptera: Carabidae) were fed with larvae of Amphimallon solstitiale (Coleoptera: Scarabaeidae), we show that detection success in regurgitates compared to samples prepared from whole beetles was similar or significantly enhanced for small/medium and large prey DNA fragments, respectively. Prey DNA detection success remained high in regurgitates stored in ethanol for 21 months at room temperature prior to DNA extraction. We conclude that in those invertebrates where regurgitates can be obtained, examination of food DNA in regurgitates offers many advantages over conventional post-mortem gut content analysis.

Removing external DNA contamination from arthropod predators destined for molecular gut-content analysis

Ecological research requires large samples for statistical validity, typically hundreds or thousands of individuals, which are most efficiently gathered by mass-collecting techniques. For the study of interspecific interactions, molecular gut-content analysis enables detection of arthropod predation with minimal disruption of community interactions. Field experiments have demonstrated that standard mass-collection methods, such as sweep netting, vacuum sampling and foliage beating, sometimes lead to contamination of predators with nontarget DNA, thereby compromising resultant gut-content data. We deliberately contaminated immature Coleomegilla maculata and Podisus maculiventris that had been fed larvae of Leptinotarsa decemlineata by topically applying homogenate of the alternate prey Leptinotarsa juncta. We then attempted to remove contaminating DNA by washing in ethanol or bleach. A 40-min wash with end-over-end rotation in 80% EtOH did not reliably reduce external DNA contamination. Identical treatment with 2.5% commercial bleach removed most externally contaminating DNA without affecting the detectability of the target prey DNA in the gut. Use of this bleaching protocol, perhaps with minor modifications tailored to different predator-prey systems, should reliably eliminate external DNA contamination, thereby alleviating concerns about this possible source of cross-contamination for mass-collected arthropod predators destined for molecular gut-content analysis.

A molecular approach to identifying the natural prey of the African creeping water bug Naucoris, a potential reservoir of Mycobacterium ulcerans

The extra-oral digestion of creeping water bugs (Naucoridae: Hemiptera) hinders the study of their diet using the standard method of identifying prey body parts in the gut. Genetic methods are available, but rely on PCR tests or similar diagnostics to confirm suspected prey. Where the potential prey is unknown and a broad search for all possible prey is desirable, methods that can potentially capture any prey item are required. Naucoris sp. is known to harbor Mycobacterium ulcerans (Actinomycetales: Mycobacteriaceae), the causative bacterium of Buruli ulcer. Outbreaks of Buruli ulcer have been associated with disturbed freshwater habitats, but the mode of transmission to humans remains unclear. Here we examine the diet of Naucoris sp., a dominant aquatic predator in water bodies in Ghana where the prevalence of Buruli ulcer is high. We cloned and sequenced 576 PCR products (mtDNA rrnL, cox1) isolated from the gut of 60 Naucoris sp. individuals to determining diet composition as broadly as possible. Using phylogenetic analysis of newly sequenced clones and 6 potential prey taxa collected from the site, sequences isolated from Naucoris sp. guts matched locally collected Coleoptera (Hydrophilidae). Blastn queries to GenBank of other clone sequences produced matches to (Anura) (n = 1), Rotifera (n = 5), and fungi (n = 4) as additional components of the diet. Our results suggest that sp. in this Buruli ulcer-endemic area feeds on a wide range of prey and body sizes, and that the approach could be successfully applied to studies of aquatic food webs where morphological identification of prey is impossible and where little or no a priori knowledge is available.

The ubiquity of intraguild predation among predatory arthropods

Intraguild predation (IGP) occurs when one predator species attacks another predator species with which it competes for a shared prey species. Despite the apparent omnipresence of intraguild interactions in natural and managed ecosystems, very few studies have quantified rates of IGP in various taxa under field conditions. We used molecular analyses of gut contents to assess the nature and incidence of IGP among four species of coccinellid predators in soybean fields. Over half of the 368 predator individuals collected in soybean contained the DNA of other coccinellid species indicating that IGP was very common at our field site. Furthermore, 13.2% of the sampled individuals contained two and even three other coccinellid species in their gut. The interaction was reciprocal, as each of the four coccinellid species has the capacity to feed on the others. To our knowledge, this study represents the most convincing field evidence of a high prevalence of IGP among predatory arthropods. The finding has important implications for conservation biology and biological control.

Prey DNA detection success following digestion by intraguild predators: influence of prey and predator species

Intraguild predation (IGP) has been increasingly recognized as an important interaction in ecological systems over the past two decades, and remarkable insights have been gained into its nature and prevalence. We have developed a technique using molecular gut-content analysis to compare the rate of IGP between closely related species of coccinellid beetles (lady beetles or ladybirds), which had been previously known to prey upon one another. We first developed PCR primers for each of four lady beetle species: Harmonia axyridis, Coccinella septempunctata, Coleomegilla maculata and Propylea quatuordecimpunctata. We next determined the prey DNA detection success over time (DS(50) ) for each combination of interacting species following a meal. We found that DS(50) values varied greatly between predator-prey combinations, ranging from 5.2 to 19.3 h. As a result, general patterns of detection times based upon predator or prey species alone are not discernable. We used the DS(50) values to correct field data to demonstrate the importance of compensation for detection times that are specific to particular predator-prey combinations.

A method for distinctly marking honey bees, Apis mellifera, originating from multiple apiary locations

Inexpensive and non-intrusive marking methods are essential to track natural behavior of insects for biological experiments. An inexpensive, easy to construct, and easy to install bee marking device is described in this paper. The device is mounted at the entrance of a standard honey bee Apis mellifera L. (Hymenoptera: Apidae) hive and is fitted with a removable tube that dispenses a powdered marker. Marking devices were installed on 80 honey bee colonies distributed in nine separate apiaries. Each device held a tube containing one of five colored fluorescent powders, or a combination of a fluorescent powder (either green or magenta) plus one of two protein powders, resulting in nine unique marks. The powdered protein markers included egg albumin from dry chicken egg whites and casein from dry powdered milk. The efficacy of the marking procedure for each of the unique markers was assessed on honey bees exiting each apiary. Each bee was examined, first by visual inspection for the presence of colored fluorescent powder and then by egg albumin and milk casein specific enzyme-linked immunosorbent assays (ELISA). Data indicated that all five of the colored fluorescent powders and both of the protein powders were effective honey bee markers. However, the fluorescent powders consistently yielded more reliable marks than the protein powders. In general, there was less than a 1% chance of obtaining a false positive colored or protein-marked bee, but the chance of obtaining a false negative marked bee was higher for "protein-marked" bees.

Unnecessary roughness? Testing the hypothesis that predators destined for molecular gut-content analysis must be hand-collected to avoid cross-contamination

Molecular gut-content analysis enables detection of arthropod predation with minimal disruption of ecosystem processes. Mass-collection methods, such as sweep-netting, vacuum sampling and foliage beating, could lead to regurgitation or rupturing of predators along with uneaten prey, thereby contaminating specimens and compromising resultant gut-content data. Proponents of this 'cross-contamination hypothesis' advocate hand-collection as the best way to avoid cross-contamination. However, hand-collection is inefficient when large samples are needed, as with most ecological research. We tested the cross-contamination hypothesis by setting out onto potato plants immature Coleomegilla maculata and Podisus maculiventris that had been fed larvae of either Leptinotarsa decemlineata or Leptinotarsa juncta, or unfed individuals of these predator species along with L. decemlineata larvae. The animals were then immediately re-collected, either by knocking them vigorously off the plants onto a beat cloth and capturing them en masse with an aspirator ('rough' treatment) or by hand-searching and collection with a brush ('best practice'). Collected predators were transferred in the field to individual vials of chilled ethanol and subsequently assayed by PCR for fragments of cytochrome oxidase I of L. decemlineata and L. juncta. Ten to 39 per cent of re-collected fed predators tested positive by PCR for DNA of both Leptinotarsa species, and 14-38% of re-collected unfed predators contained L. decemlineata DNA. Overall levels of cross-contamination in the rough (31%) and best-practice (11%) samples were statistically different and supported the cross-contamination hypothesis. A pilot study on eliminating external DNA contamination with bleach prior to DNA extraction and amplification gave promising results.

Distribution of glassy-winged sharpshooter and threecornered alfalfa hopper on plant hosts in the San Joaquin Valley, California

Homalodisca vitripennis (Germar) and Spissistilus festinus (Say) populations were surveyed bimonthly for 14 mo in Kern County, CA, at five agricultural sites made up of a variety of potential host plants. In addition, S. festinus populations were surveyed in four alfalfa, Medicago sativa L., fields in Kern and Tulare counties. Insects were collected by beats-sweeps and sticky traps. Data on host plant condition and phenology, and ground cover presence and composition were collected at the five agricultural sites, whereas data on mowing and insecticide use were collected at the four alfalfa sites. Populations of both insects persisted at the five agricultural locations despite insecticide applications applied as part of a H. vitripennis areawide management program and standard commercial operations. Plants colonized by H. vitripennis included eucalyptus (Eucalyptus L'Hér.), jojoba [Simmondsia chinensis (Link) C. K. Schneid.], and citrus (Citrus spp.). Populations of S. festinus were much greater in collections from alfalfa fields than from the five agricultural sites. Insects collected from the five mixed agricultural sites were negative for presence of X. fastidiosa. In laboratory tests, S. festinus did not acquire or transmit X. fastidiosa in tests with infected grape (Vitis spp.) as an acquisition source and grape, almond [Prunus dulcis (Mill.) D.A.Webb], and alfalfa as inoculation hosts. Recommendations for vector control, vegetation management, and targeted monitoring to reduce insect populations and inoculum potential are discussed.

Molecular markers discriminate closely related species Encarsia diaspidicola and Encarsia berlesei (Hymenoptera: Aphelinidae): biocontrol candidate agents for white peach scale in Hawaii

We genetically characterized Encarsia diapsidicola Silvestri and Encarsia berlesei Howard (Hymenoptera: Aphelinidae) by two molecular methods: phylogenetic analysis of the cytochrome oxidase subunit I gene (COI) and intersimple sequence repeat-polymerase chain reaction (ISSR-PCR) DNA fingerprinting. These two closely related endoparasitoids are candidate biological control agents for the white peach scale, Pseudaulacaspis pentagona Targioni-Tozetti (Hemiptera: Diaspididae), in Hawaii. We developed species-specific COI molecular markers that discriminated the two species, and we tested the utility of the E. diaspidicola-specific COI marker to detect parasitism of white peach scale. The COI sequence data uncovered 46-bp differences between the two Encarsia spp. The level of COI genetic divergence between the two species was 9.7%, and the two clustered into their own clade on a parismonious phylogram. ISSR-PCR readily discriminated the two Encarsia spp. because each was observed with fixed species-specific banding patterns. The COI molecular markers were specific for each species because cross-reactivity was not observed with nontarget species. The E. diaspidicola-specific COI markers were successful at detecting parasitism of white peach scale by E. diaspidicola by 24 h. Both molecular marker types successfully discriminated the two Encarsia spp., whereas the COI markers will be useful as tools to assess levels of parasitism in the field and to study competitive interactions between parasitoids.

Tracking medfly predation by the wolf spider, Pardosa cribata Simon, in citrus orchards using PCR-based gut-content analysis

The Mediterranean fruit fly, Ceratitis capitata (Wiedemann), which is often controlled chemically, is a major citrus pest in Spain; however, alternative biological control strategies such as those based on the conservation of polyphagous predators should be developed. The wolf spider, Pardosa cribata Simon, is an abundant predator found in citrus orchards in eastern Spain. In this study, we have evaluated polymerase chain reaction (PCR)-based techniques as a means of detecting C. capitata DNA remains in P. cribata specimens. To do so, two pairs of C. capitata species-specific primers were designed and tested. Primer specificity was tested on species closely related to C. capitata and with other pests and natural enemies present in citrus orchards. Medfly DNA was detectable in 100% of P. cribata from 0 to 12 h post ingestion for both primer pairs, decreasing to 37% at 96 h after prey ingestion for one pair of primers. DNA detectability half-lives were of 78.25 h and 78.08 h for each pair of primers but no statistical differences were found between them. Pardosa cribata specimens were field-collected daily after sterile C. capitata pupae had been deployed in the citrus orchard. Afterwards, the wolf spiders were analyzed and DNA remains of C. capitata were detected in 5% of them, with a peak of 15% coinciding with maximum C. capitata emergence. This study is the first to reveal the potential use of DNA markers to track medfly predation by P. cribata in citrus orchards and provides a new tool to estimate the potential role of this spider in biological-control conservation programs.

Molecular diagnosis of a previously unreported predator-prey association in coffee: Karnyothrips flavipes Jones (Thysanoptera: Phlaeothripidae) predation on the coffee berry borer

The coffee berry borer, Hypothenemus hampei, is the most important pest of coffee throughout the world, causing losses estimated at US $500 million/year. The thrips Karnyothrips flavipes was observed for the first time feeding on immature stages of H. hampei in April 2008 from samples collected in the Kisii area of Western Kenya. Since the trophic interactions between H. hampei and K. flavipes are carried out entirely within the coffee berry, and because thrips feed by liquid ingestion, we used molecular gut-content analysis to confirm the potential role of K. flavipes as a predator of H. hampei in an organic coffee production system. Species-specific COI primers designed for H. hampei were shown to have a high degree of specificity for H. hampei DNA and did not produce any PCR product from DNA templates of the other insects associated with the coffee agroecosystems. In total, 3,327 K. flavipes emerged from 17,792 H. hampei-infested berries collected from the field between April and September 2008. Throughout the season, 8.3% of K. flavipes tested positive for H. hampei DNA, although at times this figure approached 50%. Prey availability was significantly correlated with prey consumption, thus indicating the potential impact on H. hampei populations.