Un-nesting DNA Russian dolls - the potential for constructing food webs using residual DNA in empty aphid mummies

A molecular approach to unravel trophic interactions between parasitoids and hyperparasitoids associated with pecan aphids

Advances in molecular ecology can overcome many challenges in understanding host-parasitoid interactions. Genetic characterization of the key-players in systems helps to confirm species and identify trophic linkages essential for ecological service delivery by biological control agents; however, relatively few agroecosystems have been explored using this approach. Pecan production consists of a large tree perennial system containing an assortment of seasonal pests and natural enemies. As a first step to characterizing host-parasitoid associations in pecan food webs, we focus on aphid species and their parasitoids. Based on DNA barcoding of field-collected and reared specimens, we confirmed the presence of 3 species of aphid, one family of primary parasitoids, and 5 species of hyperparasitoids. By applying metabarcoding to field-collected aphid mummies, we were able to identify multiple species within each aphid mummy to unravel a complex food web of 3 aphids, 2 primary parasitoids, and upward of 8 hyperparasitoid species. The results of this study demonstrate that multiple hyperparasitoid species attack a single primary parasitoid of pecan aphids, which may have negative consequences for successful aphid biological control. Although further research is needed on a broader spatial scale, our results suggest multiple species exist in this system and may suggest a complex set of interactions between parasitoids, hyperparasitoids, and the 3 aphid species. This was the first time that many of these species have been characterized and demonstrates the application of novel approaches to analyze the aphid-parasitoid food webs in pecans and other tree crop systems.

Diversity of Parasitoid Wasps and Comparison of Sampling Strategies in Rice Fields Using Metabarcoding

A comprehensive and precise evaluation of Arthropoda diversity in agricultural landscapes can enhance biological pest control strategies. We used Malaise traps and sweep nets to collect insects from three double-cropping paddy fields. DNA was extracted from the ethanol preservative of the Malaise traps and from tissue samples of selected parasitoid wasps. This was followed by amplification using DNA barcoding primers to prepare high-throughput sequencing libraries. We annotated a total of 4956 operational taxonomic units (OTUs), encompassing 174 genera and 32 families of parasitoid wasps. The ethanol filter method efficiently captured a wide range of information. However, the method has low resolution and may result in a reduced estimate of species abundance. Additional insect species were also identified in the parasitoid samples. This suggests that high throughput sequencing from adult parasitoid wasps can also detect host species, enabling a better understanding of host species and providing insights into food webs.

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.

Contrasting reproductive traits of competing parasitoids facilitate coexistence on a shared host pest in a biological control perspective

BACKGROUND

Interspecific competition in insect parasitoids is an important ecological phenomenon that has relevant implications for biological pest control. To date, interspecific intrinsic (=larval) competition has been intensively studied, while investigations on extrinsic (=adult) competition have often lagged behind. In this study we examined the role played by parasitoid reproductive traits and host clutch size on the outcome of extrinsic competition between Trissolcus basalis (Wollaston) and Ooencyrtus telenomicida (Vassiliev), two egg parasitoids of the pest Nezara viridula (L). Laboratory experiments were conducted by allowing both parasitoid species to exploit an egg mass made of 10, 20, 30, or 40 hosts through single or simultaneous releases. Furthermore, under field conditions, egg masses consisting of 10 or 40 hosts were exposed in a tomato crop in order to validate laboratory investigation.

RESULTS

The results show that the egg mass size is an important predictor of extrinsic competition in our study system as a higher proportion of T. basalis emerged from large egg masses, while O. telenomicida dominated in small egg masses. Analysis of reproductive traits of parasitoid species indicates that T. basalis has superior abilities in host exploitation compared with O. telenomicida.

CONCLUSIONS

We found that contrasting reproductive traits of two competing egg parasitoid species facilitate coexistence on a shared stink bug host. This work also highlights the importance to consider extrinsic competitive interactions between parasitoid species in a biological control perspective. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The Ecology of Hyperparasitoids

Hyperparasitoids are some of the most diverse members of insect food webs. True hyperparasitoids parasitize the larvae of other parasitoids, reaching these larvae with their ovipositor through the herbivore that hosts the parasitoid larva. During pupation, primary parasitoids also may be attacked by pseudohyperparasitoids that lay their eggs on the parasitoid (pre)pupae. By attacking primary parasitoids, hyperparasitoids may affect herbivore population dynamics, and they have been identified as a major challenge in biological control. Over the past decades, research, especially on aphid- and caterpillar-associated hyperparasitoids, has revealed that hyperparasitoids challenge rules on nutrient use efficiency in trophic chains, account for herbivore outbreaks, or stabilize competitive interactions in lower trophic levels, and they may use cues derived from complex interaction networks to locate their hosts. This review focuses on the fascinating ecology of hyperparasitoids related to how they exploit and locate their often inconspicuous hosts and the insect community processes in which hyperparasitoids are prominent players.

Secondary predation constrains DNA-based diet reconstruction in two threatened shark species

Increasing fishing effort, including bycatch and discard practices, are impacting marine biodiversity, particularly among slow-to-reproduce taxa such as elasmobranchs, and specifically sharks. While some fisheries involving sharks are sustainably managed, collateral mortalities continue, contributing towards > 35% of species being threatened with extinction. To effectively manage shark stocks, life-history information, including resource use and feeding ecologies is pivotal, especially among those species with wide-ranging distributions. Two cosmopolitan sharks bycaught off eastern Australia are the common blacktip shark (Carcharhinus limbatus; globally classified as Near Threatened) and great hammerhead (Sphyrna mokarran; Critically Endangered). We opportunistically sampled the digestive tracts of these two species (and also any whole prey; termed the 'Russian-doll' approach), caught in bather-protection gillnets off northern New South Wales, to investigate the capacity for DNA metabarcoding to simultaneously determine predator and prey regional feeding ecologies. While sample sizes were small, S. mokkaran fed predominantly on stingrays and skates (Myliobatiformes and Rajiformes), but also teleosts, while C. limbatus mostly consumed teleosts. Metabarcoding assays showed extensive intermixing of taxa from the digestive tracts of predators and their whole prey, likely via the predator's stomach chyme, negating the opportunity to distinguish between primary and secondary predation. This Russian-doll effect requires further investigation in DNA metabarcoding studies focussing on dietary preferences and implies that any outcomes will need to be interpreted concomitant with traditional visual approaches.

Species diversity and food web structure jointly shape natural biological control in agricultural landscapes

Land-use change and agricultural intensification concurrently impact natural enemy (e.g., parasitoid) communities and their associated ecosystem services (ESs), i.e., biological pest control. However, the extent to which (on-farm) parasitoid diversity and food webs mediate landscape-level influences on biological control remains poorly understood. Here, drawing upon a 3-year study of quantitative parasitoid-hyperparasitoid trophic networks from 25 different agro-landscapes, we assess the cascading effects of landscape composition, species diversity and trophic network structure on ecosystem functionality (i.e., parasitism, hyperparasitism). Path analysis further reveals cascaded effects leading to biological control of a resident crop pest, i.e., Aphis gossypii. Functionality is dictated by (hyper)parasitoid diversity, with its effects modulated by food web generality and vulnerability. Non-crop habitat cover directly benefits biological control, whereas secondary crop cover indirectly lowers hyperparasitism. Our work underscores a need to simultaneously account for on-farm biodiversity and trophic interactions when investigating ESs within dynamic agro-landscapes.

Hidden Host Mortality from an Introduced Parasitoid: Conventional and Molecular Evaluation of Non-Target Risk

Hidden trophic interactions are important in understanding food web ecology and evaluating the ecological risks and benefits associated with the introduction of exotic natural enemies in classical biological control programs. Although non-target risk is typically evaluated based on evidence of successful parasitism, parasitoid-induced host mortality not resulting in visible evidence of parasitism (i.e., nonreproductive effects) is often overlooked. The adventive establishment of Trissolcus japonicus, an exotic parasitoid of the introduced stink bug Halyomorpha halys, provides an opportunity to investigate the total impact of this parasitoid on target and non-target hosts in the field. We developed a new methodology to measure nonreproductive effects in this system, involving a species-specific diagnostic PCR assay for T. japonicus. We applied this methodology to field-deployed eggs of four pentatomid species, coupled with traditional rearing techniques. Nonreproductive effects were responsible for the mortality of an additional 5.6% of H. halys eggs due to T. japonicus, and were even more substantial in some of the non-target species (5.4-43.2%). The observed hidden mortality of native non-target species from an introduced parasitoid could change predictions about direct and indirect ecological interactions and the efficacy of biological control of the target pest.

Unravelling mummies: cryptic diversity, host specificity, trophic and coevolutionary interactions in psyllid - parasitoid food webs

BACKGROUND

Parasitoids are hyperdiverse and can contain morphologically and functionally cryptic species, making them challenging to study. Parasitoid speciation can arise from specialisation on niches or diverging hosts. However, which process dominates is unclear because cospeciation across multiple parasitoid and host species has rarely been tested. Host specificity and trophic interactions of the parasitoids of psyllids (Hemiptera) remain mostly unknown, but these factors are fundamentally important for understanding of species diversity, and have important applied implications for biological control.

RESULTS

We sampled diverse parasitoid communities from eight Eucalyptus-feeding psyllid species in the genera Cardiaspina and Spondyliaspis, and characterised their phylogenetic and trophic relationships using a novel approach that forensically linked emerging parasitoids with the presence of their DNA in post-emergence insect mummies. We also tested whether parasitoids have cospeciated with their psyllid hosts. The parasitoid communities included three Psyllaephagus morphospecies (two primary and, unexpectedly, one heteronomous hyperparasitoid that uses different host species for male and female development), and the hyperparasitoid, Coccidoctonus psyllae. However, the number of genetically delimited Psyllaephagus species was three times higher than the number of recognisable morphospecies, while the hyperparasitoid formed a single generalist species. In spite of this, cophylogenetic analysis revealed unprecedented codivergence of this hyperparasitoid with its primary parasitoid host, suggesting that this single hyperparasitoid species is possibly diverging into host-specific species. Overall, parasitoid and hyperparasitoid diversification was characterised by functional conservation of morphospecies, high host specificity and some host switching between sympatric psyllid hosts.

CONCLUSIONS

We conclude that host specialisation, host codivergence and host switching are important factors driving the species diversity of endoparasitoid communities of specialist host herbivores. Specialisation in parasitoids can also result in heteronomous life histories that may be more common than appreciated. A host generalist strategy may be rare in endoparasitoids of specialist herbivores despite the high conservation of morphology and trophic roles, and endoparasitoid species richness is likely to be much higher than previously estimated. This also implies that the success of biological control requires detailed investigation to enable accurate identification of parasitoid-host interactions before candidate parasitoid species are selected as biological control agents for target pests.

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.

Intraguild Predation Among Three Common Coccinellids (Coleoptera: Coccinellidae) in China: Detection Using DNA-Based Gut-Content Analysis

The ubiquity of intraguild predation (IGP) has been widely recognized for predatory coccinellids (Coleoptera: Coccinellidae). In Chinese agroecosystems, three species (Coccinella septempunctata L., Harmonia axyridis (Pallas), and Propylea japonica (Thunberg)) are particularly common, but there is little information of interactions occurring between them. In no-choice laboratory feeding trials, differential directional predation was observed between species: C. septempunctata preyed on eggs of P. japonica more than H. axyridis and H. axyridis consumed eggs of C. septempunctata and P. japonica equally, whereas P. japonica had a very low predation rate on eggs of the other two species. In choice trials, C. septempunctata and P. japonica larvae preyed less on H. axyridis eggs than those of P. japonica and C. septempunctata, respectively, contrasting with H. axyridis larvae, which showed similar preference for both species. Species-specific primers were developed for each coccinellid and used to determine the relative frequency of prey consumption in the field. Prior to field-based analysis, primer specificity was confirmed and consumption of prey elicited a positive reaction success, and detection time varied between different predator-prey combinations. Predators were then collected from cotton agroecosystems and, interestingly, no DNA of C. septempunctata was found in P. japonica, but all other predator-prey combinations yielded positive documentation of IGP in the field, with the greatest rate of 9% of C. septempunctata testing positive for H. axyridis DNA. This study confirmed the frequency of IGP among three common coccinellids in Chinese agroecosystems and the likelihood for interference to the biological control services provided by these important natural enemies.

Interspecific competition/facilitation among insect parasitoids

Competition for limited resources is a widespread ecological interaction in animals. In the case of insect parasitoids, species can compete for host resources both at the adult stage as well as at the larval stage. Interspecific competition can play a role in sizing and shaping community structures. In addition of being relevant for basic ecological studies, understanding how interspecific competition between parasitoids affects pest suppression is important for biological control. In this opinion paper we review recent advances in the field of interspecific competition among parasitoids in a biological control perspective. We first discuss adult competition, highlighting which factors are likely to play a role in the outcome of competition when adults interact either directly or indirectly. Then we focus on the interactions occurring between competing larvae that develop within the same host taking also into account the fitness consequences of competition for the larva surviving interspecific competition. We also explore the possibility of interspecific facilitation among parasitoids in those situations in which a given species may benefit from interspecific competition.