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The Ichneumonoidea is a vast and important superfamily of parasitic wasps, with some 60,000 described species and estimated numbers far higher, especially for small-bodied tropical taxa. The superfamily comprises two cosmopolitan families - Braconidae and Ichneumonidae - that have largely attracted separate groups of researchers, and this, to a considerable extent, has meant that understanding of their adaptive features has often been considered in isolation. This book considers both families, highlighting similarities and differences in their adaptations. The classification of the whole of the Ichneumonoidea, along with most other insect orders, has been plagued by typology whereby undue importance has been attributed to particular characters in defining groups. Typology is a common disease of traditional taxonomy such that, until recently, quite a lot of taxa have been associated with the wrong higher clades. The sheer size of the group, and until the last 30 or so years, lack of accessible identification materials, has been a further impediment to research on all but a handful of 'lab rat' species usually cultured initially because of their potential in biological control. New evidence, largely in the form of molecular data, have shown that many morphological, behavioural, physiological and anatomical characters associated with basic life history features, specifically whether wasps are ecto- or endoparasitic, or idiobiont or koinobiont, can be grossly misleading in terms of the phylogeny they suggest. This book shows how, with better supported phylogenetic hypotheses entomologists can understand far more about the ways natural selection is acting upon them. This new book also focuses on this superfamily with which the author has great familiarity and provides a detailed coverage of each subfamily, emphasising  anatomy, taxonomy and systematics, biology, as well as pointing out the importance and research potential of each group. Fossil taxa are included and it also has sections on biogeography, global species richness, culturing and rearing and preparing specimens for taxonomic study. The book highlights areas where research might be particularly rewarding and suggests systems/groups that need investigation. The author provides a large compendium of references to original research on each group. This book is an essential workmate for all postgraduates and researchers working on ichneumonoid or other parasitic wasps worldwide. It will stand as a reference book for a good number of years, and while rapid advances in various fields such as genomics and host physiological interactions will lead to new information, as an overall synthesis of the current state it will stay relevant for a long time.

[This corrects the article DOI: 10.1371/journal.pone.0180729.].

Colonies of house flies (Musca domestica L. [Diptera: Muscidae]) and four species of parasitoids (Muscidifurax raptor Girault and Sanders, Muscidifurax zaraptor Kogan and Legner, Spalangia cameroni Perkins and Spalangia endius Walker) were established by making collections from dairy farms near Bell, FL, Beatrice, NE, Minneapolis, MN, and San Jacinto, CA. Colonies were assessed for heat tolerance by comparing life history parameters at 25–27°C and fluctuating hot (26.7–41.7°C) temperatures. Muscidifurax raptor, S. cameroni, and S. endius produced 24–28% as many progeny under hot conditions as at 25°C. Colonies of M. zaraptor were more heat-tolerant and produced an average 46.9% as many progeny under the hot regime compared with moderate conditions. There was little evidence for higher heat tolerance in parasitoid populations from historically hot locations (CA desert and FL). Colonies of M. raptor and S. endius that had been in culture for 24 yr were the least heat-tolerant with regard to progeny production. House flies collected from the same locations varied little in longevity, fecundity, or egg-to-adult survival under either hot or moderate regimes. Flies reared under hot conditions laid about half as many eggs (89/female) and had about half the egg–adult survival rate (47.3%) under hot compared with moderate conditions, indicating that heat stress had less effect on flies than on all of the parasitoids except M. zaraptor. An attempt to select for heat tolerance in flies by subjecting them to incremental increases in rearing temperatures for 20 generations resulted in little change in tolerance among the selected flies.

Symbiotic microbes have become increasingly recognized to mediate interactions between natural enemies and their hosts. The ecologies of these symbioses, however, are poorly understood in many systems, and a predictive framework is needed to guide future studies. To achieve this, we focus on heritable, defensive microbes of insects. Our review of laboratory‐based studies identifies diverse bacterial species that have independently evolved to protect a range of insects against parasitoids, parasites, predators and pathogens. Although defensive mechanisms are typically unknown, some involve toxins or the upregulation of host immunity. Despite substantial benefits of infection in the presence of natural enemies, the protective symbionts of insects are often found at intermediate levels in natural populations. Using a host‐centred population genetics approach made possible by the host restriction and cytoplasmic inheritance of these microbes, we propose that balancing selection plays a major role in symbiont maintenance, with protective benefits in the presence of enemies and infection costs in their absence. Other mediating factors are likely to be important, including temperature, superinfections and transmission dynamics. While few studies have provided evidence for defence in the field, several studies have shown symbiont infection frequencies to be dynamic, varying across temporal and spatial gradients and food–plant associations. Newly presented data from our pea aphid research reveal that temporal shifts in defensive symbiont prevalence can be quite rapid, with Hamiltonella defensa showing 10–20% shifts around a seasonal average of c. 50%. Such findings contrast with more unidirectional changes seen in laboratory population cages, suggesting temporal changes in the costs and benefits of symbionts in the field. To frame future research on defensive symbiont ecology, we briefly consider a range of studies needed to test laboratory‐ and field‐derived predictions on defensive symbiosis. Included are investigations of defensive mechanisms, symbiont‐driven co‐evolution and community‐level effects. We also consider the need for more thorough and highly resolved molecular diagnostics of natural infections, laboratory studies on functional differences between symbiont strains and species and studies on the relative costs and benefits of defenders in nature. The emerging theme of symbiont‐mediated defence across eukaryotes suggests that knowledge of the functional mechanisms behind protection and natural symbiont dynamics could be key to understanding many of the world's antagonistic species interactions. Thus, the development of insects as a model for such studies holds promise for these organisms and beyond.

Parasitoids induce physiological changes in their herbivorous hosts that affect how plants respond to herbivory. The signature of parasitoids on induced plant responses to feeding by parasitized herbivores indirectly impacts insect communities interacting with the plant. The effect may extend to parasitoids and cause indirect interaction between parasitoids that develop inside different herbivore hosts sharing the food plant. However, this type of interactions among parasitoid larvae has received very little attention. In this study, we investigated sequential and simultaneous plant-mediated interactions among two host–parasitoid systems feeding on Brassica oleracea plants: Mamestra brassicae parasitized by Microplitis mediator and Pieris rapae parasitized by Cotesia rubecula. We measured the mortality, development time, and weight of unparasitized herbivores and performance of parasitoids that had developed inside the two herbivore species when sharing the food plant either simultaneously or sequentially. Plant induction by parasitized or unparasitized hosts had no significant effect on the performance of the two herbivore host species. In contrast, the two parasitoid species had asymmetrical indirect plant-mediated effects on each other’s performance. Cotesia rubecula weight was 15% higher on plants induced by M. mediator-parasitized hosts, compared to control plants. In addition, M. mediator development time was reduced by 30% on plants induced by conspecific but not heterospecific parasitoids, compared to plants induced by its unparasitized host. Contrary to sequential feeding, parasitoids had no effect on each other’s performance when feeding simultaneously. These results reveal that indirect plant-mediated interactions among parasitoid larvae could involve any parasitoid species whose hosts share a food plant.

Anastrepha fraterculus (Wiedemann) (Diptera: Tephritidae) is a significant fruit pest of economic and quarantine importance in South America. Biological control using augmentative releases of parasitoids or conservation strategies for these natural enemies are handy tools in integrated fruit fly management programs. The functional response describes the natural enemy consumption rate with increasing resource density. Such information may be relevant for selecting the parasitoid species that is potentially most suitable to serve as a biocontrol agent of A. fraterculus. Furthermore, the number of discarded hosts determined from functional response analysis might be used to estimate suitable host densities, avoiding wastage of larvae/puparia associated with host overproduction. Therefore, the current study aimed to evaluate the functional response of four Neotropical-native parasitoid species commonly associated with species of the Anastrepha genus in the Americas, such as the pupal parasitoid Coptera haywardi (Ogloblin) (Hymenoptera: Diapriidae) and the larval parasitoids Ganaspis pelleranoi (Brèthes) (Hymenoptera: Figitidae), Doryctobracon crawfordi (Viereck), and Opius bellus Gahan (Hymenoptera: Braconidae). The package “frair” from R software was used to determine the functional response type and parameter estimation, enabling selection, fitting, and comparison among standard functional response models and integral parameters. Four relevant conclusions can be highlighted: (a) G. pelleranoi showed a flexible functional response, with a statistically significant deviation to a Type III rather than a Type II response found among the three other parasitoid species; (b) G. pelleranoi had a handling time significantly lower than the other tested parasitoid species; (c) the number of attacked hosts varied among all four parasitoid species, with C. haywardi and G. pelleranoi exhibiting the highest proportion of attacks at low and high host densities, respectively; and (d) the percentage of discarded hosts was significantly low at 1–5 and 1–20 hosts per parasitoid in C. haywardi and G. pelleranoi, respectively, whereas in both D. crawfordi and O. bellus, it was high at any offered host density. Results provide helpful comparative information about the possible performance of these species as biocontrol agents against A. fraterculus populations within augmentative and/or conservative biological control programs.

Parasitoid wasp venoms represent highly specialized biochemical arsenals that evolved to manipulate host physiology and ensure successful development of the parasitoid offspring. However, the molecular targets and mechanisms underlying this complex host modulation remain poorly understood. To address this, we employed an AI-driven discovery pipeline, integrating the sequence-based predictor D-SCRIPT with the structural modeler AlphaFold3, to characterize LjSPI-1, a venom serpin from Liragathis javana. This computational workflow highlighted a previously unreported candidate partner—a host serine carboxypeptidase (Chr09G02510). Crucially, we detected a direct physical interaction between these two proteins through both in vitro pull-down and in vivo yeast two-hybrid assays, supporting this AI-prioritized interaction under experimental conditions. Our study identifies a high-priority molecular pairing and demonstrates the utility of an AI-guided strategy for uncovering candidate targets of venom proteins. In addition, guided by the predicted biochemical role of Chr09G02510, we propose several plausible physiological hypotheses linking this interaction to host peptide metabolism and immune modulation. These hypotheses serve as a conceptual basis for future mechanistic and toxicological investigations.

Invasive species, because of their lack of co-evolutionary history with recipient communities, can act as “evolutionary traps” causing disconnects between natural enemy behavioural responses and the suitability of the invasive species as a prey/host resource. Invasion of exotic species in non-native environments may have several ecological effects, including consequences for the experience-mediated behavioural responses of indigenous foragers. Experience is usually thought to help resident species to buffer against negative impacts of new invasive species, including escaping from evolutionary traps. Here we hypothesized that the impact of foraging experience depends on whether an indigenous egg parasitoid can correctly assess the resource suitability of a new invasive species for offspring development. We showed that the invasive stink bug Halyomorpha halys acts as an evolutionary trap for the indigenous egg parasitoid Trissolcus basalis leading to unsuccessful development of ~ 95% of the eggs laid in this host species. In a mixed scenario in which the associated resident stink bug Nezara viridula co-occurs with the invasive H. halys , we showed that oviposition experience in the low quality invasive host induces in T. basalis similar responses to those of the associated host. These results suggest that foraging experience does not lead to avoidance of an evolutionary trap. We discuss parasitoid foraging experience and reproductive success in the light of the evolutionary trap framework with implication for biological control.

The parasitoid Leptopilina heterotoma has been used as a model system for more than 70 years, contributing greatly to diverse research areas in ecology and evolution. Here, we synthesized the large body of work on L. heterotoma with the aim to identify new research avenues that could be of interest also for researchers studying other parasitoids and insects. We start our review with a description of typical L. heterotoma characteristics, as well as that of the higher taxonomic groups to which this species belongs. We then continue discussing host suitability and immunity, foraging behaviors, as well as fat accumulation and life histories. We subsequently shift our focus towards parasitoid‐parasitoid interactions, including L. heterotoma coexistence within the larger guild of Drosophila parasitoids, chemical communication, as well as mating and population structuring. We conclude our review by highlighting the assets of L. heterotoma as a model system, including its intermediate life history syndromes, the ease of observing and collecting natural hosts and wasps, as well as recent genomic advances. The parasitoid Leptopilina heterotoma has been used as a model system in biology for more than 70 years. This review aims to provide a broad and detailed synthesis of the work performed on this system, including immunity, behavioral ecology, endosymbiotic and trophic interactions, as well as physiology. Overall, the scientific literature on L. heterotoma unites research based on field observations and experiments, as well as laboratory studies, highlighting the versatility of this model system.

The Turkestan cockroach, Blatta lateralis (Walker), is a peridomestic pest of growing concern in the US Southwest. The parasitoid Aprostocetus hagenowii (Ratzburg) is used in IPM programs targeting other blattid cockroach species and may aid in B. lateralis suppression. Information about the ability of A. hagenowii to parasitize B. lateralis is lacking. A no-choice host-switching experiment was used to test A. hagenowii acceptance of B. lateralis oothecae, and a multigenerational no-choice experiment was used to determine the suitability of B. lateralis as a host for A. hagenowii over several months of rearing. Periplaneta americana (L.) (Blattodea: Blattidae), the preferred host of A. hagenowii, and Blatta orientalis L., a known host and relative of B. lateralis, were used for comparison. Development time was similar among hosts and generations (P > 0.05). Parasitism success and proportion of female progeny declined significantly with subsequent generations on both Blatta spp. (parasitism success: χ2 = 14.916; df = 2; P = 0.001; proportion female: H = 6.364; df = 2; P = 0.041). These results suggest that A. hagenowii may initially aid in suppression of B. lateralis, but an overall decline in fitness will require repeated releases or provisioning of P. americana oothecae. Development of a strain more suitable for B. lateralis control may be possible via selection from laboratory strains or through use of wild A. hagenowii from areas where B. lateralis is present.