Cynipidae Research Articles

Comparative anatomy of venom glands suggests a role of maternal secretions in gall induction by cynipid wasps (Hymenoptera: Cynipidae)

Abstract Many herbivorous insect species are capable of hijacking plant development to induce novel plant organs called galls. In most groups of galling insects, the insect organs and molecular signals involved in gall induction are poorly understood. We focused on gall wasps (Hymenoptera:Cynipidae), the second largest clade of gall inducers (~1,400 spp.), for which the developmental stages and organs responsible for gall development are unclear. We investigated the female metasomal anatomy of 69 gall-inducing and 29 non-gall-inducing species across each of the major lineages of Cynipoidea, to test relationships between this lifestyle and the relative size of secretory organs. We confirmed that the venom apparatus in gall-inducing species is greatly expanded, although gall-inducing lineages vary in the relative size of these glands. Among these gallers, we measured the largest venom gland apparatus relative to body size ever recorded in insects. Non-galling inquiline species are accompanied by a reduction of this apparatus. Comparative microscopic analysis of venom glands suggests varying venom gland content across the lineages. Some oak gallers also had enlarged accessory glands, a lipid-rich organ whose function remains unclear, and which has not been previously studied in relation to gall formation. Together, the massive expansion of secretory organs specifically in gall-inducing species suggests a role of these secretions in the process of gall formation, and the variance in size of venom glands, accessory glands, and the contents of these glands among gallers, suggests that gall formation across this clade is likely to employ a diversity of molecular strategies.

Host–enemy interactions provide limited biotic resistance for a range‐expanding species via reduced apparent competition

AbstractAimAs species' ranges shift poleward in response to anthropogenic change, they may lose antagonistic interactions if they move into less diverse communities, fail to interact with novel populations or species effectively, or if ancestral interacting populations or species fail to shift synchronously. We leveraged a poleward range expansion in a tractable insect host–enemy community to uncover mechanisms by which altered antagonistic interactions between native and recipient communities contributed to ‘high niche opportunities’ (limited biotic resistance) for a range‐expanding insect.LocationNorth America, Pacific Northwest.MethodsWe created quantitative insect host–enemy interaction networks by sampling oak gall wasps on 400 trees of a dominant oak species in the native and expanded range of a range‐expanding gall wasp species. We compared host–enemy network structure between regions. We measured traits (phenology, morphology) of galls and interacting parasitoids, predicting greater trait divergence in the expanded range. We measured function relating to host control and explored if altered interactions and traits contributed to reduced function, or biotic resistance.ResultsInteraction networks had fewer species in the expanded range and lower complementarity of parasitoid assemblages among host species. While networks were more generalized, interactions with the range‐expanding species were more specialized in the expanded range. Specialist enemies effectively tracked the range‐expanding host, and there was reduced apparent competition with co‐occurring hosts by shared generalist enemies. Phenological divergence of enemy assemblages interacting with the range‐expanding and co‐occurring hosts was greater in the expanded range, potentially contributing to weak apparent competition. Biotic resistance was lower in the expanded range, where fewer parasitoids emerged from galls of the range‐expanding host.Main ConclusionsChanges in interactions with generalist enemies created high niche opportunities, and limited biotic resistance, suggesting weak apparent competition may be a mechanism of enemy release for range‐expanding insects embedded within generalist enemy networks.

Systemic insecticides for control of stem gall wasp in highbush blueberry.

The gall wasp, Hemadas nubilipennis Ashmead, is a pest of highbush and lowbush blueberry and can pose a challenge to control with foliar sprays due to adult activity being during bloom and because larval development is within plant tissues. We hypothesized that systemic insecticides that move within the blueberry vascular system would reach areas where H. nubilipennis eggs are laid, causing larval mortality. Three application methods, crown injection, soil drench, and foliar spray were applied to potted 'Jersey' blueberry bushes at 50% and 100% rates to quantify systemic residue concentrations in shoots and leaves. Additionally, systemic insecticides were evaluated for control of gall wasps using single-shoot bioassays and measuring larval mortality at 0.01%, 0.1%, 1%, and 10% of field rate provided within a floral pick. Systemic insecticides tested in both studies included imidacloprid, flupyradifurone, and spirotetramat. The potted bush residue study determined that insecticides moved from three tested sites of entry: the roots, crown cavity, and foliage. Results from the shoot bioassays found that the mean percent larval survival of H. nubilipennis was negatively correlated with the concentration of AI detected in galls. Imidacloprid and spirotetramat were found to have the greatest potential for control of H. nubilipennis due to mortality in the shoot bioassays and similar residue concentrations in the potted bush studies to shoot bioassays. Future research should evaluate systemic insecticides applied in highbush blueberry plantings for control of H. nubilipennis using the bioassay mortality assessment method developed in this study.

Phytochemical Analysis, Antioxidant and Enzyme-Inhibitory Activities, and Multivariate Analysis of Insect Gall Extracts of Picea koraiensis Nakai.

Picea koraiensis Nakai (PK) is an evergreen tree. It plays an important role in landscaping and road greening. Insect galls of PK are formed by parasitism of the adelgid Adelges laricis. Except for phenolics, other chemical constituents and biological activity of insect gall from PK are still unknown. Thus, here, we performed phytochemical and biological activity analyses of PK insect gall extracts, aiming to turn waste into treasure and serve human health. PK insect gall extracts were prepared using seven solvents. Antioxidant activities of the extracts were examined via antioxidant assays (radical and oxidizing substance quenching, metal chelating, and reducing power). The inhibitory activities of the extracts were determined toward the key human-disease-related enzymes α-glucosidase, α-amylase, cholinesterase, tyrosinase, urease, and xanthine oxidase. The content of numerous active constituents was high in the methanol and ethanol extracts of PK insect gall, and these extracts had the highest antioxidant and enzyme-inhibitory activities. They also showed excellent stability and low toxicity. These extracts have potential for use as stabilizers of olive and sunflower seed oils.

Galling insect communities mediate the effects of fire on their associated parasitoid communities

Abstract Understanding fire effects on multitrophic levels is critical to the context of changes in fire regime and climate. Insects located at higher trophic levels, like parasitoids, are more vulnerable to habitat changes than insect herbivores because they need well‐established populations of their hosts to survive. Currently, fire effects on parasitoids and their interactions with their hosts are unknown. Our aim was to study the changes in abundance, richness and species composition, as well as the food web structure in a system involving parasitoids and galling insects under different fire scenarios. We asked whether potential changes in abundance, species richness and composition of parasitoid communities are explained by galled plant abundance, species richness and composition of galling insects, and how fire affects the structure of galling insect–parasitoid food webs. The highest parasitoid richness was found in the 9 years after fire scenario, whereas parasitoid abundance was not affected by fire. The parasitoid species composition in the 9 years after fire scenario was different from that in the unburned and 3 years after fire scenarios. Parasitoid communities were modulated by galled plant abundance, species richness and composition of galling insect communities. Vulnerability was significantly higher in 9 years after fire scenarios, but it increased with increasing network size. Fire affects the community of parasitoids through changes in their host communities. Differences in exclusivity to fire scenarios and diet specialisation of parasitoid species and galling insect richness may explain the patterns found. Our study supports evidence that fire creates habitats heterogeneous in the availability of hosts shaping the parasitoid communities, with a bottom‐up effect in food webs. Additionally, in burned areas were recorded unique galling insect–parasitoid interactions.

Torymus sinensis and its close relatives in Europe: a multilocus phylogeny, detailed morphological analysis, and identification key

The introduction of the biological control agent Torymus sinensis Kamijo (Hymenoptera, Chalcidoidea, Torymidae) to control the populations of the chestnut gall wasp Dryocosmus kuriphilus Yasumatsu (Hymenoptera, Cynipidae) is considered one of the successful programs in biological control. The species was involved in interspecific hybridisation in Japan and the specimens imported into Europe were derived from this hybrid lineage, showing signs of introgression. The discovery of mitochondrial haplotypes or possible Enolase haplotypes from T. beneficus or of specimens with shorter ovipositor does not necessarily imply that T. beneficus is present in Europe, only that the European specimens are of hybrid origin. Of the native European Torymus species associated with D. kuriphilus, the molecular and morphometric results indicate Torymus notatus (Walker) as the closest species to T. sinensis. The two are part of the same species-group (cyaneus group), are nested together in the multivariate ratio analysis and are the closest genetically based on all three nuclear markers: Enolase (1.5% divergence), Wingless (2%) and ITS2 (13%). However, on the mitochondrial marker COI the closest species is Torymus rubi (Schrank) at 9.9% divergence. As such, T. notatus is the most likely candidate for accidental interspecific hybridisation if this is to happen in Europe. We provide an illustrated identification key for the European species of Torymus associated with D. kuriphilus, an important but lacking tool for biological control programs.

Diversity of Foliar Gall Insects and Its Associated Host Plants from the Eastern Himalayan Foothills, India

Diversity of Foliar Gall Insects and Its Associated Host Plants from the Eastern Himalayan Foothills, India

First record of parasitoids Megastigmus sp. and Quadrastichus mendeli as potential biological control agents of eucalyptus gall inducers in Tanzania

Leptocybe invasa and Ophelimus maskelli (Hymenoptera: Eulophidae) are serious pests causing damage to eucalypt plantations in Tanzania. Biological control is considered the best alternative to other control methods, both ecologically and economically. Thus far, no parasitoid of the eucalyptus gall wasps documented or reported. Likewise, the number of parasitoid species and their parasitic capacities are unknown. Therefore, the study investigated the parasitoids of the eucalypt gall inducer from October 2021 to April 2022. Galls were collected from E. tereticornis and E. grandis x E. camaldulensis clones and reared until wasps emerged. The emerged wasps were sorted and identified at the Sokoine University of Agriculture, Tanzania, and the Insect Biosystematics Laboratory at IPB University, Indonesia. Two species of parasitoids of eucalyptus gall-inducers in Tanzania were first collected and identified as Megastigmus sp. (Torymidae) and Quadrastichus mendeli (Eulophidae). In Korogwe, North Ruvu, and Morogoro plantation areas, the percentages of parasitization for the two parasitoids combined were 29.7%, 64%, and 33.3%, respectively. A higher parasitization rate was observed from L. invasa galls in the E. grandis x E. camaldulensis clones. These parasitoids can be potential biological control agent candidates to control the pest. However, future monitoring is needed to determine their distribution, host specificity, interactions, and efficacy.

Morphophysiological Responses in Eucalyptus Demonstrate the Potential of the Entomopathogenic Fungus Beauveria bassiana to Promote Resistance against the Galling Wasp Leptocybe invasa

The galling insect Leptocybe invasa Fisher & La Salle (Hymenoptera: Eulophidae) is a major limiting factor in the cultivation of drought-tolerant eucalyptus. The insect L. invasa is a major pest of eucalyptus plantations, and Beauveria bassiana (Bals.) Vuill (Ascomycota: Hypocreales) is being investigated as a potential biocontrol agent against this pest. The fungus B. bassiana can produce metabolites that affect insect biology and survival. Here, we investigated the ability of the entomopathogenic B. bassiana to endophytically develop and induce resistance to L. invasa in a drought-tolerant eucalyptus hybrid. In a greenhouse under semi-controlled conditions, a group of seedlings were sprayed with a solution containing the fungal spores of B. bassiana. The uninoculated seedlings and seedlings inoculated were infested with L. invasa, and their morphometric responses, gas exchange, and chlorophyll indexes were assessed. The number of leaves and height of the inoculated plants was higher than those of the uninoculated plants. The mean CO2 assimilation rate (A) and transpiration rate (E) were higher for inoculated plants. The inoculated plants showed higher chl a and chl b contents. Compared to the uninoculated plants, the inoculated plants developed much fewer galls, while some showed only scar formations where L. invasa deposited its eggs. These results indicated that inoculating Eucalyptus with B. bassiana promoted resistance to L. invasa. To the best of our knowledge, this is the first study showing that an entomopathogenic fungus can develop endophytically to promote resistance against a galling insect pest.

Molecular Aspects of Gall Formation Induced by Mites and Insects.

Recent publications on gall formation induced on the leaves of dicotyledonous flowering plants by eriophyoid mites (Eriophyoidea) and representatives of four insect orders (Diptera, Hemiptera, Hymenoptera, Lepidoptera) are analyzed. Cellular and molecular level data on the stimuli that induce and sustain the development of both mite and insect galls, the expression of host plant genes during gallogenesis, and the effects of these galling arthropods on photosynthesis are considered. A hypothesis is proposed for the relationship between the size of galls and the volume of secretions injected by a parasite. Multistep, varying patterns of plant gene expression and accompanying histo-morphological changes in the transformed gall tissues are apparent. The main obstacle to better elucidating the nature of the induction of gallogenesis is the impossibility of collecting a sufficient amount of saliva for analysis, which is especially important in the case of microscopic eriophyoids. The use of modern omics technologies at the organismal level has revealed a spectrum of genetic mechanisms of gall formation at the molecular level but has not yet answered the questions regarding the nature of gall-inducing agents and the features of events occurring in plant cells at the very beginning of gall growth.

Cynipidae (Hymenoptera, Cynipoidea) fauna of Burdur province (Türkiye).

Field studies were conducted between September 2020 and June 2022 to assess the gall wasp (Hymenoptera: Cynipidae) fauna of Burdur province (Southwestern Türkiye). A total of 69 species in 18 genera were recorded. Gall samples were collected from 150 samples collected in 100 different localities in the surveyed area. The identified species include three new records (Andricus melikai Pujade-Villar & Kwast, 2002; A. pseudocecconii Melika, Tavakoli & Stone, 2022; Saphonecrus undulatus (Мауr, 1872)) for the Turkish cynipid fauna. As a result of this study, 44 species of the current Turkish cynipid fauna were recorded from Burdur province for the first time. A checklist of the species and their host plants and/or host galls recorded in the study area is provided. The gall wasp richness and geomorphic-topographic structure of Burdur province is discussed.

Influence of the sex of galling insects on gall metabolism: The case of eriococcid galls

Eriococcidae-induced galls may accumulate all sorts of primary and secondary plant metabolites, but as phloem suckers, such accumulation is commonly related to the maintenance of gall structure rather than to the galling insect nutrition. For galling Eriococcidae, the feeding activity of female and male insects may have different impact on the metabolic profile of the galls. Accordingly, even under the stimuli imposed by the same species, the morphological peculiarities of Eriococcidae galls are related to sexual dimorphism. The dimorphism has been explained by the differences in their lifespans, herein examined in Annona dolabripetala (Annonaceae)- Pseudotectococcus rolliniae (Eriococcidae) and Pseudobombax grandiflorum (Malvaceae)- Eriogallococcus isaias (Eriococcidae) systems. We assume that the galls induced by females with their longer life cycles generate a higher demand for metabolites than the galls induced by males, and check it out by analyzing the histochemical and anatomical profiles of the galls. The primary metabolites, starch, and lipids, accumulate only in the inner cortex of the female-induced galls of both species and may work out in the dissipation of reactive oxygen species (ROS), as the accumulation of these primary metabolites may consume ROS. Regarding the secondary metabolites, terpenoids accumulate in the inner and median cortices of the male-induced galls of the two host species. In the female-induced galls, secondary metabolites accumulate in the outer cortex where they can be related to the sexual attraction of the males to copulate with the sessile females inside the gall chamber. The female-induced galls on A. dolabripetala e P. grandiflorum, with their longer life cycles, accumulate a wider histochemical profile, corroborating our hypothesis.

Identification Research of Trichagalma Glabrosa Insect Gall Pests Based on YOLOv5s

In order to solve the problem of low image identification accuracy of Trichagalma glabrosa insect gall pests in a complex natural environment, an image identification method of Trichagalma glabrosa insect gall pests based on YOLOv5s was designed and introduced in this study. The original images were preprocessed with the grayscale maximum method and different gradients of noise, which reduced the color difference interference with complex backgrounds and improved the image identification rate. A total of 6090 images of insect gall pests under opposite light, back light, and complex backgrounds were constructed, which were divided into a training set and a test set with a ratio of 7 : 3. The results showed that the precision, recall, and mean average precision of YOLOv5s were 94.35%, 95.42%, and 95.8%, respectively. YOLOv5s, YOLOv4, and Faster-RCNN were compared and analyzed under the same test conditions. The identification accuracy of YOLOv5s was higher than that of YOLOv4 and Faster-RCNN, and its model size was only 13.8 MB. It was considered that the designed YOLOv5s method could help accurately and quickly identify Trichagalma glabrosa insect gall pests with high identification accuracy and a small model capacity, which was more conducive to the migration application of the model, and provide a new method for the rapid identification of Trichagalma glabrosa insect gall pests in a complex natural environment.

Brown Rot Caused by Gnomoniopsis smithogilvyi (syn. Gnomoniopsis castaneae) at the Level of the Chestnut Tree (Castanea sativa Mill.)

The European chestnut tree (Castanea sativa Mill.) has great economic importance, mostly due to the recognized nutritional value of its fruit. Thus, the development and improvement of the techniques of the production, preservation, and control of the diseases/pests of chestnut trees is a topic of great interest to producers, companies, researchers, and consumers to ensure the quality of this exceptional fruit. Recently, an emerging rot in chestnuts caused by the fungus Gnomoniopsis smithogilvyi (syn. Gnomoniopsis castaneae Tamietti) (Gnomoniaceae, Diaporthales) was reported both in Australia and Europe. Since then, the number of records of this pathogen in several countries of the world (Europe and Asia) where Castanea spp. is cultivated has been increasing. This disease, called “brown rot”, has been causing significant production losses, raising serious concerns for producers and the chestnut industry. This review describes the world distribution and life cycle of the causal agent of brown rot. The life cycle of G. smithogilvyi can involve primary infection, caused by ascospores, and secondary infection, related to the asexual phase of the fungus (conidia). Then, the analytical methods used to detect G. smithogilvyi are described. Furthermore, the incidences of the disease caused by G. smithogilvyi are presented, ranging from 5 to 94%, with high infection rates causing significant economic losses. The damages caused by G. smithogilvyi are discussed. In fact, it can act as an endophyte or as a pathogenic fungus, causing fruit rot, canker in several plant tissues, and necrosis in leaves, as well as in galls caused by the gall wasp Dryocosmus kuriphilus Yasumatsu. Possible pre- and post-harvest methods to mitigate the damage caused by moulds, and in particular G. smithogilvyi, are presented, including biocontrol agents and chemicals. Finally, some challenges and future prospects for a number of uncertainties related to the epidemiology, geographic distribution, spread, detection, and management of this disease are discussed.

Leaf Trait Hyperspectral Characterization of Castanea sativa Miller Affected by Dryocosmus kuriphilus Yasumatsu

While populations of the Asian chestnut gall wasp (Dryocosmus kuriphilus Yasumatsu), an invasive pest affecting the European chestnut (Castanea sativa Miller), have started to be controlled biologically, this pest still conditions chestnut tree development. With the aim of assessing plant health status as a means of monitoring gall wasp infestation, we used a field spectroradiometer to collect data from leaves taken from 83 trees in two chestnut orchards. We calculated characteristic spectral signatures for pest infestation, and after training and validation, developed classifiers to distinguish between different infestation levels. Several partial least square discriminant analysis (PLS-DA) and random forest (RF) models were fitted with reflectance and transformed values to obtain characteristic curves reflecting infestation. Four wavelengths (560 nm, 680 nm, 1400 nm, and 1935 nm) were identified as showing the greatest differences between curves. The best overall accuracy (69.23%) was achieved by an RF model fitted with reflectance transformed values. Lower overall accuracy (26.92%) was achieved in distinguishing between infestation levels. In conclusion, while more specific differences in infestation levels were not detectable, our method successfully discriminated between gall absence and presence.

The role of Anatolia between Asia and Europe: A case study of oak gall wasp species, Cynips quercus (Hymenoptera, Cynipidae)

In this study, we used DNA sequence data of a western Palearctic oak gall wasp species, Cynips quercus, showing distribution from Europe to Iran to answer the following questions: i) Do the eastern C. quercus populations have higher genetic diversity than the European populations?, ii) Are the eastern populations source for the European populations?, iii) What is the possible date of divergence between the Asian and European populations? For these purposes, we analysed 88 cytochrome b sequences representing Iran, Türkiye, Hungary, and Spain. Our analyses revealed that the highest genetic diversity was in Türkiye followed by Iran, Hungary, and Spain, respectively. Iranian samples were most divergent from the Spain and Hungary sequences. Pairwise comparisons showed that the highest gene flow was between Türkiye and Hungary, and between Türkiye and Iran, respectively. Phylogenetic analysis grouped the Turkish haplotypes with the Iranian sequences, and Spain was grouped with Hungary. Network analysis revealed that the western Turkish samples were separated from eastern sequences, and all of the eastern Turkish sequences were clustered with the Iranian samples meanwhile a western Turkish lineage provided a source to Hungary and then to Spain. Times of divergence analysis estimated that the Turkish lineage split from the Iranian lineage around 4,67 million years ago, and Hungarian and Spanish lineages diverged from each other about 3 million years ago. Correspondingly, our analyses suggested that Anatolia played a key role as a bridge between the Asian and European populations of C. quercus.

First Record of the Eucalyptus Gall Wasp, Ophelimus maskelli (Ashmead) in Nineveh Governorate, Iraq

Al-Jalal, H.M.M. and W.A. Yahya. 2023. First Record of the Eucalyptus Gall Wasp, Ophelimus maskelli (Ashmead) in Nineveh Governorate, Iraq. Arab Journal of Plant Protection, 41(1): 12-14. https://doi.org/10.22268/AJPP-41.1.012014 Gall wasps ophelimus maskelli were detected for the first time in Nineveh Governorate on the foliage of Eucalyptus tree during June, 2021. Symptoms of infestation were in the form of pus-like swellings on the fresh stems and leaf blade. Leaves of Eucalyptus camaldulensis were heavily infested with the gall wasp, with leaves infestation rate and severity of infestation reached 42.2% and 5.2 galls/cm², respectively. The results showed that the severity of infestation at the basal and middle leaves was higher than the terminal leaves, and the averages reached 5.38, 2.73 and 1.70 galls/cm², respectively. Keywords: Swelling wasp, Eucalyptus, rate of infestation, severity of infestation.

Assessing the susceptibility levels of chestnut cultivars/genotypes to Asian chestnut gall wasp (Dryocosmus kuriphilus Yasumatsu)

The Asian chestnut gall wasp Dryocosmus kuriphilus is a major insect pest affecting chestnut trees worldwide. Due to the galls that it creates on shoots and leaves, this pest prevents shoot development and blooming and decreases the fruit yield. In Türkiye, this pest was first seen in Gacık village of Yalova province in the year 2014. Today, it is seen in orchards and forests in different provinces of Marmara, Aegean, and Black Sea regions. The medium- and long-term control of this pest can be improved by making use of resistant or less-susceptible cultivars and hybrid clones. The susceptibility levels of our cultivars to this pest are not known. For this purpose, by using three infestation indicators, the susceptibility to Asian chestnut gall wasp (ACGW) of 3 hybrids (Castanea sativa x Castanea crenate) and 20 cultivars/genotypes (C. sativa), which came to the forefront via selection studies, were assessed for five years (2017-2021). The susceptibility to ACGW varied between the tested genotypes/cultivars and, since no gall development was observed in ‘YD-1’, ‘Tülü’, and ‘Ertan’ cultivars of C. sativa species, they were determined to be completely resistant to ACGW. Furthermore, the numbers of ACGW eggs on the buds of cultivars were recorded and it was found that ACGW laid eggs on the buds of all the cultivars. In microscopic analyses, it was revealed that the resistance originated from the prevention of larva development within the bud. The finding that resistant cultivars belong to C. sativa species is thought to be important for future genetic breeding programs.

Ab-GALFA, A bioassay for insect gall formation using the model plant Arabidopsis thaliana

Insect galls are abnormal plant organs formed by gall-inducing insects to provide shelter and nutrients for themselves. Although insect galls are spatialized complex structures with unique shapes and functions, the molecular mechanism of the gall formation and the screening system for the gall inducing effectors remains unknown. Here, we demonstrate that an extract of a gall-inducing aphid, Schlechtendalia chinensis, induces an abnormal structure in the root-tip region of Arabidopsis seedlings. The abnormal structure is composed of stem-like cells, vascular, and protective tissues, as observed in typical insect galls. Furthermore, we confirm similarities in the gene expression profiles between the aphid-treated seedlings and the early developmental stages of Rhus javanica galls formed by S. chinensis. Based on the results, we propose a model system for analyzing the molecular mechanisms of gall formation: the Arabidopsis-based Gall-Forming Assay (Ab-GALFA). Ab-GALFA could be used not only as a model to elucidate the mechanisms underlying gall formation, but also as a bioassay system to isolate insect effector molecules of gall-induction.

Torymus sinensis against the invasive chestnut gall wasp: Evaluating the physiological host range and hybridization risks of a classical biological control agent

BackgroundA common strategy to limit the negative impact of biological invasions is biological control through the release of specialized alien natural enemies. However, biological control plans are not without risks, which include parasitism of native hosts and hybridization with related native species, particularly those that are potential natural enemies of the invasive species. Here, we evaluate these potential risks resulting from the introduction of the parasitoid wasp Torymus sinensis (Hymenoptera: Torymidae) in Europe to control the invasive Asian chestnut gall wasp Dryocosmus kuriphilus (Hymenoptera: Cynipidae). ResultsWe found that, under laboratory conditions, the physiological host range of T. sinensis includes several native non-target species of Cynipidae, with oviposition observed on the galls of 8 of the 11 species tested. However, physiological host range of T. sinensis appears to be limited under field conditions, as we observed only one parasitized gall of Andricus curvator in the field. Regarding hybridization, inter-species mating between T. sinensis and its phylogenetically closest native Torymus species was not observed in the laboratory. Moreover, discordance between nuclear (ITS2) and mitochondrial (coxI) data does not support the presence of genetic introgression, suggesting that hybridization between T. sinensis and native Torymus species does not occur. In addition, we cite and discuss the unexpected presence of one individual of the related alien species Torymus beneficus in Spain. ConclusionOur results suggest that T. sinensis may negatively impact several non-target species, highlighting the need for careful monitoring of the extent of such undesired behaviour and its effects on the native fauna.