The Diversity of Bacteria Associated with the Invasive Gall Wasp Dryocosmus kuriphilus, Its Galls and a Specialist Parasitoid on Chestnuts

Dryocosmus kuriphilus (Hymenoptera: Cynipidae) induces galls on chestnut trees, which results in massive yield losses worldwide. Torymus sinensis (Hymenoptera: Torymidae) is a host-specific parasitoid that phenologically synchronizes with D. kuriphilus. Bacteria play important roles in the life cycle of galling insects. The aim of this research is to investigate the bacterial communities and predominant bacteria of D. kuriphilus, T. sinensis, D. kuriphilus galls and the galled twigs of Castanea mollissima. We sequenced the V5–V7 region of the bacterial 16S ribosomal RNA in D. kuriphilus, T. sinensis, D. kuriphilus galls and galled twigs using high-throughput sequencing for the first time. We provide the first evidence that D. kuriphilus shares most bacterial species with T. sinensis, D. kuriphilus galls and galled twigs. The predominant bacteria of D. kuriphilus are Serratia sp. and Pseudomonas sp. Furthermore, the bacterial community structures of D. kuriphilus and T. sinensis clearly differ from those of the other groups. Many species of the Serratia and Pseudomonas genera are plant pathogenic bacteria, and we suggest that D. kuriphilus may be a potential vector of plant pathogens. Furthermore, a total of 111 bacteria are common to D. kuriphilus adults, T. sinensis, D. kuriphilus galls and galled twigs, and we suggest that the bacteria may transmit horizontally among D. kuriphilus, T. sinensis, D. kuriphilus galls and galled twigs on the basis of their ecological associations.

Biological control of the Asian chestnut gall wasp in Portugal: Insights from a mathematical model

In recent years, the Asian gall wasp Dryocosmus kuriphilus has invaded chestnut trees and significantly affected the Portuguese chestnut production. Studies in other countries, such as Japan or Italy, have shown that the parasitoid Torymus sinensis can successfully achieve biological control of D. kuriphilus. Mathematical models help us to understand the dynamics of the interaction between the pest D. kuriphilus and its parasitoid T. sinensis and, consequently, they can help to implement measures that enhance crop pest management. In this work, the evolution of the density of D. kuriphilus and T. sinensis across time and space is studied through the numerical solution of models that include parameters based on observations made in Portugal. Simultaneous releases of the parasitoid are simulated at various locations and at different times. The results indicate that, in the case of a small and homogeneous orchard, biological control can be effective, but, in the case of extensive domains, the pest control is much more difficult to achieve. In order for biological control to be efficient, it is necessary to implement, in each chestnut-producing region, a collective strategy based on the annual monitoring of infestation levels.

An integrated transcriptomic and proteomic approach to identify the main Torymus sinensis venom components

During oviposition, ectoparasitoid wasps not only inject their eggs but also a complex mixture of proteins and peptides (venom) in order to regulate the host physiology to benefit their progeny. Although several endoparasitoid venom proteins have been identified, little is known about the components of ectoparasitoid venom. To characterize the protein composition of Torymus sinensis Kamijo (Hymenoptera: Torymidae) venom, we used an integrated transcriptomic and proteomic approach and identified 143 venom proteins. Moreover, focusing on venom gland transcriptome, we selected additional 52 transcripts encoding putative venom proteins. As in other parasitoid venoms, hydrolases, including proteases, phosphatases, esterases, and nucleases, constitute the most abundant families in T. sinensis venom, followed by protease inhibitors. These proteins are potentially involved in the complex parasitic syndrome, with different effects on the immune system, physiological processes and development of the host, and contribute to provide nutrients to the parasitoid progeny. Although additional in vivo studies are needed, initial findings offer important information about venom factors and their putative host effects, which are essential to ensure the success of parasitism.

Differences in native and introduced chalcid parasitoid communities recruited by the invasive chestnut pest Dryocosmus kuriphilus in two Iberian territories

Dryocosmus kuriphilus (Hymenoptera: Cynipidae) is a global invasive gall wasp and a pest of chestnuts (Castanea spp.). A study of the Chalcidoidea parasitoid community of D. kuriphilus was undertaken over two years, from March 2017 to March 2019, at 15 sites in south and northwest Spain (Málaga and Galicia regions). More than 18,000 galls were collected, and 1153 parasitoids belonging to 22 species of seven chalcidoid families, plus two individuals of an inquiline Cynipidae, Synergus facialis, emerged. Richness was higher in the Málaga region, with 20 species, while 17 parasitoids and one inquiline were identified in Galicia. The parasitism rate of native chalcid parasitoid species in both regions was low. Eupelmus urozonus and Mesopolobus lichtensteini were the most abundant native species. Mesopolobus tibialis was a dominant species in south Spain, while Ormyrus pomaceus was a dominant species in northwest Spain. Our results revealed the existence of a sub-community of univoltine, probably host specialized, parasitoids in south Spain, which overwinter in galls, exhibiting a similar life cycle to Torymus sinensis. These species were Torymus notatus, Aulogymnus bicolor, Aulogymnus obscuripes and Aulogymnus balani. Data on the recovery of T. sinensis after release in the south Spain region show it to be well established, but its numbers are still low in northwest Spain.

Newly invaded territories by Dryocosmus kuriphilus in Spain and first records of Torymus sinensis in the Sistema Central

Aim of the study: To update the distribution of Dryocosmus kuriphilus, the Asian chestnut gall wasp, focusing on the central area of the country (Sistema Central). Gall samplings of these areas were carried to obtain the first records of parasitoids on D. kuriphilus in this area.Area of study: Spain and, especially, the Sistema Central.Materials and methods: Georeferenced new records were used to produce a map with the updated distribution of D. kuriphilus as of 2019. Galls were collected and stored in emergence boxes. Parasitoids that emerge from these galls were collected and identified at the most detailed taxonomic level.Main results: The alien species D. kuriphilus was found in the Spanish Sistema Central. Infestation focal points were detected in the Valle del Jerte (South of Sierra de Gredos), Sierra de Francia and in the mountains southwest of Madrid. In all detected focal points of infestation, the available evidence indicates that introduction was caused by the accidental mobilization of infested chestnut material. Alongside other parasitoids recruited by D. kuriphilus, we found individuals of Torymus sinensis, constituting the first records of this foreign species in the Sistema Central.Research highlights: We updated the previously published distribution of D. kuriphilus in Spain, an alien species and pest of chestnut forests and orchards. We also reported the first list of recruited parasitoids by D. kuriphilus and, more specifically, the first records of T. sinensis in the Sistema Central.Keywords: Asian chestnut gall wasp; Torymus sinensis; parasitoids; galls; Iberian Peninsula; pest species; alien species.

Recruitment of native parasitoids by an introduced gall wasp Dryocosmus kuriphilus Yasumatsu, 1951 (Hymenoptera: Cynipidae) in Britain and France

The invasive chestnut gall wasp Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae) is a major pest species of Castanea spp. worldwide. It only arrived in Britain in 2015 and the parasitoid community associated with it was studied in 2019. Eight native species of chalcidoid, previously known to be associated with oak gall wasps, were identified. These results are compared to a similar study (2016–2019) in France where four parasitoids were reared. However, this community included the deliberately introduced Torymus sinensis Kamijo, a specific biological control agent of D. kuriphilus. The presence of T. sinensis and the differences between the two communities is discussed.

The open bar is closed: restructuration of a native parasitoid community following successful control of an invasive pest

The rise of the Asian chestnut gall wasp Dryocosmus kuriphilus in France has benefited the native community of parasitoids originally associated with oak gall wasps by becoming an additional trophic subsidy and therefore perturbing population dynamics of local parasitoids. However, the successful biological control of this pest has then led to significant decreases in its population densities. Here we investigate how the invasion of the Asian chestnut gall wasp Dryocosmus kuriphilus in France and its subsequent control by the exotic parasitoid Torymus sinensis has impacted the local community of native parasitoids.We explored 5 years of native community dynamics within 26 locations during the rise and fall of the invasive pest. In an attempt to understand how mechanisms such as local extinction or competition come into play, we analyzed how the patterns of co-occurrence between the different native parasitoid species changed through time.Our results demonstrate that native parasitoid communities experienced increased competition as the D. kuriphilus levels of infestation decreased. During the last year of the survey, two alternative patterns were observed depending on the sampled location: either native parasitoid communities were represented by an extremely limited number of species occurring at low densities, in some cases no native parasitoid species at all, or they were dominated by one main parasitoid: Mesopolobus sericeus. These two patterns seemed to correlate with the habitat type, M. sericeus being more abundant in semi-natural habitats compared to agricultural lands, the former known to be natural reservoirs for native parasitoids. These results highlight how the “boom-and-bust” dynamics of an invasive pest followed by successful biological control can deeply alter the structure of native communities of natural enemies.This article has been peer-reviewed and recommended by Peer Community in Zoologyhttps://doi.org/10.24072/pci.zool.100004