Chestnut Gall Wasp Dryocosmus Kuriphilus Research Articles

Interaction between Torymus sinensis (Hymenoptera: Torymidae) and T. beneficus, Introduced and Indigenous Parasitoids of the Chestnut Gall Wasp Dryocosmus kuriphilus (Hymenoptera: Cynipidae)

Torymus sinensis is a parasitoid wasp that was introduced from China to Japan to control the invasive chestnut gall wasp Dryocosmus kuriphilus. Interaction between T. sinensis and the indigenous parasitoid T. beneficus has been of interest since T. sinensis was first released in chestnut orchards, as hybridization between them might impede the success of biological control by the introduced parasitoid. Such apprehensions disappeared with the drastic decrease in damage caused by D. kuriphilus. However, the emergence of morphologically intermediate individuals between them after the introduction of the parasitoid has triggered renewed interest in hybridization, specifically on the non-target effects of biological control. In this review, the interaction between both species, specifically hybridization, species composition and species displacement, is surveyed. Molecular markers are used, not only because T. sinensis and T. beneficus are similar morphologically, but also because the latter has two emergence strains (early- and late-spring). Surveys show that 1) T. sinensis has displaced both emergence strains of T. beneficus; 2) hybridization between T. sinensis and early-spring T. beneficus occurs at a low frequency (≤ 1%); but that 3), hybrid F 1 s between T. sinensis and late-spring T. beneficus occur at a much higher frequency (≤ 20%). A study of phylogenetic relationships indicates that the late-spring T. beneficus is closer to the different species T. sinensis than the early-spring T. beneficus. This can partly explain why T. sinensis hybridizes more readily with the late-spring T. beneficus than with the early-spring T. beneficus.

Invasion by the chestnut gall wasp in Italy causes significant yield loss inCastanea sativanut production

The Asian chestnut gall wasp Dryocosmus kuriphilus Yasumatsu (Hymenoptera Cynipidae) is an invasive species in chestnut forests and orchards in many parts of the world. 2 Nuts produced by the European chestnut (Castanea sativa Miller) are important in human food and culture, and as a component in food webs in forest ecosystems. 3 Severe infestations are reported to reduce nut yield, although precise data are lacking because of large natural year-to-year variability in yield. 4 The recent colonization of chestnut orchards in north-eastern Italy, where nut yield has been continuously and precisely recorded for several years, offered an opportunity to calculate the impact of gall wasp infestation level on yield. 5 The nut yield of C.sativa chestnut trees was negatively related to the gall wasp infestation level, with losses as high as 80% being reported when the number of current-year galls was above six galls per 50-cm twig. 6 Yield losses can be explained by direct and indirect factors related to gall formation, and a fuller understanding of the mechanisms involved could identify possible mitigation measures.

Chalcid parasitoid community associated with the invading pest Dryocosmus kuriphilus in north‐western Italy

Abstract. 1. Biological invasions of exotic species pose a major threat to native biodiversity. Invaders are known to have direct impacts on native species; however, less well studied are the indirect impacts mediated through the integration of invaders into trophically linked communities.2. A survey of the chalcid wasp parasitoid community attacking the chestnut gallwasp Dryocosmus kuriphilus was carried out over a 5‐year period at 26 sites in north‐western Italy. More than 415 000 galls were collected and more than 10 000 parasitoid specimens emerged. Twenty‐seven parasitoid species belonging to six families (Eurytomidae, Pteromalidae, Torymidae, Eupelmidae, Ormyridae, Eulophidae) were identified using morphological and molecular methods; seventeen are new records for the parasitoid community associated with D. kuriphilus in Italy. The morphospecies complexes Megastigmus dorsalis, Eupelmus urozonus, E. annulatus, and Eurytoma pistaciae were the dominant species; another six morphospecies were encountered regularly but at low frequency; and 13 species were recorded only occasionally. The attack rate of any individual parasitoid species was low, although the more common species appeared to be increasing their use of this novel host.3. Biases observed in the sex ratios of parasitoids emerging from D. kuriphilus galls suggest that parasitoid individuals are making life‐history decisions to take advantage of the high abundance of this host. Overall, these patterns imply that there is an ongoing transfer of parasitoids between oak and chestnut galls, and hence a high potential for this invading species to have a major impact on native oak gall communities via indirect competition mediated through shared parasitoids.

Influence of the introduced parasitoid Torymus sinensis (Hymenoptera: Torymidae) on T. koreanus and T. beneficus as indigenous parasitoids of the chestnut gall wasp Dryocosmus kuriphilus (Hymenoptera: Cynipidae) on chestnut trees in Nagano Prefecture, Japan

We describe here the parasitoid wasps Torymus sinensis Kamijo and T. beneficus Yasumatsu & Kamijo (early-spring and late-spring strains), which are introduced and indigenous natural enemies of the chestnut gall wasp Dryocosmus kuriphilus Yasumatsu, an invasive chestnut pest in Japan. We recently discovered specimens of T. koreanus Kamijo, endemic in Korea, among Torymus parasitoids collected from D. kuriphilus galls in a Japanese chestnut orchard. In this study we compare the composition of Torymus parasitoids emerging from D. kuriphilus galls before and after the release of T. sinensis. Before the release of T. sinensis, early-spring and late-spring strains of T. beneficus predominated (58.3 and 20.8% of specimens collected). However, a few years after the release, both T. beneficus strains had been almost completely displaced by T. sinensis. In contrast to the rapid decrease in T. beneficus, T. koreanus did not decrease drastically before and even after the release of T. sinensis (approximately 10–20% of specimens collected). These results suggest that not a few T. koreanus were present in the Japanese chestnut orchard investigated at least several years after the release of T. sinensis, although both the T. beneficus strains were rapidly displaced by T. sinensis during this period.

Torymus sinensis: a viable management option for the biological control of Dryocosmus kuriphilus in Europe?

The chestnut gall wasp Dryocosmus kuriphilus is a global pest of chestnut (Castanea spp). Established as a pest in the mid-twentieth century in Japan, Korea and North America, this species was first reported in Europe in 2002. Following the successful release of a biological control agent Torymus sinensis in Japan, this parasitoid species has been released in Italy since 2005. Here we discuss the potential of T. sinensis as a viable management option for the biological control of D. kuriphilus in central Europe. We suggest that more consideration should be given to determining, (i) the conditions under which T. sinensis may attack alternative native gall wasp hosts and (ii) the likelihood of hybridization of this species with native Torymus. Both issues are central to predicting unassisted range expansion by released T. sinensis, and to assess the environmental risks associated with a more widespread release of this species in Europe.

Chestnut gall wasp (Dryocosmus kuriphilus) infestations: new opportunities for the chestnut blight fungus Cryphonectria parasitica?

The invasive chestnut gall wasp Dryocosmus kuriphilus (Cynipidae) is one of the most important insect pests on Castanea species worldwide (EPPO, 2005). In 2009, D. kuriphilus was found for the first time in southern Switzerland, most…

Gnomoniopsis associated with necrosis of leaves and chestnut galls induced by Dryocosmus kuriphilus

Chestnut (Castanea spp.) is a very important crop in the Monti Cimini area (Viterbo, Italy) which is seriously infested with the key pest, chestnut gall wasp Dryocosmus kuriphilus (Speranza et al., 2009). In May 2009 such seriously infested chestnut plants in the Monti Cimini area were found with necrotic leaves and galls. Lesions on leaves were irregular and variable in size, lemon green to amber in colour with green margins. Initially, galls were olive green then became dark brown. Inside the galls larvae of chestnut gall wasp were dead. Tissue from the edge of lesions was surface-sterilized using 1% sodium hypochlorite, rinsed in sterile distilled water and aseptically cut in 5–10 pieces not exceeding 5 × 5 mm, plated on potato dextrose agar (PDA) in Petri dishes containing an antibiotic solution (0·2% streptomycin sulphate) and incubated at 20 ± 3°C. Light brown fungal colonies were observed after 1 week close to the tissue and numerous orange slimy masses of conidia were observed on the culture surface. The colonies were regular in outline with a clear and thinner margin. Conidia were oval to oblong, sometimes slightly obovoid, straight or curved and measured 5·5–8·0 μm × 2·0–3·0 μm (mean = 6·8 × 2·5 μm, n = 210). The fungus was identified at Centraalbureau voor Schimmelcultures (CBS, Utrecht, The Netherlands) as an undescribed species from the genus Gnomoniopsis. Identification was based on both DNA sequencing (ribosomal ITS) and morphology (GenBank Accession Nos. EU254851, EU254854, EU254855). The pathogenicity of the fungus was tested in the Tuscia University experimental farm using freshly isolated cultures. Ten chestnut galls were inoculated, after slight pinprick injury, with an aqueous suspension containing 2 × 106 spores/mL and incubated in clean cheesecloth covered with Parafilm. Control-injured galls were sprayed with sterile distilled water and incubated in the same manner. Control plants did not show any disease symptoms 60 days after inoculation. In contrast, the fungus produced characteristic blight symptoms on 90% of the inoculated galls. Similar blight symptoms were observed on chestnut twigs inoculated with 4 mm discs of 7-day-old PDA cultures. Isolations from these lesions confirmed the presence of a fungus identical to Gnomoniopsis. Although chestnut leaf blight has been reported to be caused by some species of the genus Gnomonia (Sogonov et al., 2008), this appears to be the first record of a fungus in the genus Gnomoniopsis associated with the necrosis of chestnut galls caused by Dryocosmus kuriphilus. This Gnomoniopsis sp. has not been reported in Italy on non gall-infested leaves of chestnut trees (Cristinzio, 1986). The relationship between the necrotrophic propensity of Gnomoniopsis and chestnut gall wasp infestation is under investigation. The authors would like to thank the Regione Lazio (Italy) for financial support.

CHEMICAL CONTROL OF CHESTNUT WEEVILS IN CENTRAL ITALY

In Central Italy Chestnut Gall Wasp Dryocosmus kuriphilus Yasumatsu, Chestnut Weevils and two Chestnut Moths, Cydia fagiglandana (Zeller) and C. spendana (Hubner) are the key insect pests of chestnut orchards. In Latium Region two species of chestnut weevils, Curculio elephas (Gyll.) and C. propinquus (Desbr.), are represented at 5% and 95% respectively. These two carpophagous insects can generate severe yield losses, variable in the years from 20 to 90%. In order to minimize the rate of damaged chestnuts, chemical control trials were carried out comparing two active ingredients: Thiacloprid and Etofenprox. The results show a higher effectiveness of a.i. Thiacloprid with respect to Etofenprox and control treatments.

Hybridization between introduced Torymus sinensis (Hymenoptera: Torymidae) and indigenous T. beneficus (late-spring strain), parasitoids of the Asian chestnut gall wasp Dryocosmus kuriphilus (Hymenoptera: Cynipidae)

Hybridization between introduced biological control agents and native species is a nontarget effect of biological control. However, the genetic impacts related to introduced insects, especially from the viewpoint of post-release evaluation, remain largely unexplored. Torymus sinensis (Hymenoptera: Torymidae) is a parasitoid wasp introduced from China into Japan to control the invasive Asian chestnut gall wasp Dryocosmus kuriphilus (Hymenoptera: Cynipidae). After T. sinensis was first released in 1982, the damage caused by D. kuriphilus fell greatly. Previous studies showed that hybridization between T. sinensis and indigenous Torymus beneficus (the early-spring strain) was rare in the field, but individuals morphologically intermediate between T. sinensis and T. beneficus then appeared in the field. Here, we examined the frequency of hybridization between T. sinensis and the late-spring strain of T. beneficus by using the internal transcribed spacer 1 (ITS1) region of nuclear rDNA. Increasing numbers of F 1 hybrids were detected every year from 1993 to 1996, reaching 22%. It seems that T. sinensis can hybridize more easily with the late-spring strain of T. beneficus. Morphological indices of the F 1 hybrid type ranged between indices of the late-spring strain of T. beneficus and T. sinensis, with considerable overlap. Simultaneous with the occurrence of the F 1 hybrids, the indigenous late-spring strain of T. beneficus was rapidly displaced by T. sinensis.

DIFFERENTIAL GENE EXPRESSION IN CHESTNUT BUDS FOLLOWING INFESTATION BY GALL-WASP (DRYOCOSMUS KURIPHILUS YASUMATSU, HYMENOPTERA: CYNIPIDAE)

The chestnut gall-wasp Dryocosmus kuriphilus Yasumatsu, an insect native to China, was found in 2002 for the first time in Europe, and specifically in North western Italy (Cuneo province). The cynipid lays eggs into dormant buds and, in the following year, causes the development of galls on leaves, sprouts and inflorescences, due to the feeding activity of larvae. The wasp has an effect both on growth and yield of the tree. Complete resistance to D. kuriphilus was recently found in the hybrid Bouche de Betizac (C. sativa × C. crenata) and the genetic bases regulating this resistance are being investigated. Accessions of the cultivars Marrone (susceptible) and Bouche de Betizac (resistant) were subjected to an intensive attack of D. kuriphilus, with the purpose of getting infested buds to be examined at different stages of development of larvae. At budburst and just afterwards (March-April) buds were collected for the extraction and isolation of mRNA. cDNA was obtained by reverse transcription and analysed using the differential display technique. Two protocols, differing for the primer design, were applied and the results showed that 13 mer primers in combination with one-base anchored oligo-dT primers produced the best scorable profiles. Differentially expressed bands were cloned, sequenced and blasted with sequences deposited in NCBI and TIGR databases; putative genes were identified. The results showed that early activity of larvae in susceptible genotypes particularly influences the expression of genes involved in differentiation and nourishing; other genes found differentially expressed in infested tissues are involved in the plant response to external stimuli.

Rearing, release and settlement prospect in Italy of Torymus sinensis, the biological control agent of the chestnut gall wasp Dryocosmus kuriphilus

Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae), is one of the most serious pests attacking chestnut trees. Recently it was incidentally introduced into Northwest Italy and it is now spreading throughout Europe. This pest was successfully controlled in Japan by introducing a parasitoid, Torymus sinensis Kamijo (Hymenoptera: Torymidae), from China’s mainland. Following this successful experience, the parasitoid was introduced into Italy from Japan. One year of preliminary studies led to a successful method of rearing imported galls with a synchronization between the parasitoid’s emergence and the presence of the target galls in the field. In two consecutive years, a total of 2,117 individuals were released in several sites covering most of the infested area. There are encouraging data about the settlement of the parasitoid and its synchrony with the host’s cycle: from about 64,000 host galls collected in the field over 200 T. sinensis were reared. The role of native parasitoids associated with the chestnut gall pest in its Italian distribution range is also discussed.

Displacement of Torymus beneficus (Hymenoptera: Torymidae) by T. sinensis, an indigenous and introduced parasitoid of the chestnut gall wasp, Dryocosmus kuriphilus (Hymenoptera: Cynipidae), in Japanese chestnut fields: Possible involvement in hybridization

Abstract Although there is empirical knowledge to suggest the displacement of Torymus beneficus (Hymenoptera: Torymidae) by Torymus sinensis, an indigenous and introduced parasitoid of the chestnut gall wasp Dryocosmus kuriphilus (Hymenoptera: Cynipidae), respectively, in Japanese chestnut fields, the underlying mechanisms are unclear. In this study, the displacement of the early-spring strain of T. beneficus by T. sinensis was surveyed in a chestnut field for nine successive years (n = 418), using two molecular markers, the internal transcribed spacer 2 of nuclear rDNA (ITS2) and the mitochondrial cytochrome oxidase subunit I (COI). We also investigated whether or not hybridization between the parasitoids was involved as an important factor in the displacement. All individuals from 1993 to 1995 were of the early-spring strain of T. beneficus type for both ITS2 and COI. After 1996, individuals with the same types decreased and ones of the T. sinensis type for both ITS2 and COI increased. On the other hand, there was only one individual that had T. sinensis type for ITS2 and the early-spring strain of T. beneficus type for COI, suggesting that individuals are descendants of the F1 hybrid between the early-spring strain of T. beneficus females and T. sinensis males. These results indicate that hybridization between them was not closely related to displacement in the field. We have also found hybridization between T. sinensis and another type of T. beneficus: the late-spring strain; this is the first report to show their hybridization in chestnut fields.

Native and introduced parasitoids attacking the invasive chestnut gall wasp Dryocosmus kuriphilus

The globally invasive chestnut gall wasp Dryocosmus kuriphilus was recently reported in Italy and threatens European chestnut orchards and native forests. Of Chinese origin, this species has invaded Japan, Korea, the USA, Nepal and Europe and in each region it has been attacked by parasitoids exploiting oak gall wasps. Classical biological control using the parasitoid Torymus sinensis (Hymenoptera: Torymidae) successfully reduced infestation in Japan. Subsequent work in Japan and Korea showed this parasitoid to represent a poorly understood and biologically diverse species complex. Following its success in Japan, T. sinensis was released in Italy in 2005. A growing appreciation of the taxonomic and ecological complexity of the T. sinensis complex in Japan and Korea has stimulated ongoing DNA‐based work on relationships and interbreeding of species in this group. Oak cynipid parasitoids provide potential for native augmentative or conservation biological control of D. kuriphilus in Europe. Exploitation of this potential requires improved understanding of the taxonomy of these parasitoids, particularly of morphologically highly conserved lineages such as Eurytoma and Eupelmus in which recognised species may contain many cryptic lineages. There is a growing need for a molecular survey of the communities centered on chestnut and oak gall wasps to: (1) ascertain the identity of T. sinensis lineages released in Italy (2) track the dispersal of T. sinensis in the native community, either in its original form or as hybrids with native species (3) identify possible biological control agents in the native parasitoid community.

Identification of Torymus sinensis and T. beneficus (Hymenoptera: Torymidae), introduced and indigenous parasitoids of the chestnut gall wasp Dryocosmus kuriphilus (Hymenoptera: Cynipidae), using the ribosomal ITS2 region

Abstract The parasitoid wasps Torymus sinensis and T. beneficus (Hymenoptera: Torymidae) are introduced and indigenous natural enemies, respectively, of the chestnut gall wasp Dryocosmus kuriphilus (Hymenoptera: Cynipidae), an invasive pest of chestnuts in Japan. T. beneficus has two emergence types in spring, here tentatively designated as the early-spring strain and late-spring strain. It is very difficult to distinguish these two Torymus species accurately according to their morphological and ecological characteristics. Although the sequences of internal transcribed spacer 2 of the nuclear ribosomal DNA (ITS2) of these parasitoids are very similar, we have developed a pair of primers for amplifying a part of ITS2 that distinguishes species and emergence type. By performing high-resolution electrophoresis of PCR products amplified by this specific primer pair, we have succeeded in accurately identifying T. beneficus (early-spring strain) and some T. sinensis parasitoids. However, this technique was discovered to be inapplicable to identify other T. sinensis and T. beneficus (late-spring strain) parasitoids with the same ITS2 genotype. In spite of this problem, the ITS2 marker appears to be more powerful than any other molecular markers so far reported, since it is applicable to detection of T. beneficus, T. sinensis, and their hybrids.

Relationship between the introduced and indigenous parasitoids Torymus sinensis and T. beneficus (Hymenoptera: Torymidae) as inferred from mt-DNA (COI) sequences

The parasitoid wasps Torymus sinensis (Ts) and three strains of T. beneficus (early-spring strain: TbE; late-spring strain: TbL; autumn strain: TbA) are respectively introduced and indigenous natural enemies of the chestnut gall wasp Dryocosmus kuriphilus, an invasive chestnut pest. In this study, the genetic relationships among Ts and three strains of Tb from Japan, China and Korea were investigated by sequencing a portion of the mitochondrial cytochrome oxidase subunit I (COI) gene. Three distinct groups were recognized in a constructed phylogenetic tree, the first group further consists of three subgroups. Ts belongs to two subgroups, whereas TbL belongs to the remaining subgroup. TbE and TbA belong to the second group, indicating that TbL is genetically more closely related to Ts a different species than to TbE and TbA strains considered the same species. This requires a reconsideration, especially for TbL, of their taxonomical treatment. The third group consisted of an indigenous Torymus parasitoid that we were unable to identify morphologically, indicating that an unknown Torymus parasitoid that is both genetically and morphologically different from the Ts and the Tb strains exploits D. kuriphilus in Japan.

クリマモリオナガコバチとチュウゴクオナガコバチの羽化消長の比較

The adult emergence periods of the native Torymus (Syntomaspis) beneficus and the imported Chinese congeneric species, both parasitoids of the chestnut gall wasp Dryocosmus kuriphilus, were investigated in Fukuoka, 1980-1981. The appearance of 50 % females of the native beneficus is about 10 days earlier than gall appearance, therefore, many individuals which emerged early may die without ovipositing in the host galls. While, the Chinese species emerges after the appearance of the galls, so all the females can attack the host galls. Because of the better synchronized adult emergence, it is expected the Chinese Toryraaus (Syntonaaspis) sp. may be a more effective biological control agent than the Japanese beneficus.