Dryocosmus Kuriphilus Research Articles

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.

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.

No loss of genetic divergence in Torymus sinensis following its release for Dryocosmus kuriphilus control in Europe

Abstract Arrival, establishment, and further dispersal of non‐native natural enemies are considered essential for a successful biological control programme, while among the factors that may determine the success of such a programme, genetic diversity of the introduced population plays an important role in the establishment of a non‐native species. The Chinese parasitoid wasp Torymus sinensis Kamijo (Hymenoptera: Torymidae) was initially released in Europe in Italy to control biologically the Asian chestnut gall wasp Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae), and reduce the damage induced on sweet chestnut (Castanea sativa Miller). In the following years, T. sinensis was then released in numerous other European countries as a biological control agent of D. kuriphilus. Its presence has also been reported beyond the countries of release due to rapid natural dispersal. To assess the post‐release genetic diversity of D. kuriphilus, we screened T. sinensis populations from six European countries and tested the possibility of these populations suffering from frequently observed genetic effects that could threaten its successful establishment in Europe. Our results exhibit that T. sinensis populations have suffered neither from the Allee effect nor from genetic bottleneck after their release and establishment in Europe, something that increases the possibility to effectively control D. kuriphilus in Europe.

The impact of the Asian chestnut gall wasp (Dryocosmus kuriphilus) on chestnut tree growth may be mediated by site resources

IntroductionThe Asian chestnut gall wasp (Dryocosmus kuriphilus) is a major pest of chestnut trees worldwide, seriously affecting chestnut cultivation. Information concerning the effects of gall wasp attack on diameter growth of chestnut trees is currently scarce and limited to coppice stands and to use of the growth of a non-target control species (unaffected by the pest) for reference purposes. The effects of the pest on widely-spaced plantations (grown at a much lower density than chestnut coppices) and the use of explicitly-observed annual infestation rate data remain to be explored.MethodsIn the present study, we analyzed the impact of the chestnut gall wasp on the diameter growth of chestnut trees, using data from 16 experimental plots established in widely-spaced plantations located in good quality sites. Two of the plots are in plantations where a susceptible hybrid chestnut clone and a chestnut clone resistant to the gall wasp coexist, whereas the remaining 14 plots are in Castanea sativa plantations where the level of gall wasp infestation varies across trees and years. The plots were surveyed to determine the diameter growth of the trees and the level of infestation during 5 years (2017–2021).ResultsThe infestation level corresponding to the theoretical damage threshold was surpassed inmost plots during the study period. Nevertheless, there were no differences in the growth of attacked and unaffected plants in the two plots planted with hybrid clones with contrasting susceptibility to the gall wasp. The attack had a modest effect in C. sativa plots, with a mean reduction in annual basal area increment of 9.9%.DiscussionThese findings apparently contradict previous reports of a marked reduction in radial growth of chestnut coppice trees due to gall wasp attack. The difference in findings may be related to increased compensation for herbivory with increasing levels of resources (especially light) in the plantations under study, which were less dense than previously studied stands. The study outcomes add to existing knowledge on the impact of chestnut gall wasp on wood formation and may have implications regarding planting site recommendations and subsequent stand management.

DISCOVERY OF ALIEN INVADERS IN THE GALLS OF THE <i>DRYOCOSMUS KURIPHILUS</i> HALTWORK (HYMENOPTERA, CYNIPIDAE) IN THE NORTHERN CAUCASUS

The Eastern chestnut gall wasp, Dryocosmus kuriphilus Yasumatsu 1951, after having appeared in forests with the participation of the common chestnut in Russia, soon began to cause significant damage. The study of its biology revealed the presence of several insects in its galls, which use them as a new habitat. In fact, the use of galls by alien inhabitants of local chestnut consumers new to aboriginal forest communities has started. The role of these consumers for the eastern chestnut gall washer is currently unknown.

Damage ratio of the Asian chestnut gall wasp, Dryocosmus kuriphilus Yasumatsu, 1951 (Hemiptera: Cynipidae) in Samsun Province of Türkiye: First Report

The Asian chestnut gall wasp Dryocosmus kuriphilus Yasumatsu (Hymenoptera, Cynipidae) is a critical pest that threatens chestnut cultivation. The chestnut gall wasp causes yield losses by deforming the buds of the infected trees. This pest, which was first detected in Italy in 2002 in Europe, was seen in Gacık village of Yalova province in 2014 in Türkiye. In the following years, it spread to Bursa, Istanbul, Sakarya, Kocaeli, Balıkesir, Bilecik, Düzce, Giresun, Bartın, Zonguldak, Sinop and İzmir provinces. In this study, the orchard of chestnut gene resources belonging to the Ali Nihat Gökyiğit research station in Samsun province was examined for the presence of the Asian chestnut gall wasp. As a result of the study, the presence of the Asian chestnut gall wasp was determined in the cultivars Marigoule' and 'Macit 55'. As a result of the counts made in 50 cm parts of the branches, it was determined that the presence of chestnut gall wasp is in a higher population in the 'Marigoule' cultivar than in the other cultivars. However, the invasion in Samsun is at the early stage.

Estimating the potential threat of increasing temperature to the forests of Turkey: a focus on two invasive alien insect pests

Rising temperature can affect forests negatively through its impact on insect pests. The present study focused on two invasive alien insect species (Dryocosmus kuriphilus and Leptoglossus occidentalis) to understand how rising temperature might affect their damage in Turkish forests. For D. kuriphilus, the timing of chestnut budburst, gall induction and emergence of its introduced parasitoid, Torymus sinensis, were monitored between 2015 and 2019, and each phenological event was compared annually with fluctuations in temperature to observe the parasitoid-host synchrony. For L. occidentalis, cumulative degree days (CDD) were calculated, and the possible number of generations produced in 2020 in different regions of Turkey were predicted. The CDD calculations were repeated under increasing temperature and different photoperiod-diapause induction scenarios. Evaluation of the monitoring data on the D. kuriphilus system showed that gall induction occurred at the same time as budburst, whereas T. sinensis emergence was independent from the budburst, and that the parasitoid-host synchrony was disrupted after the abnormally warm winter in 2018. The CDD calculations estimated that L. occidentalis produced one to five generations from north to south in 2020. They also suggested a significant increase in the number of generations in the southern Turkey under temperature increase scenarios. Including photoperiod as a time-limiting factor reduced the highest possible number of generations from five to two. In conclusion, rising temperature has a potential to threaten the biocontrol against D. kuriphilus, and it can increase voltinism in L. occidentalis.

Assessment of Chestnut Gall Toughness: Implications for a Biocontrol Agent.

(1) Torymus sinensis, the biocontrol agent of the Asian chestnut gall wasp Dryocosmus kuriphilus, is univoltine, but in NW Italy a small percentage of individuals exhibits a prolonged diapause, mainly as late instar larva. (2) In 2020, the diapause was investigated to evaluate its trend over the years. Due to the low survival rate of diapausing T. sinensis adults, the seasonal variation in the galls' toughness was evaluated, thus assuming that dry galls over time can negatively affect emergence. The window of vulnerability of the gall wasp galls was also evaluated in controlled conditions. (3) The results showed that the average number of second year T. sinensis emerging per 100 cells was 0.41 ± 0.05, and dead adults accounted for 4.1 ± 0.23 per 100 cells. Gall toughness resulted in lower values for galls collected in May and June, and then gradually increased over time. In general, no difference was detected in the wall toughness of galls formed during the previous year when compared to current-year dry galls. Oviposition was recorded on all the tested galls collected in May and June, and no difference in the number of oviposition events was detected. Conversely, no oviposition was observed in July. Comparing the number of oviposition events by T. sinensis and the gall toughness, a negative correlation was found (R2 = -0.99). (4) The present findings contribute descriptive information on this gall's structural traits, and the influence on gall wasp management is also discussed.

Defensive patterns of chestnut genotypes (Castanea spp.) against the gall wasp, Dryocosmus kuriphilus

Plants draw from various genetically controlled defenses to protect against herbivores and pathogens. The efficacy of alternative defenses can vary with the biology and phylogeny of the enemy.Dryocosmus kuriphilus, an invasive gall maker native to China, has become one of the main pests of chestnut trees around the world. We studied genetic variation in resistance and susceptibility toD. kuriphiluswithin a replicated blocked planting of 12 chestnut genotypes established in Galicia, Spain in 2004. We found very high genetic variation in susceptibility toD. kuriphilus. We evaluated if the variation was due to host selection by the wasp, differential efficacy of inducible defenses in the trees, or variability in susceptibility of the plant to manipulation by the gallmaker. We assessed host selection by counting number of eggs laid by females in tree buds and comparing preferences with phytochemistry. We also measured inducible changes in phytochemistry within and around galls, gall physical characteristics, parasitism, and insect fitness. The effective defense mechanisms in resistant genotypes involved (1) hypersensitive reactions to eggs or neonates within buds and (2) early precise abscission of nascent galls from expanding leaves. Surprisingly, the genetic resistance toD. kuriphilusof the chestnut genotypes we tested was not related to phenols, terpenes, and primary nutrition.

Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae) in Minho (Northern Portugal): Bioecology, Native Parasitoid Communities and Biological Control with Torymus sinensis Kamijo (Hymenoptera: Torymidae)

The Asian chestnut gall wasp Dryocosmus kuriphilus Yasumatsu, native to China, was first detected in Europe in Italy in 2002. In Portugal it was declared in 2014, and it has since affected the Portuguese chestnut production. The introduction of its natural parasitoid Torymus sinensis Kamijo started through inoculative releases according to the National Action Plan for the Control of Dryocosmus kuriphilus, established by the Direção Geral de Alimentação e Veterinária (DGAV), in 2015. This research was carried out during 2018 and 2019, in five chestnut orchards in the Minho region (Northern Portugal). Between January and March 2018, at each location, three monthly harvests of 100 buds were carried out to determine the infestation level. Between April and June 2018, 240 galls were harvested every two weeks, with the purpose of studying the bioecology of D. kuriphilus. In each sampling site, 160 galls were placed in emergence boxes to follow adults of the D. kuriphilus population, and 80 galls were dissected with a binocular magnifying glass, to count and record the evolution of the larval stages of D. kuriphilus and of the parasitoids. The identification of T. sinensis and native parasitoids was carried out. The parasitism rates and Simpson diversity indices were determined. The percentage of buds infested by D. kuriphilus was high in all studied places, varying between 67% and 80%, regardless of the number of T. sinensis releases made and of the chestnut cultivars present in each orchard. The highest rate of parasitism by T. sinensis was 0.5044% and it was recorded in an orchard where there were two releases of T. sinensis in 2016 and 2017 (Arcos de Valdevez—Rio Cabrão—P1). Considering that the exotic parasitoid has already been released in the region since 2016, its establishment in all the chestnut orchards studied was confirmed, although with very low parasitism rates. The natural parasitism associated with the native parasitoid species of D. kuriphilus was confirmed in this work, recording values between 34% and 51% of the parasitized chestnut galls, with 11 species of native parasitoids having been identified: Eupelmus azureos, Eupelmus uruzonus, Eurytoma brunnivientris, Eurytoma pistaciae, Megastigmus dorsalis, Mesopolobus sp., Ormyrus pomaceus, Sycophila biguttata, Sycophila iracemae, Sycophila variegatta and Torymus flavipes.

A mismatch in the emergence of Torymus sinensis may affect the effectiveness of this biocontrol agent?

The biocontrol agent Torymus sinensis Kamijo is considered as one of the most successful examples of classical biological control programs. This parasitoid represented a feasible option to obtain sufficient, sustainable, and long-term control of the Asian chestnut gall wasp (ACGW), Dryocosmus kuriphilus Yasumatsu. Recently, an unusual presence of galls was recorded in a few chestnut orchards of Northern Italy, although T. sinensis was released in previous years. We hypothesized that the increase in infestation rate over the years was related to a mismatch in the parasitoid/host phenology, resulting in a decrease in biocontrol effectiveness. Investigations were performed in the five-year period 2018–2022 in six chestnut orchards, selected according to the ACGW infestation level, and divided in two categories: non-critical sites (negligible presence of ACGW galls) and critical sites (high presence of galls with suppression of bud growth). We evaluated T. sinensis’s parasitism rate and phenology by dissecting chestnut galls, comparing non-critical sites versus critical sites. Temperatures were monitored in all the orchards with data loggers. In non-critical sites the parasitism rate by T. sinensis was stable and/or growing in all years, accounting from 77% to 99% (i.e., total number of T. sinensis divided by total number of larval chambers). Conversely, the parasitism rate in critical sites experienced a severe decline, reaching values under 50% in all sites in 2021–2022. Specifically, parasitism on average was reduced by 44% when comparing 2019 versus 2022. The dissection of the galls recorded in non-critical sites in winter (February) highlighted that on average most T. sinensis were larvae and immature pupae (about 70%). Conversely, in critical sites most of the individuals were black mature pupae (76%), with presence of newly formed adults (12%). In 2019–2022, the mean temperature recorded in critical sites was 2.72 °C and 2.34 °C higher in January and February respectively, when compared to non-critical sites. Moreover, in critical sites the early emergence of the biocontrol agent (late February-early March) was recorded when current-year ACGW fresh galls were not available. No variation in the phenological cycle of the ACGW was ever observed, in all sites and years. Our results suggest that the asynchrony between T. sinensis and the ACGW heavily affected the role of the released agent in the suppression of the pest’s outbreaks. Future studies are needed to clarify whether this event is increasing in relevance, also in a climate change perspective.

A Review of the Stress Resistance, Molecular Breeding, Health Benefits, Potential Food Products, and Ecological Value of Castanea mollissima.

Chestnut (Castanea spp., Fagaceae family) is an economically and ecologically valuable species. The main goals of chestnut production vary among species and countries and depend on the ecological characteristics of orchards, agronomic management, and the architecture of chestnut trees. Here, we review recent research on chestnut trees, including the effects of fungal diseases (Cryphonectria parasitica and Phytophthora cinnamomi) and insect pests (Dryocosmus kuriphilus Yasumatsu), molecular markers for breeding, ecological effects, endophytic fungi, and extracts with human health benefits. We also review research on chestnut in the food science field, technological improvements, the soil and fertilizer used for chestnut production, and the postharvest biology of chestnut. We noted differences in the factors affecting chestnut production among regions, including China, the Americas, and Europe, especially in the causal agents of disease and pests. For example, there is a major difference in the resistance of chestnut to C. parasitica in Asian, European, and American countries. Our review provides new insights into the integrated disease and pest management of chestnut trees in China. We hope that this review will foster collaboration among regions and help to clarify differences in the direction of breeding efforts among countries.

The Oriental Chestnut Gall-wasp Dryocosmus Kuriphilus Yasumatsu, 1951, (Hymenoptera: Cynipidae) and Its Introduced and Native Parasitoids in Madeira Island, Portugal, with Notes on Some Other Parasitic Hymenoptera Reared from Gall Samples

The accidental introduction to Madeira of the invasive chestnut gall wasp (CGW), Dryocosmus kuriphilus, is reviewed, as is the subsequent biological control programme implemented by the Regional authorities. This control programme was based on the importation of a non-native parasitoid, Torymus sinensis. Results from five years of parasitoid release are presented, including a list of native parasitoid species associated with D. kuriphilus galls in Madeira. Five species of Hymenoptera are listed as new records for Madeira: Dryocosmus kuriphilus Yasumatsu, 1951; Torymus sinensis Kamijo, 1982; Bootanomyia dorsalis (Fabricius, 1798); Colpoclypeus florus (Walker, 1839), and Ufens foersteri (Kryger, 1918).

Textile Physical Barriers against the Chestnut Gall Wasp Dryocosmus kuriphilus

Dryocosmus kuriphilus Yasumatsu is a species originating from China that, during the 20th century, has spread rapidly throughout many countries, affecting mainly different species of the genus Castanea spp. In fact, it is considered to be the most important pest of chestnut trees (Castanea sativa Miller), causing significant production losses. The adoption of complementary measures to chemical and biological controls would contribute to the control of the pest. In this sense, the use of textile physical barriers could prevent the rapid spread of this species among the production centers. Therefore, the objective of this study is to define the characteristics of a textile that protects young plants that have been produced in nurseries. For this purpose, some commercial textiles have been selected based on the morphometric characterization of the species and these textiles have been accurately measured in order to compare their dimensions with those of the insects. Finally, tests have been carried out in order to measure the efficacy of the textiles under laboratory conditions, controlling the air velocity and the temperature. The results reveal that, in general, theoretical efficacy may not be a good predictor of practical results. A fully effective screen has been found against this species and its design characteristics can be used as a starting point for new, more optimized designs.

Egg maturation in an invasive gall wasp, Dryocosmus kuriphilus (Hymenoptera: Cynipidae): An experimental test of the pro-ovigenic and facultatively synovigenic hypotheses

There are two hypotheses on egg maturation in the invasive chestnut gall wasp, Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae). That it is pro-ovigenic (most or all of its potential lifetime egg complement is mature upon emergence) or facultatively synovigenic (not all eggs are fully developed upon emergence and may be resorbed when suitable hosts are absent). These hypotheses were tested by determining the effects of adult age and food (honey) on egg maturation in D. kuriphilus wasps with no access to host plants. Egg load (the number of mature eggs per female) neither increased nor decreased with adult age in the presence or absence of honey when deprived of host plants. These findings support the pro-ovigenic hypothesis. Some eggs mature during the adult lifetime of cynipoid parasitoids even without hosts, but the cynipoid gall inducer, D. kuriphilus, is pro-ovigenic, probably due to the abundance of chestnut buds available for oviposition under natural conditions. In addition to no competition for oviposition resources, thelytokous reproduction, unintentional introduction of infested chestnut trees and escape from host-specific parasitoids in introduced countries, pro-ovigeny with a high egg load has presumably resulted in D. kuriphilus becoming a global pest of chestnuts. In addition, body length, mesosomal and metasomal lengths and widths, hind femoral length, hind tibial length, and egg load as well as egg width of this wasp were also measured. There was no variation in egg width, but all the other measurements were positively correlated with egg load. Large females of D. kuriphilus had higher egg loads than small females.

Phenology, Density and Parasitism of Asian Chestnut Gall Wasp (Dryocosmus kuriphilus) (Hymenoptera: Cynipidae) in Recently Invaded Chestnut (Castanea spp.) Orchards in Michigan.

Asian chestnut gall wasp (ACGW) (Dryocosmus kuriphilus Yasumatsu), an invasive pest native to China, was detected in Michigan, the largest chestnut producer in North America, in 2015. Along with quantifying gall densities, we tracked dates and cumulative growing degree days corresponding to ACGW life stages in five, seven, and nine orchards in 2017-2019, respectively. Gall formation, triggered by the onset of feeding by overwintered larvae, began soon after bud break. Most adult wasps emerged in mid summer, after pollen production peaked. Density of ACGW in all sites dropped sharply in 2019, probably as a result of larval mortality caused by severely cold temperatures in late January. Gall density was generally lower on Chinese chestnut (Castanea mollisima Blume) trees and C. mollisima hybrids, which share some coevolutionary history with ACGW, than on cultivars of European chestnut (C. sativa Miller) and Japanese-European (C. crenata Sieb. & Zucc. x C. sativa) trees, including the popular Colossal cultivar. Torymus sinensis Kamijo (Hymenoptera: Torymidae), a larval parasitoid previously introduced into the U.S. and several countries in Asia and Europe for ACGW biocontrol, appears to be spreading with ACGW in Michigan. Parasitoid larvae were recorded in four, six, and eight of the infested sites we sampled in 2017-2019, respectively, and parasitism rates ranged from 5 to70% of galls.

Host Gall Size and Temperature Influence Voltinism in an Exotic Parasitoid

Insect phenology is highly temperature-dependent. Higher temperatures can lead to earlier emergence and lengthening of the active period, which enable many insect groups to complete more generations. Studies on the effects of climate change on insect populations are providing concerning evidence supporting this relationship. These kind of shifts in phenology and voltinism also occur in agricultural and forest insect pests and their natural enemies, with potential implications for biological control. The consequences derived from changing temperature regimes on tritrophic interactions remain poorly studied, particularly in gall-inducing insects and their parasitoids. Here we detail the occurrence of bivoltinism in the exotic parasitoid Torymus sinensis, previously categorized as univoltine, a widely introduced species to fight against the invasive Asian chestnut gall wasp Dryocosmus kuriphilus wherever this pest spread. This plasticity in voltinism has been observed in the southernmost European distribution of D. kuriphilus, and appears to be mediated by both temperature and gall traits, namely size or the number of gall chambers. Bivoltinism was most common at annual mean temperatures around 13.5°C and in galls with more chambers. Through this work, we intend to unravel the factors behind this phenomenon and discern the possible consequences on host-parasitoid interactions.

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

Simple SummaryThe insect Dryocosmus kuriphilus induces galls on chestnut trees. Torymus sinensis is a host-specific parasitoid of D. kuriphilus and phenologically synchronizes with D. kuriphilus. 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 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. 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.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.

Susceptibility levels of some chestnut cultivars and genotypes to the chestnut gall wasp in Turkey

The Asian chestnut gall wasp (ACGW) is one of the most important pests threatening most Castanea species. The best management strategy against this pest can be establishing new orchards with resistant cultivars along with biocontrol (parasitoid Torymus sinensis Kamijo (Hymenoptera: Torymidae)). In Turkey, ACGW was first detected in 2014 at Gac?k village of Yalova province. Bursa, ?stanbul, Sakarya, Kocaeli, Bal?kesir, Bilecik, D?zce, Giresun, Bart?n, Zonguldak, Sinop and ?zmir provinces are also infected with ACGW. This study was carried out to determine the levels of susceptibility of chestnut cultivars/genotypes to ACGW. The study was carried out in Yalova province between 2016 and 2018. In total, 15 cultivars/genotypes were involved in the study, including European (C. sativa) chestnuts (Albayrak, Alt?nay, ?Erfelek?, ?Osmano?lu?, Sal?pazar?, ?Serdar?, ??nal?), interspecific hybrids (?Marigoule? and BDB-L) and complex hybrids (?Aky?z?, ?Macit 55?, ?Ali Nihat?, A9, A55, A56) were tested in the study. In April 2016, five- to seven-year-old seedlings were ?bark? grafted, and susceptibility to the ACGW was evaluated by recording the ratio of infected buds (%), visual assessment of the damage (severity), and calculations of an infestation index. Among the cultivars and genotypes tested in the study, the ?Aky?z? cultivar was determined to exhibit the highest resistance against the ACGW. To fully understand the resistance mechanism of the ?Aky?z? cultivar, molecular and biochemical studies should be done and compared with other results.

Local-scale dispersal patterns and susceptibility to Dryocosmus kuriphilus in different Castanea species and hybrid clones: insights from a field trial

The chestnut gall wasp Dryocosmus kuriphilus is a major insect pest affecting chestnut trees worldwide. Medium and long-term control of this pest can be improved by using resistant or less susceptible cultivars and hybrid clones. In addition, little is known about the local patterns of dispersal of the pest. We obtained data from trees of 3 chestnut species and 27 hybrid clones in a field trial in NW Spain with the aim of evaluating the susceptibility of the material to the gall wasp and identifying possible drivers of local spatial dispersal. In the first 3 years of the invasion by D. kuriphilus, the number of trees attacked and the number of galls on each tree were spatially clustered. Tree height significantly predicted both variables, suggesting that gall wasps may use visual cues to locate suitable host trees, at least in the early stage of invasion. Assessment of the susceptibility of hybrid clones/pure species must take concurrent indicators of infestation levels into account. We suggest the use of indices involving galls on shoots because these enable good assessment of the damage to chestnut trees. The study findings add to existing knowledge on the susceptibility of hybrid chestnut clones. We report, for the first time, two hybrid clones resistant to the pest and one hybrid clone which exhibited consistently low values for all of the indicators of infestation level. The results have important implications regarding selection of plant material for use in afforestation in Spain, where the current high rate of chestnut planting is expected to continue.