Assessment of Chestnut Gall Toughness: Implications for a Biocontrol Agent

SIMPLE SUMMARY: Torymus sinensis, the biocontrol agent of the gall wasp Dryocosmus kuriphilus, is univoltine, and exhibits a prolonged diapause. Further investigations have been carried out to assess the extent of the diapause and its trend over the years. Moreover, the seasonal variation in the galls’ toughness was measured to assess if the wall of dry galls formed in the previous year was so hard to counteract T. sinensis emergence, thus negatively affecting diapause. The window of vulnerability of the galls was also evaluated in controlled conditions. 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. In general, no difference was detected in the wall toughness of galls formed during the previous year when compared to current-year dry galls. Comparing the number of oviposition events by T. sinensis and the gall toughness, a negative correlation was found. Descriptive information on this gall’s structural traits and the influence on gall wasp management are also discussed. ABSTRACT: (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 (R(2) = −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

The Box Tree Moth: An Invasive Species Severely Threatening Buxus Natural Formation in NW Italy

(1) The box tree moth (BTM), Cydalima perspectalis Walker, represents one of the recent examples of exotic insect pests native to Asia accidentally introduced in Europe by the nursery trade. In Europe, BTM develops on Buxus sempervirens L., causing significant damage to ornamental and natural plants. (2) Basic aspects of BTM biology were investigated at three sites in the NW Alps, where B. sempervirens occurs on rocky slopes, forming a protected habitat. In 2019–2021, we evaluated: (i) the seasonal flight activity with sex pheromone traps, (ii) the fecundity and the effects of food on the egg load, (iii) the potential adaptation of BTM on native secondary host plants, and (iv) the recruitment of natural enemies. (3) Our results revealed the presence of two generations per year. The number of mature eggs increased in fed adults and was higher in females of the first generation. No evidence of BTM shift on secondary plants was found in either laboratory or natural conditions, and no significant occurrence of natural enemies was recorded, except for one pupa of the tachinid Pseudoperichaeta nigrolineata. (4) Our findings provide valuable information to address and timely plan management strategies to preserve B. sempervirens as an essential component of rare forest ecosystems

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

Pheromone-Mediated Mating Disruption as Management Option for Cydia spp. in Chestnut Orchard

(1) Background: Pheromone-based devices are successfully used to control insect pests in agriculture. (2) Methods: Investigations were conducted to evaluate the effectiveness of mating disruption (MD) to control the chestnut tortrix moths, Cydia fagiglandana and Cydia splendana. Surveys were performed in northern Italy in 2019–2020. MD was carried out using the pheromone dispenser Ecodian® CT. The effectiveness of MD was assessed by recording male adult catches in pheromone-baited sticky traps and larvae in chestnut fruits, comparing MD and control plots. (3) Results: The total number of trapped males was significantly lower in MD plots than in control ones, for all sites and years. Trap catch suppression in MD plots averaged 89.5% and 93.8% for C. fagiglandana and 57.4% and 81% for C. splendana in 2019 and 2020, respectively. The larval infestation rate in fruits did not vary between plots except for one site where a reduction of about 71% in the MD plot was recorded in 2019. (4) Conclusions: Low catches in MD plots turned out to be a good measure of the effectiveness of communication disruption, but no satisfactory data have been obtained regarding fruit infestation, highlighting how the reduction of male catches cannot always be considered as a reliable indicator of successful control. Specific investigations about background population density, dispersal and mating/oviposition behavior are thus essential for a viable management strategy