Effects of environmental parameters on the chestnut gall wasp and its complex of indigenous parasitoids

The chestnutgallwasp(CGW), Dryocosmuskuriphilus, aninvasivepestnativetoChina,has caused severeyield and economic losses to chestnut production in Europe since its arrival in 2002. In Southern Italy, the complex of indigenous parasitoids colonizingCGWwasmonitoredbetween2013and2015,withtheaimofestimatingthecompositionoftheindigenousparasitoid complex, its ability to control CGW populations, and the interactions of both factors with several measured environmental parameters. We compared results among three differently managed field types. Results showed an increase in the rate of parasitism both when the host population density was lower and in unmanaged chestnut stands with more natural conditions. The percentage of parasitism in galls was related to morphological traits of the galls and to higher seasonal temperatures, which reducedtheparasitismintensitybecauseCGWdevelopsearlierundersuchconditions.Thehost–parasitoidmortalityinsidegalls varied among sites and was associated mostly with rot fungi during wet spring and summer months. Parasitoid species richness was similar among the study sites, but the proportion of parasitoid species differed between orchards and unmanaged coppice stands. The timing of attack by parasitoids followed a species-specific successional sequence throughout the larva-to-adult life cycle of the CGW. These interactions should be considered in future research on trophic relationships and when modeling invasive scenarios for new pest species.