Environmental thermal levels affect the phenological relationships between the chestnut gall wasp and its parasitoids

Studies of thermal level-related asynchrony in a host-parasitoid relationshipare necessary to understand the effects of climate change on new host-parasitoidinteractions. In the Asian chestnut gall wasp Dryocosmus kuriphilus (Hymenoptera:Cynipidae) and its Chalcidoidea parasitoids, phenological synchrony is assumed to beweather-dependent in a new area of expansion. To evaluate the effects of environmentalthermal regimes on the host, a phenology model for different cynipid stages (larvae,pupae, adults, and adult emergence) and a host-parasitoid phenological estimator aredeveloped in three chestnut fields during two successive growth seasons and subsequentlyvalidated in areas with chestnut fields at two different altitudes. Comparisonsof the timings of the juvenile and adult stages with those of the parasitoid complexdemonstrate that the shortest period of occurrence for cynipids within galls has negativeeffects on the host-parasitoid relationships at higher temperature levels, thereby increasingphenological asynchrony for some parasitoids species. Reducing the developmenttime of pupae and adults decreases the likelihood of success for some parasitoid speciesat higher temperature levels. We also record the extension of the gall wasp developmenttime (approximately 15 days) at higher altitudes (linked to a lower mean temperature ofapproximately 1.5?C). These results highlight how parasitization on the new hosts isdependent on the host phenology and, in the present study, is limited by the short durationof the presence of the host in galls, which could explain the considerable differencesin cynipid gall wasp parasitization recorded at different altimeters.