Chalcid parasitoid community associated with the invadingpest Dryocosmus kuriphilus in north-western Italy

1. Biological invasions of exotic species pose a major threat to native bio- diversity. Invaders are known to have direct im pacts on native species; however, less well studied are the indirect impacts media ted through the integration of invaders into trophically linked communities. 2. A survey of the chalcid wasp parasitoid c ommunity attacking t he chestnut gall- wasp Dryocosmus kuriphilus was carried out over a 5-year period at 26 sites in north- western Italy. More than 415 000 galls wer e collected and more than 10 000 parasit- oid specimens emerged. Twenty-seven parasitoid species belonging to six families (Eurytomidae, Pteromalidae, Torymidae, Eupelmidae, Ormyridae, Eulophidae) were identified using morphological and molec ular methods; seventeen are new records for the parasitoid community associated with D. kuriphilus in Italy. The morphospe- cies complexes Megastigmus dorsalis , Eupelmus urozonus, E. annulatus ,and Eurytom- apistaciae 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 s pecies 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 mak ing life-history decisions to take advan- tage 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 commu- nities via indirect competition med iated through shared parasitoids