Temporal changes in the composition of parasitoid assemblages associated with the invasive chestnut gall wasp

Abstract

Invasive alien species pose a challenge to ecosystem stability and crop production, so understanding their interactions with the natural communities they invade is cru cial to mitigate negative effects. The oriental chestnut gall wasp, Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae), is an invasive insect that attacks chestnut trees. It was first recorded in Spain in 2012 and is now presumably present in the majority of chestnut stands in the country. We assessed variation in the abundance of D. kuriphilus galls and the composition of their associated parasitoid community (Hymenoptera: Chalcidoidea) during a 4- year period (2014–2017) in 12 sampling sites in Catalonia (Spain, northeastern Ibe rian Peninsula), and identified which species contributed most significantly to the control of D. kuriphilus.The results show that the abundance of individual parasitoid species varied during the study period and that the number of species increased year after year. There was also a transition in the parasitoid community composition across the years. Our data suggest that the joint action of the non-native parasitoid Torymus sinensis Kamijo and the native T. notatus (Walker) (Hymenoptera: Chalcidoidea: Torymidae) led to the decline of D. kuriphilus until it was no longer considered a pest. Also, the observed pool of parasitoid species ended up being relatively homogeneous across sites over the years, which may be due to the high natural dispersal of these parasit oids (both by active flight and passive wind dispersal).