Native and introduced parasitoids attacking the invasive chestnut gall wasp Dryocosmus kuriphilus

Abstract

The globally invasive chestnut gall wasp Dryocosmus kuriphilus was recently reported in Italy and threatens European chestnut orchards and native forests. Of Chinese origin, this species has invaded Japan, Korea, the USA, Nepal and Europe and in each region it has been attacked by parasitoids exploiting oak gall wasps. Classical biological control using the parasitoid Torymus sinensis (Hymenoptera: Torymidae) successfully reduced infestation in Japan. Subsequent work in Japan and Korea showed this parasitoid to represent a poorly understood and biologically diverse species complex. Following its success in Japan, T. sinensis was released in Italy in 2005. A growing appreciation of the taxonomic and ecological complexity of the T. sinensis complex in Japan and Korea has stimulated ongoing DNA‐based work on relationships and interbreeding of species in this group. Oak cynipid parasitoids provide potential for native augmentative or conservation biological control of D. kuriphilus in Europe. Exploitation of this potential requires improved understanding of the taxonomy of these parasitoids, particularly of morphologically highly conserved lineages such as Eurytoma and Eupelmus in which recognised species may contain many cryptic lineages. There is a growing need for a molecular survey of the communities centered on chestnut and oak gall wasps to: (1) ascertain the identity of T. sinensis lineages released in Italy (2) track the dispersal of T. sinensis in the native community, either in its original form or as hybrids with native species (3) identify possible biological control agents in the native parasitoid community.