Classical biological control against the chestnut gall wasp Dryocosmus kuriphilus (Hymenoptera, Cynipidae) in France

Considered as a major pest of Castanea species worldwide, the chestnut gall wasp Dryocosmus kuriphilus Yasumatsu (Hymenoptera, Cynipidae) can induce fruit production losses of 60-80%. Reported for the first time in Italy in 2002, this pest is now widespread across the French distribution of chestnut trees. Based on successful attempts in other countries, a classical biological control program using the parasitoid Torymus sinensis Kamijo (Hymenoptera, Torymidae) has been implemented in France since 2011. Three main objectives were delineated for the program. The first is long-term control of chestnut gall wasp populations, be it in commercial orchards or in forests. The second objective is to take advantage of planned introductions of T. sinensis to better understand factors that underpin the establishment and spread of exotic species. The third objective is to describe the recruitment of native parasitoids by invasive D. kuriphilus and to assess the impacts of T. sinensis on native communities. During the two first years of this project, 42 releases of T. sinensis were achieved with an experimental manipulation of propagule pressure. Initial results indicate that: (i) T. sinensis has successfully established in at least 20 of the release sites; (ii) T. sinensis populations, as well as populations of native parasitoids, have a positive inter-annual growth rate; and (iii) no significant impacts of parasitoid introductions on the chestnut gall wasp have been observed yet.