105 Torymus sinensis: Biology, Host Range and Hybridization A. Quacchia S. Moriya GreenWood Service Srl National Agricultural Research Center Torino Tsukuba Italy Japan R. Askew K. Schönrogge Beeston, Tarporley Centre for Ecology & Hydrology Cheshire Crowmarsh Gifford, Wallingford, OX10 8BB UK Oxfordshire UK Keywords: parasitoid, biological control, Torymidae, diapause, gall wasp, mate recognition, Dryocosmus kuriphilus Abstract Torymus sinensis is a parasitoid of the chestnut gall wasp Dryocosmus kuriphilus, introduced as a biological control agent into Japan, USA, and since 2005, into Europe. Although its effectiveness in controlling the pest was confirmed, some important aspects of its biology, including risks to non-target species, are still unknown or at most scarcely investigated. The results of the present study address an important aspect of the life-cycle of T. sinensis: the existence of extended diapause. Behavioural experiments confirm high levels of host specificity by the parasitoid and suggest that interbreeding with native Torymus species is highly unlikely. INTRODUCTION Torymus sinensis Kamijo (Hymenoptera: Torymidae) is a solitary ectophagous parasitoid of the global pest Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae), the chestnut gall wasp. It originates, like its host, from China and is the only parasitoid species of D. kuriphilus known to be both host specific and phenologically well-synchronized with D. kuriphilus (Moriya et al., 2003). T. sinensis females lay eggs in newly-formed D. kuriphilus galls in early spring. Unfertilized eggs develop into haploid males and fertilized eggs develop into diploid females (haplodiploidy). The parasitoid larva feeds ectophagously on the host larva. By late spring the mature larva (with characteristic brown stripes on the abdomen) has already stopped feeding, but it does not pupate until winter and the adult emerges the following spring. After the accidental introduction and rapid range expansion of the chestnut gall wasp in Japan (in the 1940s), USA (in the 1970s) and Italy (in the 2000s) T. sinensis was intentionally introduced into these countries as a biological control agent (Quacchia et al., 2008), partly because native species of gall wasp parasitoids in the invaded ranges failed to regulate D. kuriphilus populations (Quacchia et al., 2013a). The effectiveness of T. sinensis in controlling the pest was confirmed first in Japan (Moriya et al., 1989) and recently in Italy (Quacchia et al., 2014), but some aspects of its biology are still unknown, or at most scarcely investigated. This includes risks to non- target species through host-shifting, or hybridization with native Torymus species. Neither of these potential problems have been studied or tested in any detail, in either its native or its introduced ranges, in the laboratory or field (EFSA, 2010; Gibbs et al., 2011). Here we present the results of laboratory tests performed to investigate these important aspects of its biology. Proc. II nd European Congress on Chestnut Eds.: L. Radócz et al. Acta Hort. 1043, ISHS 2014