Sweet chestnut Castanea sativa orchards are part of traditional farming in many areas of Italy (and elsewhere in Europe); they are also important for wildlife. Native to China, the chestnut gall wasp Dryocosmus kuriphilus was first recorded in the Piedmont region (northwest Italy) in 2002 (introduced via nursery material from China 2-3 years earlier). It had spread throughout much of Italy by 2005, and was also recorded in neighbouring Slovenia and southeast France. The wasp causes gall formation on chesnut buds which reduce photosynthetic area, may retard shoot growth and greatly reduced fruit production. Trees may decline gradually in health, become more susceptible to disease and eventually die.
D.kuriphilus was successfully controlled in Japan (where also accidentally introduced) by introducing a parasitoid wasp, Torymus sinensis (Hymenoptera: Torymidae), from China in the late 1970s. After about 6-18 years the parasitoid effectively controlled the gall wasp. Measures to support its introduction to Italy commenced in 2003 with a survey of relevant literature and contact with Japanese researchers.
About 28,010 galls were received from Japan over 3 years (2004-06). From these, 2,117 T.sinensis were released into chesnut woodlands at 11 sites, over 2 years (2005-06) in the province of Cuneo in Piedmont.
In the 2006/2007 winter at four of these sites (Robilante, Peveragno, Boves and the rearing area), a large sample of galls (formed during the previous spring) was collected from various heights in chesnut trees using lopping shears. The effectiveness of the releases was assessed by examining the emergence of T.sinensis from these galls.
Of 64,000 galls collected, 204 T.sinensis emerged, indicating that T.sinensis had laid eggs successfully in Italian galls in the wild. This is considered promising at this early stage baring in mind the limited releases and monitoring effort. In the chestnut woods sampled, D.kuriphilus galls were estimated to be present in millions; so the probability of finding parasitized galls was expected to be lower than that in fact observed. Monitoring is ongoing but results obtained so far suggest that T.sinensis establishment in Italy is quite likely.