ABOVE-GROUND STORAGE OF PARASITIZED DRYOCOSMUS KURYPHILUS CHESTNUT GALLS INCREASES SURVIVAL OF OVERWINTERING TORYMUS SINENSIS IMMATURES

The gall-inducing Asian Chestnut Gall Wasp (ACGW), Dryocosmus kuriphilus is one of the most harmful pests of Castanea species in the world. In 2005, Torymus sinensis, a species-specific parasitoid of the ACGW, native to China, was released in Italy as a biological control agent. After more than ten years from the first T. sinensis release, ACGW only sporadically affects chestnut production. However, some areas of Tuscany such as Villore (Tuscany, Italy) still remain active ACGW hotspots and even though its distribution is much more jeopardized than in the past, several recurrent outbreaks have been recently reported. In the present work, we evaluated the possibility of storing leaf galls in the field, during the cold season, in order to protect T. sinensis immatures overwintering within them. In particular, the hypothesis was tested that above-ground storage of leaf galls could increase parasitoid survival in a Castanea sativa orchard near Villore (Tuscany, Italy). Results showed that T. sinensis survival in leaf galls stored above ground was higher than that recorded on galls stored on the ground, proving that this method was effective in protecting overwintering immatures from adverse environmental conditions. Our study provided chestnut growers with a new tool aimed at enhancing T. sinensis activity in C. sativa orchards.