Ruolo dei parassitoidi autoctoni e di quello esotico introdotto nel controllo biologico del cinipide galligeno del castagno in Sardegna

The Asian chestnut gall waspDryocosmus kuriphilusYasumatsu (Hymenoptera, Cynipidae) (ACGW) is considered as a major pest of Castanea species worldwide. The classical biological control based on the release of the parasitoidTorymus sinensisKamijo (Hymenoptera, Torymidae) is considered to be the only effective method of controllingD. kuriphilus.The parasitism rates of native parasitoids species are typically low (2-10%), thus they cannot control chestnut gallwasp keeping its population below an economic threshold. A multi-year monitoring of exotic and native parasitoids of this pest was carried out in Sardinia by collecting specimens inside the galls. At the same timeD. kuriphilusinfestation andT. sinensissettlement in some release sites has been monitored.The data collected clearly indicate thatD. kuriphilusis decreasing as demonstrated by the decrease of number of galls, infested shoots and number of cells per gall.Until 2014, the density ofT. sinensishas been extremely low in sites different from those of release reaching levels well below those relative to native parasitoids (between 40 and 50%). However, in two years since thenT. sinensisbecame the dominant species in some sites parasitizing 99% of gall wasp cells.T. sinensisis well established in all release sites but some differences were in density values between galls collected in spring-summer (diapausing larvae) and emergences from “winter” galls suggesting some mortality of overwintering larvae.