Interactions between Nuclear Polyhedrosis Virus and Three Larval Parasitoids of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

Abstract

Interactions between a Helicoverpa nuclear polyhedrosis virus (NPV) and three larval parasitoids of H. armigera were recorded in laboratory studies. the parasitoids Microplitis demolitor, Cotesia kazak and Hyposoter didymator required a time advantage of at least 3 d at 25°C before the host was exposed to NPV to ensure successful completion of development. Helicoverpa larvae parasitised by C. kazak died from NPV after the parasitoids emerged from the host, and thus could provide a source of virus inoculum for secondary spread of the disease. On the other hand, as the interval between parasitisation and host exposure to NPV increased, the proportion of hosts parasitised by M. demolitor which died from NPV after emergence of the parasitoid decreased. It was also shown that as the time interval between host parasitisation by M. demolitor and exposure to virus increased, higher virus doses were required to kill parasitised hosts than were required for nonparasitised hosts of the same age.