INTERACTIONS BETWEEN NUCLEAR POLYHEDROSIS-VIRUS AND 3 LARVAL PARASITOIDS OF HELICOVERPA-ARMIGERA (HUBNER) (LEPIDOPTERA, NOCTUIDAE)

Interactions between a Helicoverpa nuclear polyhedrosis virus (NPV) an d three larval parasitoids of H. armigera were recorded in laboratory studies. The parasitoids Microplitis demolitor, Cotesia kazak and Hypo soter didymator required a time advantage of at least 3 d at 25 degree s 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 provid e a source of virus inoculum for secondary spread of the disease. On t he other hand, as the interval between parasitisation and host exposur e to NPV increased, the proportion of hosts parasitised by M. demolito r which died from NPV after emergence of the parasitoid decreased. It was also shown that as the time interval between host parasitisation b y M. demolitor and exposure to virus increased, higher virus doses wer e required to kill parasitised hosts than were required for nonparasit ised hosts of the same age.