Abstract: The effect of four major parameters, viz., larval age and weight, inoculation dose, incubation temperature and time of harvesting the larvae, on the production of three isolates of nucleopolyhedrovirus of Helicoverpa armigera (HaNPV), viz., Ooty (OTY), Coimbatore (CMB) and Negamum (NGM) were evaluated. Early 5th instar larvae recorded the maximum yield of virus per larva when inoculated with a dose of 5χ105 POB larva‾1 and incubated at a temperature of 25°C. Also, highest POB yield was recorded when virosed larvae were harvested as cadavers. However, among the isolates tested in this study, CMB isolate collected from Tamil Nadu, India, showed the highest yield per larva in all of the conditions.