Nuclear Polyhedrosis Virus (NPV) is host specific for Spodoptera litura and Helicoverpa armigera. NPV is a stomach poison. NPV is effective when it is ingested by the larvae. The mass production of NPV of H. armigera and S. litura is same except H. armigera is reared in individual vial to avoid cannibalism. The NPV of these pests can be produced by using both natural as well as artificial diet contaminated with the respective NPV. The third instar larvae of these pests either collected from field or reared in the laboratory are allowed to feed the contaminated diet. Keep larvae hungry for 24 hours before inoculation of virus. Larvae get infected with virus within 3-4 days and hang themself upside down in tubes. These infected larvae are collected in a beaker containing water for 3-4 days for putrification. The putrified larvae are crushed with the help of mixer cum grinder by adding some water. This solution is filtered with the help of muslin cloth and add more water, if required. The filtered extract solution is centrifuged (30,000 RPM) to separate the polyhedral of NPV from the solution. The polyhedral is separated from the water and is ready to use.