Laboratory bioassay studies revealed that nuclear polyhedrosis virus Infection, in late stage larvae of Heliothis armigera and Spodoptera litura increased their susceptibility to insecticides. The virus infection increased the susceptibility of final instar larvae of H. armigera to fenvalerate, cypermethrin, endosulfan and monocrotophos. The enhanced susceptibility was maximum in cypermethrin followed by endosulfan. The susceptlblllty of final instar larvae of S. litura to fenvalerate, cypermethrin, endosulfan, phenthoate and chlorpyriphos was also substantially increased.