Laboratory bioassays of the fungus, Verticillum lecanii against different stages of the two cotton bollworms, Earias insulana Boisd. and Pectinophora gossypiella (Saund.) under different concentrations of fungus were studied. The fungus proved virulent efficacy against eggs and larvae of both pests treated eggs of both insect pests caused a reduction rate in the hatchability whereas eggs hatchability was reduced for both insect pests. It was evident that eggs and larvae of both insects were susceptible to fungal infection and most of hatched larvae from treated eggs failed to develop to adults and dead in both E. insulana and P. gossypiella. LC₅₀ values against        E. insulana eggs and larvae were  1.1X10⁷ spores/ml and 1.8X10⁷ spores/ml, respectively; whereas  LC₅₀ values against P. gossypiella eggs and larvae were  1X10⁷ spores/ml and 1.5X10⁷ spores/ml, respectively. Data clarified that P. gossypiella was more susceptible to the fungal than E. insulana through all the tested stages.