Effects of LC25 and LCso fenitrothion and endosulfan on growth, development and re­production of the armyworm Mythimna separata (Walker), surviving the treatment at larval stage, were assayed for the treated and Fi generations of the pest. In the survivors of treated generation, both the insecticides enhanced the developmental durations significantly. Further, endosulfan could reduce significantly the larval, pupal and adult weights, adult longevity and egg production, whereas fenitrothion failed to show any significant effect. On the contrary, fenitrothion increased the egg production significantly. Moreover, both the insecticides demonstrated no influence, either on growth and development or on reproduction of the survivors of Fi generation.