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Survival and fertility characteristics of the third instar larvae of Spodoptera litura (Fabricius), on Bt-I and Bt-II cotton hybrids during 120-150 DAS were assessed in the laboratory. Life tables and population parameters of the S.litura were constructed in an environment with unlimited food supply and that was free of natural enemies. The results revealed that the modest rate of mortality occurred in the immature stage, especially in the third instar. The population parameters calculated are recorded as low in Bt-II hybrids compared to Bt-I hybrids. The net reproductive rate (R 0 ) recorded highest 447.24 on NCS-954 Bt-I whereas lowest on RCH-134 Bt-II as 169.35 with the mean generation time (Tc) 40.01 days. Intrinsic rate of increase (r m ) was ranged from 0.12-0.18, the highest r m was recorded on Bt-I hybrids. The population doubling time (DT) was 5.39 days on RCH-134 Bt-II. The Bt-II hybrids have shown a profound impact on the growth and development of S.litura during early stages of crop, as the crop matured the Cry toxin content decreased, survival rate recorded was more in 4 th and 5 th instar larvae in later stages of crop.` K e y w o r d s

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