Leaves of 120 DAP Bt cotton were less toxic to T.
ni larvae. When the first instars continuously fed on 120 DAP Bt cotton leaves, 75.9, 60.6, 56.4 and 38.4% of larvae
survived to second, third, fourth and fifth instars respectively, and 20.9% pupated and 17.9% successfully became
adults. However, it took the surviving first instars 37.1 days to become adults, which was 7.2 and 8.9 days longer
than those fed on 50 and 120 DAP non-Bt cottons respectively. Pupae that developed from larvae that fed on 120
DAP Bt cotton leaves were only 50.9 and 52.6% of the weight of those developed from larvae that fed on 50 and
120 DAP non-Bt cotton respectively. Non-Bt cotton, both 50 and 120 DAP, did not exhibit significant effects on
larval survival and development, except that the pupae in the 50 DAP non-Bt cotton treatments developed over a
significantly longer time than those in the 120 DAP non-Bt cotton treatment.