Abstract: Systematic investigations in an experimental cotton field showed stable resistance of GK19, a cultivar of transgenic Bt cotton, to the cotton bollworm, Helicoverpa armigera (Hübner). The experiment included three treatments. The first was a transgenic Bt cotton plot that used pesticides to control pests, the second was a Bt cotton plot that relied on natural enemies to control pests, and the third was a routine cotton plot that adopted IPM (integrated pest management) to control pests. Cotton bollworm populations in the transgenic Bt cotton plots were controlled at very low levels with the maximal density being 12 per 100 cotton plants, even if no pesticides was sprayed throughout their growth stage. Bioassay in the laboratory showed that the weights of 6th instars larvae and pupae from the colony reared on the Bt cotton were 25.6% and 18.2% less respectively compared to those raised on routine cotton. Cotton bollworms that fed on Bt cotton grew slower and their generation duration was at least 17 days longer than those that fed on nonBt cotton. This resulted In reduced damage to transgenic Bt cotton plants.

Key words: Transgenic Bt cotton, cotton bollworm, resistance, spatial and temporal pattern