Resistance Evaluation of Bt Transgenic Cotton to Cotton Bollworm, Helicoverpa armigera, in mid-Changjiang River Valley

Resistance of two Bt transgenic cotton lines (GK 19 and BG 1560) to cotton bollworm (Helicoverpa armigera) was assessed through bioassay and field investigation. The research results indicated that there were significant differences of resistance levels among various organs and developmental stages of both Bt transgenic cotton lines by bioassay. In general, resistance level of reproduction organs were higher than leaves in two lines, and it decreased gradually as cotton growth from July to September;The field trial showed that control efficiencies to the third and fourth generations of cotton bollworm on GK 19 and BG 1560 were 86.21% and 87.89%, 93.10% and 92.19%,respectively, while peak densities were 14 and 28 larvae per hundred plants in conventional cotton field. It is suggested that both GK 19 and BG 1560 possess high potential for control of cotton bollworm in cotton planting area alone mid Changjiang River Valley.