Study on Damage of Helicoverpa armigera to Transgenic Bt Cotton and Its Control Index

The yield loss of transgenic Bt cotton caused by cotton bollworm (Helicove rpa armigera) and control index of this insect in coastal cotton area of J iangsu province were studied through inoculation experiment. The results indicat ed that the number of remnant bollworm, rate of injured bud and boll, and yield loss all increased as the number of inoculated bollworm increased; the correlati on between the number of remnant bollworm and the number of inoculated bollworm was logarithmic in the second generation, while it was linear in the third and fourth generation; the control index of bollworm in the second, third and fourt h generation was 15, 8 and 10 heads of 3 instar larvae per 100 plants respective ly, or 1.18%, 2.70% and 3.30% of injured bud and boll respectively. 