Abstract:In order to monitor the frequency of resistance of the cotton bollworm Helicoverpa armigera (Hübner) field population to Bt cotton in Xinjiang, isofemale lines of cotton bollworm were collected from two different localities in Xinjiang in 2010-2011. Subsequent offspring was screened with Cry1Ac artificial diet, and the resistant individual of cotton bollworm population was detected using F1/F2 screening method. A total of 123 isofemale lines from Shihezi were assayed in 2010, and 152 isofemale lines from Shache in 2011. None of the relative average developmental rating of individual for conferring resistance to Bt cotton was higher than or equal to 0.8 in two areas. It has been estimated that the frequency of resistance of the cotton bollworm field population were under 10-3 in both Shihezi and Shache. Relative average development rating of F1 larvae had significant differences with that of its F2 offspring from Shache. The results showed that the resistance frequency of cotton bollworm field population was still at the sensitive level in Shihezi area, and the tolerance of the cotton bollworm field population in Kashgar area, however, increased a little.