The Resistance of Three Helicoverpa armigera Populations to Four Insecticides before and after Transgenic Bt Cotton Planting

In order to monitor the developmental tendency of resistance of Helicoverpa armigera(Hübner) to four insecticides,three H.armigera populations were collected from Taian, Xiajin in Shandong Province and Tianmen in Hubei Province in 1990,1992,2001 and 2005, respectively. The resistance was measured by the topical application of the 4th instar larvae.The bioassay results showed that the resistance of the three populations to fenvalerate presented a drastic increase from 1990 to 1992(13.256.1-folds),a gently increase from 1992 to 2001(3.1～11.0-folds) and a decline from 2001 to 2005.There were similar tendency of resistance to methomy and phoxim,but the resistance level was low.The three populations to endosulfan were susceptible.The change of resistance was associated with the using frequency of insecticides and the large-scale Bt cotton cultivation.