Abstract: Susceptible bioassay base line and discrimination doses for biopesticide Bacillus thuringiensis (Bt) on susceptible strain (SUS1) of Helicoerpa arrnigera(Huibner) with the diet infection method were established. The susceptibilities to commercial Bt subspecies kurstaki formulation in newly hatched larvae of H. arrnigera collected from six counties of five provinces were tested in 1995. The results indicated that the five populations of H. armigera from Yanggu (Shandong), Handan (Hebei), Xinxiang (Henan), Xiaoxian (Anhui) and Fengxian (Jiangsu) showed early resistance to Bt.The proportion of resistant individuals in this insect at the 5 locations was 5%-10%;LC₅₀ values increased slightly but the slope (b) decreased significantly as compared with those of susceptible strain. However, Dongtai population (Jiangsu) was still susceptible. The biopesticide Bt resistance of H. armigera was diagnosed for the first time. The effects of trangsgenic cotton lines expressing Bt toxin on various populations of H.Armigera with foliage-feeding method were also determined. The results indicated the average mortality of newly hatched larvae of H. armigera (Yanggu and Xinxiang) with early resistance to Bt declined significantly (about 16%-29%) compared with those of susceptible strain. It's suggested that populations of H. armigera from Yanggu and Xinxiang were resistant to biopesticide Bt and transgenic cotton expressing Bt toxin.The resistant management strategy of biopesticide Bt is discussed.

Key words: Helicoverpa armigera, biopesticide Bt, resistance transgenic cotton