Abstract: To investigate the resistance level of Helicoverpa armigera (Hübner) from transgenic Bt cotton field to insecticides and ascertain their biochemical mechanisms, three field populations were collected in 2011 and 2012 from southern suburbs of Baoding, Nanpi County of Cangzhou and Julu County of Xingtai in Hebei Province, North China. The toxicity of eight insecticides was tested by topical application method, and the activities of the related carboxylesterase (CarE), glutathione S-transferases (GSTs) and acetylcholinesterase (AChE) were determined by biochemical analysis. The results showed that the three field populations had medium- or high-level resistance to betacypermethrin and fenvalerate (the R/S ratio: 20.02-73.70), low- or medium-level resistance to methomyl ( the R/S ratio: 6.27-11.84), but were sensitive to lambda-cyhalothrin (the R/S ratio: 1.07-4.20), phoxim, chlorpyrifos and malathion (the R/S ratio: 1.00-2.69), and chlorantraniliprole (the R/S ratio: 2.00-3.67). The activities of CarE, GSTs and AChE in the three field populations were 1.06-1.23, 1.20-1.63 and 1.15-1.23-fold as high as that in the susceptible population, respectively, and this may be correlated with the resistance to betacypermethrin, fenvalerate and methomyl.

Key words: Helicoverpa armigera, transgenic Bt cotton, insecticide resistance, insecticide, resistance ratio, enzyme activity