Abstract: 【Aim】 Aphis gossypii is easy to produce resistance to insecticides because of its short growth cycle and high reproduction rate. This study aims to clarify the levels and mechanisms of imidacloprid resistance in A. gossypii in the main cotton production areas of China. 【Methods】 Different populations of A. gossypii were collected from fields in Haidian of Beijing (BJ), Langfang (LF) and Handan (HD) of Hebei, Dezhou (DZ) of Shandong, Xuchang (XC) of Henan, and Kuitun (KT) and Akesu (AKS) of Xinjiang. Leaf-dipping method was used to determine the resistance levels of A. gossypii to imidacloprid. The activities of three detoxification enzymes ［mixed function oxidase (MFO), carboxylesterase (CarE) and glutathione S-transferase (GST)］ and acetylcholinesterase (AchE) in different A. gossypii populations were assayed. And the mutation of target gene (nAChR β1 subunit gene) was also detected. 【Results】 The BJ, XC and HD populations of A. gossypii were still susceptible to imidacloprid, while the LF, AKS, DZ and KT populations exhibited moderate levels of resistance to imidacloprid, with the resistance ratios of 22.6-, 26.3-, 53.5- and 61.1-fold, respectively. The activities of MFO, CarE and GST in the AKS and KT populations were significantly higher than those in the BJ susceptible population. The activities of MFO, CarE and GST in the AKS population were 1.7-, 1.6- and 1.5-fold, and those in the KT population were 1.8-, 1.7- and 1.5-fold as high as those in the BJ population, respectively. But there was no significant difference in acetylcholinesterase (AchE) activities among the AKS, KT and BJ populations. A single point mutation in the nAChR β1 subunit causing an arginine to threonine substitution (R81T) observed in LF, AKS, DZ and KT populations was associated with the imidacloprid resistance in A. gossypii. 【Conclusion】 The results suggest that enhancement of MFO, CarE and GST activities and the mutation (R81T) of nAChR β1 subunit might confer resistance to imidacloprid in A. gossypii.

Key words: Aphis gossypii, imidacloprid, resistance, resistance monitoring, enzyme activity, nAChR β1 subunit