Resistance detection and synergism of enzyme inhibitors on neonicotinoids to Aphis gossypii in Shandong Province

In order to survey the resistance level of cotton aphid(Aphis gossypii Glover) to neonicotinoids in Shandong Province, the sensitivity of three field populations collected from Liaocheng, Tai'an and Dongying and one susceptible population to 6 neonicotinoids (imidacloprid, nitenpyram, acetamiprid, thamethoxam, thiacloprid, and clothianidin) was determined by capillary micro-topical application method. The synergisms of three enzyme inhibitors(TPP, DEM and PBO) on the toxicity of six neonicotinoids to A.gossypii were also measured. The results showed that Tai'an population of A.gossypii exhibited medium level of resistance to nitenpyram, with resistance ratio of 16.95-fold; low level of resistance to imidacloprid and acetamiprid, with resistance ratio of 5.69- and 9.57-fold, respectively; but no resistance to clothianidin, thamethoxam and thiacloprid, with resistance ratio less than 3.0-fold. Liaocheng population of A.gossypii exhibited medium level of resistance to imidacloprid, acetamiprid and thamethoxam, with resistance ratio of 28.51-, 25.88- and 18.16-fold, respectively; and low level of resistance to thiacloprid and clothianidin, with resistance ratio of 6.01- and 6.37-fold, respectively; but still sensitive to nitenpyram. Dongying polulation of A.gossypii exhibited medium level of resistance to imidacloprid, acetamiprid and clothianidin, with resistance ratio of 37.95-, 21.52- and 12.95-fold, respectively; and low level of resistance to clothianidin, nitenpyram and thamethoxam, with resistance ratio ranged from 4.75- to 7.07-fold. Enzyme inhibitor PBO and TPP had significant synergism on the 6 neonicotinoids; DEM also showed synergism to some extent. In conclusion, the results of present study suggested that the field populations of cotton aphid collected from three areas of Shandong province developed different level of resistance to the six neonicotinoids tested; the detoxification of mixed-functional oxidase (MFO), carboxylesterase (CarE) might play a key role in the resistance; glutathione-S-transferase (GST) might also make a certain contribution to the resisitance