Cross-resistance And Mechanism Of Imidacloprid-resistant Aphis Gossypii Glover (Homoptera: Aphididae) To Neonicotinoid Insesticides

In order to confirm the cross-resistance to neonicotinoid insecticides, resistance mechanism and biological characteristics of imidacloprid-resistant cotton aphid, and to guide the rational use of neonicotinoid insecticides, the dipping method, microspot method, biochemical method and systematic observation method were adopted with the strains of the imidacloprid-resistant population, the xiajin population and the susceptible population. The trends of resistance development were researched, at the same time the cross-resistance to neonicotinoid insecticides, resistance mechanism and biological characteristics of imidacloprid-resistant cotton aphid were investigated. The results were as follows:1. The resistance level of A. gossypii to imidacloprid reached to medium resistance with 41.7-fold after selection of 45 generation with the pressure to kill 60% to 70% individuals of the population. The resistance of A. gossypii to imidacloprid increased slowly at the first 9 generations, and then increased rapidly from the 12th to the 36th genatation, at last the resistance increased slowly again from the 36th to the 45th genatation. The level of resistance will continue to development if the selection is kept on. When the resistance ratios reached to 38.2-fold, the resistance stability of A. gossypii to imidacloprid was determined. The resistance reduced rapidly in the first 8 generation, and the resistance gradually kept steady to 14.4-fold after 14 generation. The imidacloprid-resistant cotton aphid of 14.4-fold was selected over again, the resistance of A. gossypii increased rapidly, and the resistance increased to 40.3-fold after 9 genetarions.2. Based on LC50 values, the toxicity ratios of nitenpyram, acetamiprid and thiacloprid were 5.78-, 4.52- and 3.68-fold, respectively, suggesting cross-resistance between imidacloprid and these neonicotinoids. However, there was no cross-resistance existed between imidacloprid and three neonicotinoid insecticides including clothianidin, thiamethoxam and dinotefuran.3. The biochemical results showed that dinotefuran could significantly inhibit the CarE, GST and AChE of the imidacloprid-resistant population, with the inhibition of 64.01%, 49.31% and 36.30% respectively. Dinotefuran also showed obvious inhibition on the CarE, GST and AChE of the Xiajin multi-resistant population, with the inhibition of 32.39%, 32.47% and 26.45%. Nitenpyram showed little effect on the CarE, GST and AChE of the imidacloprid-resistant population, with the inhibition of 18.00%, 5.71% and 18.28%. TPP and PBO had obvious effect on the synergy to imidacloprid and nitenpyram, with the synergism ratio of 2.32- and 2.98-fold of imadacloprid, while little effect on the synergy to dinotefuran, with the synergism ratio of 1.31- and 1.67-fold. DEM showed no obvious synergism to the three insecticides with the synergism ratio of 1.07-fold.4. In the study of sublethal effects, imidacloprid at LC20 doses could suppress weight gain and honeydew excretion, with the inhibition of 43.7% and 23.4%, resprcitively, but showed no significant effects on longevity and fecundity of the imidacloprid-resistant cotton aphid. However, other neonicotinoid insecticides showed significant adverse effects on biological characteristics (body weight, honeydew excretion, longevity and fecundity) in the order of dinotefuran > thiamethoxam and clothianidin > nitenpyram > thiacloprid and acetamiprid.