Laboratory selection, resistance risk assessment, fitness costs and biochemical mechanism of Aphis gossypii to flonicamid

The cotton aphid, Aphis gossypii Glover, one of the most economically destructive pests, causes a significant threat to various crops and has evolved with varying levels of resistance to various types of chemical insecticides. Flonicamid, a novel systemic insecticide, is commonly employed to control sucking insect pests owing to its high efficacy and relatively non-hazardous nature. In this study, the A. gossypii population (F 40 ) exhibited a resistance ratio of 19.68 to flonicamid, with a realized heritability ( h 2 ) of 0.09. F 40 displayed a negative cross-resistance (CR) between flonicamid and several insecticides, such as pirimicarb, acetamiprid and thiamethoxam, while demonstrating minimal CR with lambda-cyhalothrin and bifenthrin. Analysis of the fitness characteristics indicates that the F 40 exhibits a relatively lower fitness of 0.83 and a reduced net reproductive rate when compared to the F 0 strain. The enzyme activity assays suggest that the F 40 strain has a significant increase in activities of cytochrome P450 monooxygenase (P450s) and UDP-glycosyltransferases (UGTs). Furthermore, the F 40 strain exhibits a higher nicotinamidase (NAMase) enzymes activity (1.48-fold) and a significant upregulation of the nicotinamidase gene ( Naam ) expression (2.92-fold) compared to the F 0 strain. Taken together, our results suggest that A. gossypii shows a low propensity for developing resistance to flonicamid and little cross-resistance to typical insecticides. The sustained efficacy of this insecticide could be achieved through strategic rotation or temporary cessation of its use in conjunction with other insecticides. The enhanced activity of P450s, UGTs and NAMase in the F 40 strain may co-contribute to the flonicamid resistance in A. gossypii .