Mechanism of acequinocyl resistance and cross-resistance to bifenazate in the two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae)

Acequinocyl and bifenazate are acaricides that inhibit mitochondrial respiratory chain complex III. To analyze acequinocyl resistance mechanisms and cross-resistance risk to bifenazate, we conducted laboratory selection with acequinocyl to a Japanese field population of Tetranychus urticae Koch (Acari: Tetranychidae). Then we characterized resistance traits by examining synergism and maternal inheritance and by DNA sequencing analysis of the target site. Laboratory selection for acequinocyl resistance resulted in 19.8-38.1-fold increases in the resistance factor against a susceptible strain of T. urticae. Selection for bifenazate resistance likewise resulted in a 15.9-37.5-fold increase in the resistance factor. Acequinocyl resistance showed maternal inheritance and strong synergism with piperonyl butoxide (PBO), a cytochrome P450s inhibitor. Target site (mitochondrial cytochrome b) sequencing demonstrated the substitution of an amino acid residue, G126S. These results indicate that target site mutation and detoxification by cytochrome P450 play essential roles in acequinocyl resistance. In contrast, maternal effects were not clearly detected in bifenazate susceptibility of F-1 females from reciprocal crosses between acequinocyl-resistant and -susceptible strains. Therefore, G126S is unlikely to be a major resistance factor for decreased bifenazate susceptibility in the acequinocyl-resistant strain. Significant synergistic effects of PBO indicate that cytochrome P450 genes selected by acequinocyl likely confer cross-resistance against bifenazate.