Genetics of esterase-mediated insecticide resistance in the aphid Schizaphis graminum

Abstract

The genetics of organophosphate resistance, including the pattern of inheritance and the underlying genetic mechanism, were investigated in the aphid Schizaphis graminum (the greenbug). Resistant greenbugs with pattern 1 (R1) and pattern 2 (R2) esterase and susceptible (S) greenbugs were induced into the sexual cycle and crossed. Each resistance-associated esterase pattern in the greenbug was inherited in a Mendelian fashion as a single gene. An aphid clone that displayed both resistance-associated esterase patterns was produced in the F1 generation of a cross between R2 and R1 insects, and was designated pattern 3 (R3). DNA from different R1 aphids and the R3 aphid clone displayed a restriction fragment pattern different from that of R2 and S clones, and about a twofold increase in hybridization compared with S aphids. DNA from R2 clones showed no restriction fragment differences or increased hybridization signal compared to S insects. These findings suggest that the mechanism behind the R1 esterase activity may be gene amplification, but that the R2 elevated esterase activity may result from a different genetic mechanism.