GENETICS OF ESTERASE-MEDIATED INSECTICIDE RESISTANCE IN THE APHID SCHIZAPHIS-GRAMINUM

The genetics of organophosphate resistance, including the pattern of i nheritance 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) greenb ugs were induced into the sexual cycle and crossed. Each resistance-as sociated esterase pattern in the greenbug was inherited in a Mendelian fashion as a single gene. An aphid clone that displayed both resistan ce-associated esterase patterns was produced in the F-1 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 restri ction fragment pattern different from that of R2 and S clones, and abo ut a twofold increase in hybridization compared with S aphids. DNA fro m R2 clones showed no restriction fragment differences or increased hy bridization signal compared to S insects. These findings suggest that the mechanism behind the R1 esterase activity may be gene amplificatio n, but that the R2 elevated esterase activity may result from a differ ent genetic mechanism.