Immunological Detection of Greenbug (Schizaphis graminum) Esterases Associated with Resistance to Organophosphate Insecticides

Abstract

Organophosphate resistance in the greenbug,Schizaphis graminum,has been at least partially attributed to two distinct patterns of nonspecific esterase isozymes (Type I and II). Antiserum raised against a purified Type II esterase was specific for this enzyme and did not cross-react with the Type I esterase, indicating that the two greenbug esterases are immunologically distinct. The antiserum reacted identically with the Type II esterase in both resistant and susceptible insects based on both immunoblots and quantitative immunoelectrophoresis despite the much higher activity of this isozyme associated with the resistant strain. These results indicate that the isozyme is immunologically indistinguishable in resistant and susceptible insects and that the resistance appears to involve a modification of the enzyme rather than overexpression. These results contrast with those obtained for the Type I esterase, which gave a strong reaction with an antiserum against the E4 esterase associated with resistance in the green peach aphid,Myzus persicae.Western blot analysis indicated that the Type I esterase is present at much higher levels than in the susceptible insects and is likely to involve a mechanism resulting in overexpression of the enzyme.