IMMUNOLOGICAL DETECTION OF GREENBUG (SCHIZAPHIS-GRAMINUM) ESTERASES ASSOCIATED WITH RESISTANCE TO ORGANOPHOSPHATE INSECTICIDES

Organophosphate resistance in the geeenbug, Schizaphis graminum, has b een at least partially attributed to two distinct patterns of nonspeci fic esterase isozymes (Type I and II). Antiserum raised against a puri fied Type II esterase was specific for this enzyme and did not cross-r eact with the Type I esterase, indicating that the two greenbug estera ses are immunologically distinct. The antiserum reacted identically wi th the Type II esterase in both resistant and susceptible insects base d on both immunoblots and quantitative immunoelectrophoresis despite t he much higher activity of this isozyme associated with the resistant strain. These results indicate that the isozyme is immunologically ind istinguishable in resistant and susceptible insects and that the resis tance appears to involve a modification of the enzyme rather than over expression. These results contrast with those obtained for the Type I esterase, which gave a strong reaction with an antiserum against the E 4 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 l ikely to involve a mechanism resulting in overexpression of the enzyme . (C) 1997 Academic Press.