IN-VITRO METABOLISM OF PARATHION IN SUSCEPTIBLE AND PARATHION-RESISTANT STRAINS OF THE GREENBUG, SCHIZAPHIS-GRAMINUM (RONDANI) (HOMOPTERA, APHIDIDAE)

Results of in vitro metabolism studies in a susceptible and two parath ion-resistant greenbug strains indicate that hydrolytic enzymes are ac tive toward paraoxon, but not parathion, and are partially responsible for resistance. The resistance does not involve reduced levels of oxi dative metabolism and activation of parathion since NADPH-dependent mi crosomal formation of paraoxon in resistant and susceptible strains wa s similar. Paraoxon is a potent inhibitor of greenbug esterases, and t he resistance mechanism apparently involves rapid and tight binding of enzyme and insecticide that prevents the insecticide from reaching it s target site. Native polyacrylamide gel electrophoresis also supporte d this view since staining of enhanced bands associated with resistanc e was inhibited by incubation with paraoxon. The resistant strains app arently produce more of the isozymes that are inhibited by paraoxon an d are able to sequester a greater number of paraoxon molecules than su sceptible greenbugs. (C) 1994 Academic Press, Inc.