Mixed-Function Oxidase and Glutathione S-Transferase Activities from Field-Collected Larval and Adult Tobacco Budworms, Heliothis-Virescens (F.)

Abstract

Mixed-function oxidase and glutathione S-transferase activities were measured from tissue homogenates of larval and adult tobacco budworms that were collected from cotton fields in Texas and Louisiana. Mixed-function oxidase activity toward p-nitroanisole was detected in both developmental stages and, in six of the eight field collections tested, mean levels of activity were significantly higher than activity measured in parallel assays with insects from a laboratory-reared, insecticide-susceptible colony. However, the significance of this activity with respect to pyrethroid metabolism and resistance is unclear because variation in mixed-function oxidase activity among these strains was poorly correlated with susceptibility to cypermethrin. Glutathione S-transferase activities toward 3,4-dichloronitrobenzene and 1-chloro-2,4-dinitrobenzene were also detected in both larvae and adult insects, and mean levels varied among the field collections tested. Patterns of activity in tissues examined for both mixed-function oxidases and glutathione S-transferases were different between larvae and adults suggesting that the regulation and expression of these enzyme activities is dependent on developmental stage.