Microsomal monooxygenases in diamondback moth larvae resistant to fenvalerate and piperonyl butoxide

Abstract

The microsomal monooxygenase activities toward several model substrates were measured in larval homogenates of strains of diamondback moth exhibiting different levels of fenvalerate resistance, ranging from ca. 300- to > 11,000-fold. Aldrin epoxidase activities varied only <2-fold. Activities of 7-methoxyresorufin O-demethylase, 7-ethoxyresorufin O-deethylase, and 7-ethoxycoumarin O-deethylase were significantly increased in the resistant strains, up to 16-, 5-, and 18-fold, respectively, over those in the susceptible FS strain. 7-Pentoxyresorufin O-depentylase was not detected in any strains. No changes in the sensitivity of these microsomal monooxygenases to in vivo and in vitro inhibition by piperonyl butoxide (PBO) were observed in the strains resistant to PBO, as compared with the FS strain. PBO resistance in diamondback moth was probably also caused by an enhanced microsomal degradation of this synergist.