Metabolism and penetration of permethrin in resistant and susceptible strains of tobacco budworm, Heliothis virescens (F)

Abstract

A laboratory selected strain of Heliothis virescens demonstrating a 400-fold resistance to permethrin exhibited no differences in penetration and only a slight enhancement of metabolism when compared with a susceptible strain. Synergism with piperonyl butoxide and DEF produced similar synergist ratios for the resistant and susceptible strains, but the resistant strain showed a much larger synergist difference. Thin layer chromatography of extracts from larvae dosed with 14C-labelled permethrin demonstrated a small increase in metabolism of the cis-isomer by the resistant strain, but no differences in metabolism of the trans-isomer. The synergism study and the 14C-labelled permethrin experiment both indicate that there is a small increase in metabolism of permethrin in the resistant strain, but not enough to account for the greatly increased LD50 value. Cross-resistance to DDT indicated that target site insensitivity may play a major role in resistance to pyrethroids in this strain.