Toxicological significance of enzyme activities in profenofos-resistant tobacco budworms, Heliothis virescens (F.)

Resistance to profenofos and activities of enzymes associated with metabolism of organophosphorus insecticides were measured in larvae of the tobacco budworm, Heliothis virescens (F.), that were field-collected from Louisiana during the 1995 cotton growing season. High frequencies of profenofos resistance were recorded in all field-collected strains and were strongly correlated with esterase activity and moderately correlated with glutathione S-transferase activity toward 1-chloro-2,4-dinitrobenzene. Mean levels of acetylcholinesterase sensitivity to inhibition by chlorpyrifos oxon were lower in some field strains than that of an insecticide-susceptible strain: however, acetylcholinesterase sensitivity and resistance were poorly correlated in all field strains. Finally, there was no correlation between resistance and activities of P450-monooxygenase toward p-nitroanisole or glutathione S-transferase toward 1,2-dichloro-4-nitrobenzene. These results suggest possible contributions of both metabolic and target site mechanisms toward profenofos resistance in this insect. (C) 1997 Academic Press.