CYTOCHROME P450-ASSOCIATED INSECTICIDE RESISTANCE AND THE DEVELOPMENTOF BIOCHEMICAL DIAGNOSTIC ASSAYS IN HELIOTHIS-VIRESCENS

The metabolic enzymes of a multiresistant (i.e., carbamate, organophos phate, pyrethroid) population of tobacco budworm, Heliothis virescens (F.), were compared with those of a susceptible population. The resist ant Hebert population, collected from areas where control failures wit h cypermethrin and thiodicarb had been reported, was selected in the l aboratory with thiodicarb for seven generations. Resistance ratios as determined by topical bioassays were 91- and >150-fold to cypermethrin and thiodicarb, respectively. Resistance-associated increases in meta bolism were found in fifth instar larvae for monooxygenases, carboxyle ster hydrolases, and glutathione transferases. Cytochrome P450 content was elevated in microsomes from gut (3.7-fold), fat body (4.4-fold), and carcass (4-fold). Monooxygenase activity varied substantially amon g the four substrates and three tissue sources examined. For three mon ooxygenase substrates (p-nitroanisole, benzo(a)pyrene, and benzphetami ne) increases in metabolism varied from 3- to 33-fold. The greatest in creases in metabolism were observed with methoxyresorufin, in which in creases were observed in all three tissues (23-, 29-, and 58-fold in f at body, midgut, and carcass microsomes, respectively). Significant in creases ranging from 3- to 5-fold were observed for two esterase subst rates, while smaller differences of up to 2-fold were observed for a g lutathione transferase substrate. The high metabolic activity of the r esistant population suggested that homogenates of individual larvae mi ght be used in resistance monitoring. The development of a monooxygena se-based microtiter plate assay using p-nitroanisole as substrate clea rly discriminates between resistant and susceptible individuals in the third instar, suggesting that biochemical resistance monitoring can b e carried out with field-collected individuals. The esterase substrate p-nitrophenyl acetate also may be a useful tool for resistance monito ring. (C) 1995 Academic Press, Inc.