BIOCHEMICAL-MECHANISMS AND DIAGNOSTIC MICROASSAYS FOR PYRETHROID, CARBAMATE, AND ORGANOPHOSPHATE INSECTICIDE RESISTANCE CROSS-RESISTANCE INTHE TOBACCO BUDWORM, HELIOTHIS-VIRESCENS/

Tobacco budworm, Heliothis virescens, larvae were collected from wild velvet leaf in Macon Ridge (LA) where insecticide resistance in cotton was previously reported. The initial resistance levels were 58.0-fold for thiodicarb and 16.0-fold for cypermethrin compared to a susceptib le laboratory population. Selection of this Macon Ridge population wit h thiodicarb on cotton increased resistance for thiodicarb to 172.9-fo ld and resulted in cross-resistance for cypermethrin to 161.3-fold com pared to the susceptible control. Thiodicarb-selected Macon Ridge budw orms were also resistant to methyl parathion (7.6-fold), profenofos (5 9.9-fold), and azinphosmethyl (>38.8-fold). Cytochrome P450 metabolism of p-nitroanisole was elevated 30.1-, 16.8-, and 18.8-fold in midgut, fat body, and carcass, respectively, of the selected Macon Ridge budw orms. The P450 content was also increased. Ester hydrolysis of 1-napht hyl acetate and p-nitrophenyl acetate as well as 1-chloro-2,4-dinitrob enzene and 1,2-dichloro-4-nitrobenzene glutathione S-transferase activ ity were elevated approximately 2-fold with some variability among the specific tissues examined. Piperonyl butoxide increased thiodicarb to xicity by 14.8-fold, methyl parathion by 9.3-fold, and cypermethrin by 19.4-fold. S,S,S-Tributylphosphorothioate increased thiodicarb toxici ty by 14.5-fold, methyl parathion by 6.6-fold, and profenofos by 7.2-f old, These results suggests that both cytochrome P450 and esterase pla y an important role in tobacco budworm resistance and cross-resistance between carbamates, organophosphates, and pyrethroids. Acetylthiochol ine hydrolysis was 3.4- and 3.5-fold insensitive to paraoxon and metho myl, respectively, in the thiodicarb-selected Macon Ridge strain. Micr oassays based on p-nitroanisole and p-nitrophenyl acetate metabolism w ere successfully used to diagnose resistance in field populations of t he tobacco budworm in different geographical areas of the U.S. (C) 199 6 Academic Press.