Biochemical Mechanisms and Diagnostic Microassays for Pyrethroid, Carbamate, and Organophosphate Insecticide Resistance/Cross-Resistance in the Tobacco Budworm,Heliothis virescens

Abstract

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 susceptible laboratory population. Selection of this Macon Ridge population with thiodicarb on cotton increased resistance for thiodicarb to 172.9-fold and resulted in cross-resistance for cypermethrin to 161.3-fold compared to the susceptible control. Thiodicarb-selected Macon Ridge budworms were also resistant to methyl parathion (7.6-fold), profenofos (59.9-fold), and azinphosmethyl (>38.8-fold). Cytochrome P450 metabolism ofp-nitroanisole was elevated 30.1-, 16.8-, and 18.8-fold in midgut, fat body, and carcass, respectively, of the selected Macon Ridge budworms. The P450 content was also increased. Ester hydrolysis of 1-naphthyl acetate andp-nitrophenyl acetate as well as 1-chloro-2,4-dinitrobenzene and 1,2-dichloro-4-nitrobenzene glutathioneS-transferase activity were elevated approximately 2-fold with some variability among the specific tissues examined. Piperonyl butoxide increased thiodicarb toxicity by 14.8-fold, methyl parathion by 9.3-fold, and cypermethrin by 19.4-fold.S,S,S-Tributylphosphorothioate increased thiodicarb toxicity by 14.5-fold, methyl parathion by 6.6-fold, and profenofos by 7.2-fold. These results suggests that both cytochrome P450 and esterase play an important role in tobacco budworm resistance and cross-resistance between carbamates, organophosphates, and pyrethroids. Acetylthiocholine hydrolysis was 3.4- and 3.5-fold insensitive to paraoxon and methomyl, respectively, in the thiodicarb-selected Macon Ridge strain. Microassays based onp-nitroanisole andp-nitrophenyl acetate metabolism were successfully used to diagnose resistance in field populations of the tobacco budworm in different geographical areas of the U.S.