Metabolism of ring- and methoxy-14C-labeled fenitrothion was examined in the organo-phosphorus-resistant and -susceptible strains of rice stem borer larvae. Major metabolites of fenitrothion in both strains were fenitroxon, dimethyl phosphorothioate dimethyl phosphate, 3-methyl-4-nitrophenol and 3-methyl-4-nitrophenyl β -D-glucoside, and minor metabolites were desmethyl compounds and oxidative products of the 3-methyl group on the phenyl ring. Penetration rates of fenitrothion into the larvae were almost equal in the two strains, while detoxication rates and fenitroxon levels were significantly different. Fenitroxon levels were 2 to 72 times higher in the susceptible strain, while the levels of dimethyl phosphate, a hydrolysis product of fenitroxon, were from 5 to 20 times higher in the resistant strain. The results indicate that increased detoxication of fenitroxon by cleaving the P(O)-O-aryl bond is the principal mechanism of fenitrothion resistance in the resistant strain.
ASJC Scopus subject areas
- Insect Science
- Health, Toxicology and Mutagenesis