In vivo penetration and metabolism of methyl parathion in larvae of the tobacco budworm, Heliothis virescens (F.), fed different host plants

Abstract

The effect of wild tomato, Lycopersicon hirsutum f. glabratum (accession PI 134417), and peppermint, Mentha piperita L., on the susceptibility, penetration, and metabolism of methyl parathion, O,O-dimethyl O- p-nitrophenyl phosphorothioate, was studied in larvae of the tobacco budworm, Heliothis virescens F. Third-instar larvae fed wild tomato or peppermint leaves for 1 day were 3.3- and 2.7-fold more tolerant to methyl parathion, respectively, as compared to insects fed an artificial diet. These tolerance levels were only 2.2- and 1.7-fold, respectively, in fifth-instar larvae when fed leaves of the same plant species for 1 day. Penetration studies did not indicate any differences in the rate of penetration of methyl parathion in larvae fed different diets. Methyl parathion injected into fifth-instar larvae was converted into three chloroform-soluble and five water-soluble metabolites. Five hours after injection, the extent of methyl parathion metabolism was greater in larvae fed wild tomato leaves (77.4%) or peppermint leaves (72.8%), than in those fed an artificial diet (64.55%). The major metabolite was p-nitrophenol and its formation was higher in larvae fed wild tomato leaves (49.4%) than in larvae fed peppermint leaves (44.23%), which in turn were higher than those fed an artificial diet (38.19%). These data suggested that the two plants induced enzymes responsible for detoxifying methyl parathion.