In-vivo effects of 2,4-D and atrazine on cytochrome P-450 and insecticide toxicity in southern armyworm (Spodoptera eridania) larvae

After feeding 2,4-D or atrazine in a diet to southern armyworm (Spodoptera eridania Cram.) larvae for three days, the effect on total content and activities of cytochrome P450 and on insecticide toxicity were determined. Both 2,4-D and atrazine induced cytochrome P450-catalyzed aldrin epoxidation (AE) and methoxyresorufin O-demethylation (MROD). The 2,4-D was a more potent inducer for total cytochrome P450 content, whereas atrazine disproportionately increased AE. Both compounds increased MROD significantly. The apparent kinetic characteristics of AE indicates that 2,4-D and atrazine induced similar P450 isozymes (K-m 8.78 and 7.80 mu M, respectively), which may differ from the constitutive isozyme (K-m 3.14 mu M). The 2,4-D-induced cytochrome P450 contributed to decreased carbaryl and permethrin toxicity, whereas the atrazine-induced cytochrome P450 caused decreased parathion and permethrin toxicity. The carbaryl toxicity correlated directly with 2,4-D-induced total P450 content and activities but not with atrazine-induced changes. The 2,4-D and atrazine also induced nonspecific esterase activity which may contribute to permethrin detoxification.