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‐demethylatin (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 μM, respectively), which may differ from the constitutive isozyme (K_m 3.14 μM). 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.