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 (Spodop tera eridania Cram.) larvae for three days, the effect on total conten t and activities of cytochrome P450 and on insecticide toxicity were d etermined. Both 2,4-D and atrazine induced cytochrome P450-catalyzed a ldrin epoxidation (AE) and methoxyresorufin O-demethylation (MROD). Th e 2,4-D was a more potent inducer for total cytochrome P450 content, w hereas atrazine disproportionately increased AE. Both compounds increa sed MROD significantly. The apparent kinetic characteristics of AE ind icates 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-i nduced cytochrome P450 caused decreased parathion and permethrin toxic ity. The carbaryl toxicity correlated directly with 2,4-D-induced tota l P450 content and activities but not with atrazine-induced changes. T he 2,4-D and atrazine also induced nonspecific esterase activity which may contribute to permethrin detoxification.