Microsomal oxidase and glutathione transferase as factors influencing the effects of pulegone in southern and fall armyworm larvae

Abstract

The mint monoterpene pulegone and one of its oxidation products, menthofuran, are 3.5–4 times more toxic, acutely, to southern armyworm, Spodoptera eridania (Cramer) than to fall armyworm, S. frugiperda (J. E. Smith) larvae. When the insects are exposed to these compounds in the diet, over an extended period of time, the reverse is true. The southern armyworm larvae have higher cytochrome P-450 content and activities in midgut and fatbody tissues than the fall armyworm larvae. Glutathione transferase activities are comparable in midgut tissues of the two species, but higher in fatbodies of the fall armyworm than of the southern. Pulegone induces cytochrome P-450 activities in both species including its own oxidation as indicated by pulegone-dependent NADPH oxidation. When the insects are stressed with pulegone or menthofuran as in the present study, the observed differences in metabolic activities in the two species may be factors influencing the observed acute and chronic toxicities in each case.