Large interspecific differences in redox potential exist among herbivorous lepidopteran larvae. Reducing conditions occur in the midguts of Manduca sexta (Sphingidae) and Polia latex (Noctuidae), whereas oxidizing conditions prevail in the midguts of Lymantria dispar (Lymantriidae), Danaus plexippus (Danaidae), and Papilio glaucus (Papilionidae). The epithelium of the posterior midgut of M. sexta fed a diet containing bismuth subnitrate accumulates bismuth sulfide, suggesting that sulfide might be one of the reducing agents responsible for the maintenance of reducing conditions in this species. We propose that the effects of plant allelochemicals in insect herbivores will be strongly affected by gut redox conditions and that the regulation of gut redox conditions is an important adaptation of insect herbivores to the chemical defenses of plants. The redox state of the gut is yet another insect trait that must be included in the analysis of plant-insect interactions.
