PHYSIOLOGICAL AND DIETARY INFLUENCES ON MIDGUT REDOX CONDITIONS IN GENERALIST LEPIDOPTERAN LARVAE

We examined the effects of host plant foliage and redox active compoun ds on the midgut physicochemistry of several species of lepidopteran l arvae. Midgut pH varied among Helicoverpa tea, Heliothis virescens, Ps eudoplusia includens and Hyphantria cunea but was not affected by the host plant they fed upon (cotton, clover, wild geranium or soybean). H owever, redox potential was influenced by both plant and lepidopteran species, Midgut redox potentials closely matched the redox potential o f foliage homogenized under alkaline, but not neutral pH, suggesting t hat alkalinity has a strong influence on the reducing strength of foli age in the gut lumen, Artificial diet containing redox active compound s, including thiol reducing agents and plant allelochemicals, signific antly lowered midgut redox potential of H, tea when ingested, Juglone induced a 205% drop in redox potential in the lumen, whereas caffeic a cid, chlorogenic acid, pyruvate, cysteine, dithiothreitol and ascorbic acid had more moderate effects (34-44% reduction), Quebracho, tannic acid, o-coumaric and p-coumaric acids had no significant effects, Thes e findings suggest that much of the variation in midgut redox conditio ns observed in folivorous caterpillars is due to the redox activity of host plant chemicals at the alkaline pH of the gut.