Antioxidants in grasshoppers: Higher levels defend the midgut tissues of a polyphagous species than a graminivorous species

Polyphagous grasshoppers consume plants that contain markedly greater amounts of potentially prooxidant allelochemicals than the grasses eaten by graminivorous grasshoppers. Therefore, levels of antioxidant defenses maintained by these herbivores might be expected to differ in accordance with host plant ranges. Antioxidant levels were compared in midgut tissues and gut fluids of a polyphagous grasshopper, Melanoplus sanguinipes, and a graminivorous grasshopper, Aulocara ellioti. Glutathione concentrations in midgut tissues of M. sanguinipes (10.6 mM) are among the highest measured in animal tissues and are twice as high as those in A. ellioti. alpha-Tocopherol levels are 126% higher in midgut tissues of M. sanguinipes than in those of A. ellioti, and remain at high levels when M. sanguinipes is reared on plants containing a wide range of alpha-tocopherol concentrations. Ascorbate levels in M. sanguinipes midgut tissues are 27% higher than in those of A. ellioti, but vary depending on the host plant on which they are reared. Midgut fluids of both species contain elevated levels of glutathione, as well as large ( millimolar) amounts of undetermined antioxidants that are produced in the insects. The consumption of tannic acid decreases ascorbate concentrations in midgut tisssues and gut fluids of A. ellioti but has no effect on ascorbate levels in M. sanguinipes. The results of this study provide the first measurements of antioxidants in grasshoppers and suggest that the maintenance of high levels of antioxidants in the midgut tissues of polyphagous grasshoppers might effectively protect them from oxidative stress.