HARRISON, J.F.*; WOODS, H.A.; FAY, M.L.; PERKINS, M.C.; Arizona State University, Tempe; Univ. of Texas, Austin; Arizona State University, Tempe; Orange Coast College, Costa Mesa: Is phosphate an important nutrient influencing the growth, physiology and behavior of herbivorous insects, or a generally overabundant micronutrient?

Studies of the nutritional ecology of herbivorous insects have focused on nitrogen and energy as key nutrients. However, stoichiometric theories developed for freshwater aquatic systems predict that phosphate (P) should also be an important nutrient limiting growth of herbivorous insects. We tested these predictions using two insects that represent distinct lineages and feeding strategies: the tobacco hornworm, Manduca sexta, and the American locust, Schistocerca americana. For both species, variation in dietary P levels in the range of those occurring in nature strongly affected growth rates. Manduca sexta responded to variation in dietary P by varying excretion rates, apparently by altering net transport in the renal system. Manduca also accumulated P as a-glycerophosphate when fed diets high in P. Schistocerca were able to preferentially consume diets high in P when provided with visual and olfactory/gustatory cues. Together these data strongly suggest that P is an important nutrient influencing growth, physiology and behavior of a wide variety of herbivorous insects.