Does dietary P affect feeding and performance in the mixed-feeding grasshopper (Acrididae) Melanoplus bivitattus?

Although consequences of limited dietary protein and carbohydrate to performance are well studied for terrestrial insect herbivores, the importance of phosphorus (P) remains poorly understood. We examined the significance of dietary P to performance in fifth-instar nymphs of the grasshopper Melanoplus bivittatus fed artificial diets. Consumption, digestion, developmental rate, and growth in response to different levels of P nested within standard-Protein and carbohydrate diets were determined. Developmental rate was slowest on high-P diets; protein:carbohydrate concentration and P in diets affected frass production and consumption. Approximate digestibility and conversion of digested food were primarily influenced by the protein:carbohydrate quality of the diet but not P. Mass gain was marginally lower in the low-Protein:high carbohydrate diet used in this study. At the individual level, other than small effects to developmental rate at high concentrations for M. bivittatus, dietary P otherwise seems to have little effect on nymphal performance. To the degree that it is important, effects of dietary P depend on the concentrations of protein and carbohydrate in the diet.