Meeting Abstract
98.5 Monday, Jan. 6 14:30 The effects of food macronutrient content on an insect herbivore: a fitness landscape approach. LE GALL, M.*; BEHMER, S.T.; Texas A&M University; Texas A&M University le-marron@tamu.edu
The plants that insect herbivores eat can be highly variable with respect to their protein and digestible carbohydrate content. Here we explore the effects of protein-carbohydrate balance and concentration in the generalist grasshopper Melanoplus differentialis by conducting two separate experiments. In the first we presented last instar nymphs with two foods that differed in their nutrient content, and measured the extent to which individuals actively regulated their intake. In the second we presented insects with one of nine foods that differed in their protein-carbohydrate ratio and/or amount, and measured consumption, performance and nutrient utilization. For this second experiment, the results are presented as detailed fitness landscape. This visualization technique provides a comprehensive overview of how nutrient content affects an insect herbivore, and a powerful link between lab and field studies. In the first experiment we found that grasshoppers tightly regulated their protein intake across all treatments. However, when the available foods had low total nutrient content, carbohydrate intake decreased; these insects also gained less mass. In the second, where insects were constrained to one of nine foods, grasshoppers initially consumed larger quantities of carbohydrate-biased food. Over the entire stadium, however, insects on the most dilute diet ate the most food. Development time decreased as macronutrient concentration increased, but mass gain and growth rate was best on diets that were: 1) concentrated and 2) carbohydrate-biased. Interestingly, food utilization, measured as the amount of food digested, was best on diets with low protein and moderate carbohydrate content. We interpret our results in relation to the protein-carbohydrate landscape occupied by insect herbivores in the field.
