Establishing the nutritional landscape and macronutrient preferences of a major United States rangeland pest, Melanoplus sanguinipes, in field and lab populations

When given a choice, most animals will self-select an optimal blend of nutrients that maximizes growth and reproduction (termed "intake target" or IT). For example, several grasshopper and locust species select a carbohydrate-biased IT, consuming up to double the amount of carbohydrate relative to protein, thereby increasing growth, survival, and migratory capacity. ITs are not static, and there is some evidence they can change through ontogeny, with activity, and in response to environmental factors. However, little research has investigated how these factors influence the relative need for different nutrients and how subsequent shifts in ITs affect the capacity of animals to acquire an optimal diet in nature. In this study, we determined the ITs of 5^th instar (final juvenile stage) Melanoplus sanguinipes (Fabricius, 1798), a prevalent crop and rangeland grasshopper pest in the United States, using two wild populations and one lab colony. We simultaneously collected host plants to determine the nutritional landscapes available to the wild populations and measured the performance of the lab colony on restricted diets. Overall, we found that the diet of the wild populations was more carbohydrate-biased than their lab counterparts, as has been found in other grasshopper species, and that their ITs closely matched their nutritional landscape. However, we also found that M. sanguinipes had the lowest performance metrics when feeding on the highest carbohydrate diets, whereas more balanced diets or protein-rich diets had higher performance metrics. This research may open avenues for studying how management strategies coincide with nutritional physiology to develop low-dose treatments specific to the nutritional landscape for the pest of interest.