Thermal Effects on Feeding Behavior and Net Energy Intake in a Grasshopper Experiencing Large Diurnal Fluctuations in Body Temperature

Behavioral thermoregulation is well documented in insects; however, the physiological consequences of this behavior are poorly understood. In this study, we investigate thermal effects on feeding, digestion, and net energy intake for Melanoplus bivittatus, the two-striped grasshopper. In the field, M. bivittatus maintained body temperatures (Tb's) between 32° C and 38° C throughout most of a sunny day, but Tb's dropped to 0° - 15° C at night. The threshold Tb for feeding in the field was 25°C but was 15° C when grasshoppers were kept without food for 12 h at 35° C. Variables determined by the ability of the digestive tract to process food (food intake and fecal production per 8 h) were more temperature sensitive (Q10's of 4-5) than variables reflecting chewing and crop-filling rates (Q10's of 2-2.5). Higher Tb strongly increases net energy intake primarily by increasing digestive tract throughput in M. bivittatus, augmenting rates of individual development, and population expansion. The grasshopper's digestive system was essentially nonfunctional during half of its normal day in the field, implying that adaptation to high Tb's constrains digestive function at low Tb's.