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, th e physiological consequences of this behavior are poorly understood. I n this study, we investigate thermal effects on feeding, digestion, an d net energy intake for Melanoplus bivittatus, the two-striped grassho pper In the field, M, bivittatus maintained body temperatures (T-b's) between 32 degrees C and 38 degrees C throughout most of a sunny day, but T-b's dropped to 0 degrees -15 degrees C at night. The threshold T -b for feeding in the field was 25 degrees C but was 15 degrees C when grasshoppers were kept without food for 12 h at 35 degrees C. Variabl es determined by the ability of the digestive tract to process food (f ood intake and fecal production per 8 h) were more temperature sensiti ve (Q(10)'s of 4-5) than variables reflecting chewing and crop-filling rates (Q(10)'s of 2-2.5). Higher T-b strongly increases net energy in take primarily by increasing digestive tract throughput in M. bivittat us, augmenting rates of individual development opment, and population expansion. The grasshopper's digestive system was essentially nonfunct ional during half of its normal day in the field, implying that adapta tion to high T-b's constrains digestive function at low T-b's.