TEMPERATURE-DEPENDENT FEEDING RATES OF MELANOPLUS-SANGUINIPES NYMPHS (ORTHOPTERA, ACRIDIDAE) IN LABORATORY TRIALS

Feeding rates of laboratory-reared Melanoplus sanguinipes (F.) nymphs were measured in 3-h trials at 15, 20, 26, 30, 35, 40, or 45 degrees C. Feeding rates increased with temperature to a maximum, then decreased at higher temperatures. Maximum feeding rate occurred at 35 degrees C in Ist and 2nd instars, and at 40 degrees C in 3rd, 4th, and 5th instars. In a subsequent 24-h trial, mean hourly feeding rates at 30, 35, or 40 degrees C agreed with those of the 3-h trials. A linear model was used to describe feeding rates at temperatures at or below that at which rate was maximum, and a nonlinear model was used to describe the feeding rate trends over the full range of experimental temperatures. Using the linear model, estimated low-temperature feeding thresholds ranged from 13.5 degrees C for 2nd instars to 15.9 degrees C for Ist instars. Using the nonlinear model, estimated low-temperature feeding thresholds were near 13 degrees C for all but 3rd instars, for which it was near 8 degrees C; modeled temperatures at which feeding was maximal agreed with measured values, and the modeled upper temperature threshold for feeding was between 45 and 46 degrees C for all instars. The linear and nonlinear models are similar at temperatures below that at which feeding is maximal, but the linear model overestimates feeding at higher temperatures. Application of the feeding rate functions to held conditions requires improved understanding on the determinants of body temperature under held conditions, and on the relationship between feeding and wastage.