Modeling Differences in Insect Developmental times between Constant and Fluctuating Temperatures

Abstract

Developmental time data collected at constant temperatures poorly predicted developmental times of red flour beetle, Tribolium castaneum (Herbst), and 16 other species at fluctuating temperatures over a broad range of mean temperatures or amplitudes of fluctuating temperatures. Developmental times at constant temperatures tended to be shorter above 25-30°C temperature range and longer below this range, than at fluctuating temperatures with the same means. Differences between developmental times at constant temperatures and those at fluctuating temperatures also tended to increase with the amplitude of fluctuating temperatures. Different methods were compared for predicting insect developmental times at fluctuating temperatures. One method made predictions by integrating constant temperature developmental time data over the 24-h fluctuating temperature cycle. This adjusts for the nonlinear relationship between temperature and developmental time. After making this adjustment, predictions were >40% closer on average to observed developmental times at fluctuating temperatures. With developmental time data collected at fluctuating temperatures, temperature-development equations can be fitted over a broader range of temperatures above and below those favorable for survival of insects at constant temperatures. When these equations were used to do integration, predictions of developmental times at fluctuating temperatures were even better, improving by ≈70%. Improvement may be a result partially of consideration of both the means and amplitudes of fluctuating temperatures in predicting developmental times. These methods provide an alternative to degree-day accumulation method for prediction of developmental times at fluctuating temperatures in the field.