Rates of development of Melanoplus sanguinipes F. from Alaska were determined at eight constant temperatures between 21 and 42°C. Diurnally alternating temperatures were used to estimate rates of development at temperatures too low for nymphs to complete development under constant temperatures. Two previously published equations were fit to these data and used to predict developmental rates as a function of temperature. The first equation, nonlinear and only approaching zero rate of development asymptotically, was fit to the data from constant and alternating temperature treatments. The second equation, which included an intercept, was fit to the data from constant temperature treatments only. Estimated developmental times based on these equations were tested against observed developmental times in two fluctuating temperature regimes in growth chambers, and two seasons of field sampling. Elevation of body temperature of grasshoppers above ambient temperatures in the field was modeled as a linear function of solar irradiance, based on field measurements. The effect of behavioral thermoregulation on nymphal developmental times in the field was estimated using standard air temperatures and solar-adjusted temperatures. Rates of development under most of the constant temperature treatments were higher than any previously published for M. sanguinipes. Estimated rates of development in the field using air temperatures only were about one-half those using solar-adjusted temperatures. Observed developmental times in the field were 45 and 42 d in 2000 and 2002, respectively. Because of local adaptation and behavioral thermoregulation, duration of nymphal stages in M. sanguinipes is relatively independent of latitude.