Abstract
The critical thermal maximum (CTmax) of Pteronarcys dorsata (Say) acclimated in the laaboratory to 5 different temperatures ranging from 4 to 28 degrees C was 34.7-36.6 degrees C. A 6th temperature (33 degrees C) resulted in 100% mortality during the acclimation period. Although its CTmax values rank P. dorsata as moderately sensitive to thermal stress, the <2 degrees C difference over a 7-fold increase in acclimation temperature suggests only a weak ability to adapt to warming conditions relative to other tested aquatic insect species. This stenothermy in P. dorsata was likely due to the consistently cool stream in which this populations lives. Our results suggest that cold-water populations are particularly susceptible to thermal alterations. They also provide the first CTmax values for a species of pteronarcyd stonefly and the first of any aquatic insect over such a wide range of acclimation temperatures.