UPPER TEMPERATURE TOLERANCE OF 4 SPECIES OF CADDISFLIES (INSECTA, TRICHOPTERA)

Critical Thermal Maximum (CTM) were determined for fifth instar larvae of Hydropsyche simulans Ross and Chimarra obscura (Walker) acclimated to 12, 19 and 26-degrees-C, and Ceratopsyche morosa (Hagen) and Chimarra aterrima Hagen acclimated to 19-degrees-C. The selected CTM endpoint yielded consistent data as the coefficients of variation for all eight species - temperature acclimation combinations were less than 10 %. Mean CTM's ranged from 31.4-degrees-C to 38.5-degrees-C. At the common acclimation temperature of 19-degrees-C, a SNK multiple range test separated the mean CTM's of the four species into two distinct groups: C. obscura = H. simulans > C. aterrima = C. morosa. CTM was directly related to acclimation temperature in both Hydropsyche simulans and Chimarra obscura. The two species representing populations from more northern latitudes (Missouri) had lower CTMs than their congeners or closely related species from more southern latitudes (Texas).