Abstract |
In laboratory tests, nymphs of Hexagenia bilineata (Ephemeroptera) and larvae of Chironomus crassicaudatus (Diptera) were highly tolerant of short term thermal shocks (six hour duration, simulating entrainment in a thermal plume and drifting to ambient). TL50 values increased from 35C at an acclimation temperature of 5C to 38-40C at an acclimation temperature of 20-25C. However, survivors of these treatments experienced higher percentages of delayed mortality compared to controls after being held for ten days to four weeks at the original acclimation temperature. Field data generated indicated that aquatic insect species inhabiting TVA's large warm-water reservoirs are living close to their thermal maximu, and that an upper limit of 33C would ensure the maintenance of sizeable populations of the species studied. |