Comparative Study of Chill-Coma Temperatures and Muscle Potentials in Insect Flight Muscles

Muscle potentials in insect flight muscles decrease in amplitude and increase in duration with decreasing temperature. Amplitudes fall to zero at distinct temperatures, which are characteristic for different species. Chill-coma temperature is thus defined here as the critical temperature below which flight muscles cannot be activated. Chill-coma temperatures were 2°C in the species of butterflies measured and −2 to 0°C in the moths. In the species of Hymenoptera, Coleoptera and Diptera measured, chill-coma temperatures ranged from 3 to 14°C. The rate of decline of muscle potential amplitudes with decreasing temperature was different for different species. Rates were smaller over most of the temperature range for species that warm up from low environmental temperatures to reach thoracic temperatures necessary for flight. Amplitudes decreased faster at higher thoracic temperatures in species that start shivering only at higher ambient temperatures. Temperature has a similar effect on durations of muscle potentials in different species. Between 25 and 15°C, durations increased by 100% in all species. The results suggest that cold-adaptation is not strongly related to chill-coma temperature but is strongly related to the rate of decline of muscle potential amplitudes.