Temperature Regulation of the Sphinx Moth, Manduca Sexta

1. The sphinx moth, Manduca sexta, maintained an average thoracic temperature of 40-42 °C during free flight in ambient temperatures (TA) of about 16-33 °C. In the extremes, the excess of thoracic temperature TTh over TA varied from a mean of 25 °C at 12.5 °C, to a mean of 8 °C at a TA of 35 °C. 2. During tethered flight TTh increased directly with TA, and the excess of TTh over TA varied from about 11-4 °C. 3. The oxygen consumption was about 45-50 C.C. O2/g h during free flight from ambient temperatures of 15-30 °C. During captive flight the oxygen consumption was about 21 c.c. O2/g h. 4. The wing-beat frequency and amplitude during both free flight and captive flight did not vary significantly with TA. The wing-beat frequency was about the same during free flight and captive flight but the wing-beat amplitude was significantly less in the latter. 5. The moths showed little variation of flight speed with respect to TA on the flight mill. The difference between TTh and TA was strongly correlated with flight speed at low, but not at high, TA. 6. The cooling rate of dead moths was only slightly correlated with air speeds from 2 to 5 m/s. 7. The cooling rate of thoraces without scales was 2.4 times as great as with scales intact at an air flow 2 m/s, but the cooling rate of the abdomen was only slightly increased after the removal of its scales. 8. The data suggest that the rate of metabolism during flight is altered with regard to the flight effort, but not with regard to temperature-regulation. Heat is actively dissipated from the thorax during flight at high TA, or during fast flight when TTh reaches 40 °C or above.