Dependence of flight on temperature regulation in the moth, Manduca sexta.

Some insects markedly increase their internal temperature during flight. Locusts (Church, i960) maintain an internal thoracic temperature 6 °C in excess of the ambient temperature. The sphinx moth Celerio lineata raises its temperature to a minimum level before take-off, and during flight it maintains an internal temperature within a range of 4 °C independent of the external temperature (Adams & Heath, 1964). The regulation of thoracic temperature presumably optimizes the responsiveness of the flight system as well as allowing the moth independence of ambient temperature for its active periods. Large moths use two distinct patterns of flight muscle activity in thermoregulation, flight and a special warm-up pattern. Celerio and other insects (Adams & Heath, 1964; Dorsett, 1962; Dotterweich, 1928; Rammer, 1967; Krogh & Zeuthen, 1941; Moran & Ewer, 1966; Soltavalta, 1954) vibrate their wings through a small angle until the muscular activity has raised the temperature of the thorax, and then, take off. Most investigators who have studied warm-up behaviour distinguish it from flight activity by the small amplitude of the stroke and the rising thoracic temperature. Our study of Manduca sexta investigates the effects of ambient temperature upon the flight system during both flight and warm-up and the internal temperature regulation exhibited behaviourally and during muscular activity by this moth. Finally, we propose a general model for heat balance in endothermic insects.