Temperature regulation of the sphinx moth, Manduca sexta. I. Flight energetics and body temperature during free and tethered flight.

The sphinx moth, Celerio lineata, is thought to vary the rate of heat production in response to different rates of heat loss (Heath & Adams, 1965, 1967). It was proposed that during flight in cold air the attitude of the wings is changed, resulting in increased 'drag', greater flight effort, and greater rates of heat production (Adams, 1969). However, direct evidence has not been presented to substantiate this or other hypotheses of how moths may regulate their body temperature during flight. Energy expenditure during flight is related to wing-loading (Weis-Fogh, 1964), and heat production is a by-product of muscular effort. On the basis of wing-loading, the minimum energy expenditure and heat production would be less during suspended than during free flight, and thoracic temperature {TTh) should, therefore, also be lower. However, if during flight heat is produced for temperature regulation, TTh should be the same in tethered as in free flight. In other words, if flight effort and heat production are separate phenomena, then it should be possible to separate them experimentally. In these studies an attempt is made to clarify the relationship between the heat production which is a by-product of flight effort, and the heat production which might be independent from this.