Instantaneous oxygen consumption and muscle stroke work in Malacosoma americanum during pre-flight warm-up

Instantaneous rates of oxygen consumption , thoracic temperature (Tth) and wing stroke frequency (n) were continuously measured at several ambient temperatures (T2) during pre-flight warm-up and subsequent cooling in a small volume (30 ml), open flow (240–300 ml min−1) respirometer. Heat production (HP) was tightly coupled to Tth and independent of T2. The rate of change of HP (mWmin−1) was directly related to T2. Total cost of warm-up was strongly, inversely related to Ta. The energetic cost of cooling was a small fraction of the total cost of warm-up. Increased energy expenditure occurred as a result of increases in both n and stroke work input. The latter increased from 0·58 to 1·1 mJ stroke−1 at low Tth (13–25°C) and was essentially constant at higher Tth (25–40°C). Wing stroke frequency increased continuously and linearly with Tth. In contrast to previous estimates based on heat exchange analyses, stroke work during warm-up was equivalent to values measured during free hovering flight. These data are consistent with the hypothesis that energy expenditure is maximized during warm-up.