Flight energetics in sphinx moths: heat production and heat loss in Hyles lineata during free flight

Abstract

Mean thoracic temperature of free-flying H. lineata in the field and in the laboratory increased from about 40 °C at T_a= 16 °C to 42·5 °C at T_a = 32°C. At a given T_a, thoracic temperature was independent of body weight and weakly correlated with wing loading. The difference between abdominal temperature and air temperature increased from 2 °C at low T_a to 4·2 °C at high T_a. At a given T_a, the difference between T_ab and T_a was positively correlated with thoracic temperature. Oxygen consumption per unit weight did not appear to vary with T_a from 15 to 30 °C and was inversely proportional to body weight. Thermal conductance of the abdomen (C_ab) was greater than thermal conductance of the thorax (C_th) in still air and at wind velocities up to 2·5 m/s. In moving air at speeds approximating flight, C_th was twice as high as in still air. Under the same conditions C_ab was 3–4 times as high as in still air. Thoracic and abdominal conductance are inversely proportional to their respective weights. These data are consistent with the hypothesis that thoracic temperature is controlled by regulation of heat loss. However, a heat budget derived from these data suggests that heat dissipation may not be sufficient to offset the decrease in passive cooling of the thorax at high ambient temperatures.