Morphometrics, Conductance, Thoracic Temperature, and Flight Energetics of Noctuid and Geometrid Moths

Geometrid moths in our sample differ from noctuid moths in that they have larger wings relative to their body and are smaller in body mass. As a consequence of their smaller mass, thoracic conductance of geometrids is greater than that of noctuids. Wing stroke frequencies increased with body mass and wing loading in both families. Therefore, it is likely that heat production during flight increases with body mass for these moths. Geometrids exhibited similar thoracic temperature excesses (Tth − Ta) of about 5–9 C, regardless of Ta between Ta's of 11 and 22 C. In noctuids, (Tth − Ta) was greater at low Ta than high Ta (12 C at Ta = 11 C; 7 C at Ta = 22 C), suggesting that thermoregulation occurs during flight. Differences in flight performance and thermoregulation were correlated with flight morphology in the two families. Geometrids are capable of immediate flight and are erratic fliers, and high levels of thoracic heat loss coupled with low levels of heat production precluded the possibility of maintaining elevated, regulated thoracic temperatures during flight. In contrast, noctuids have relatively greater rates of heat production due to their wing shape. Compared with the geometrids, the flight pattern of noctuids is energetically more expensive and requires preflight warm-up, but the flight repertoire is enhanced.