Preflight warm-up rates and flight temperatures are strongly determined by body mass (Stone and Willmer 1989b). Heat loss is proportional to surface area and MHP is proportional to thoracic volume, with the result that at small body sizes convective heat loss predominates. In small insects endo-thermic abilities do not necessarily imply stable body temperatures. It is common for Tth to be elevated by endothermy during flight but not regulated, as in gypsy moths Lymantria dispar (Lyman-triidae) in which Tth in free flight remains 6-7°C above Ta (Casey 1980). This species has a body mass of approximately 100 mg and the wings are large, so power requirements for flight are low and immediate flight is possible without preflight warm-up. From comparative data on moths of different families it is apparent that differences in metabolism, flight performance and the extent of thermoregulation are largely determined by morphometries (for noctuids and geometrids see Casey and Joos 1983).
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