The energetic cost of hovering flight was measured in sphinx moths from five species. Mean power input per unit mass (Pi/M) varied from 237–2 W kg-1 in Manduca sexta (Subfamily:Sphinginae), mean body mass 1-2 X 10(−3) kg, to 327-9 W kg-1 in Deilephila elpenor (Subfamily: Macroglossinae) mean body mass 7-3 X 10(−4) kg. Mean Pi/M for the five species was inversely proportional to mean body mass and directly proportional to mean wing loading. For any given body mass, Pi/M was greater in Hyles lineata than in M. sexta. This difference is correlated with higher wing loading at any given mass in H. lineata. Energy expenditure per unit mass of thorax was 1018 W kg-1 in H. lineata and 694 W kg-1 in M. sexta. Within each of these species, Pi per unit mass of thorax does not vary with body mass. Power input data are compared with calculated power requirements based on momentum theory and blade-element theory of helicopter aerodynamics. Absolute efficiency, the ratio between calculated power requirements and measured energy expenditure, appears to vary directly with body mass. These data provide an energetic basis for observed correlates between thoracic temperature and flight effort in flying sphinx moths.

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