Body Temperature and Flight Muscle Ratio in the Burrowing Mayfly,Hexagenia bilineata

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Abstract
Hexagenia bilineata, a large-bodied mayfly, provided a convenient model for the study of the physiological ecology of the Ephemeroptera. The thorax temperature (Tth) of free-flying H. bilineata was significantly different from ambient temperature (Ta), but the gradient between them was only about 1° C, which is probably not biologically significant. H. bilineata is clearly ectothermic, and low wing loading may explain the low Tth. H. bilineata emerges during warm and stable weather, when endothermy would provide little advantage. H. bilineata had a very high ratio of flight muscle mass to body mass, which is expected to result from selection pressure on flight performance, yet H. bilineata is a poor flyer. This effect may be a result of freedom from weight constraints.