WOODS JR., William A. *; HEINRICH, Bernd; STEVENSON, R. D. ; University of Massachusetts Boston; University of Vermont; University of Massachusetts Boston: Honeybee Flight Energetics: Flying in the Light of Day

Several recent sets of respirometry measurements of flying bees have, in disagreement with earlier work, supported the conclusion that the honeybee A. mellifera and other bee species regulate thorax temperature during flight by controlling heat production. In an effort to account for these differing results, we made open-flow respirometry measurements of honeybees flying in a 500 cc glass chamber at air temperatures ranging from 22 to 40 °C. In initial indoor measurements, 7 of 8 bees repeatedly extended their feet and attempted to land, and were kept flying only by frequent agitation of the chamber. After we moved the apparatus outdoors, 30 of 51 bees maintained flight with infrequent or no agitation, making few or no landing attempts; 14 required agitation to maintain flight and 7 showed mixed behavior. For bees in non-agitated flight, CO₂ production was independent of air temperature (n=31, r²=0.01, P=0.55). In contrast, for bees in agitated flight CO₂ production decreased as air temperature increased (n=21, r²=0.61, P<0.0001), with values at 38 °C less than 2/3 those at 22 °C. Though our results might seem to suggest that control of heat production during flight is an artifact of agitation, some studies supporting this mechanism employed little or no agitation. The salient difference in our study was the presence of nearly natural visual stimuli; foraging bees have been shown to orient themselves using polarized light and familiar landmarks, and to judge distance by motion parallax. We conclude that providing visual stimuli more closely approaching those found in nature may be more important than previously recognized for resolving this and other insect flight energetics questions.