HEAT-TRANSFER AND BODY-TEMPERATURE IN HONEY-BEE (HYMENOPTERA, APIDAE) DRONES AND WORKERS

Honey bee, Apis mellifera L., drones and workers were used to examine how differences in morphology, physiology, and behavior affect heat exchange and thorax temperature (T(th)) during flight. Drones had twice the body mass (M(b)) of workers (199.4 +/- 2.5 versus 101.8 +/- 3.3 mg) and exhibited T(th) > 2-degrees-C higher. Drones were unable to lower T(th) through regurgitation or through shunting heat to the abdomen. Heat production during hovering increased with M(b), whereas total heat loss increased with M(b) and with flight speed (V). Despite their larger size and higher T(th), drones flew slower than workers. A heat budget model predicted that T(th) would decrease sharply with V, increase with body mass, and increase with the ratio of thorax mass to body mass. The model closely predicted the T(th) difference between drones and workers and demonstrated that the higher T(th) of drones is primarily (75%) an effect of large M(b), somewhat (15%) a result of the high ratio of thorax to body mass and, to a lesser degree (10%), a result of slower V. These morphological and behavioral traits are sufficient to account for the difference in T(th) between drones and workers.