Heat Transfer and Body Temperature in Honey Bee (Hymenoptera: Apidae) Drones and Workers

Abstract

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°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 h , 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.