Mechanisms of Body-Temperature Regulation in Honeybees, Apis Mellifera

Abstract

Honeybees when endothermically heated maintained an elevated head temperature (T_H). During free flight at 17 °C T_H was approximately 7 °C above ambient temperature (T_A). However, during flight at T_A near 46 °C, head temperature averaged 3 °C below T_A. When tethered bees were heated on the head till T_H reached 46 °C, they regurgitated nectar from their honeycrop, held it on their ‘tongue’, and initiated violent aortic pulsations in the head and in–out movements of the nectar droplet. Temperature changes in the head corresponded with heart pulsations. Head temperature was prevented from rising and was stabilized. The heart pulsations in the abdomen and aortic pulsations in the head (and abdominal ventilatory movements) were often synchronous, but during heating of the head they were often independent of each other in both frequency and amplitude. The fluid droplet was several degrees Centigrade below head, thoracic and ambient temperatures, and it remained in motion in and out of the body. It caused T_H to be 4–8 °C lower, by the resulting evaporative cooling, than is possible without the droplet. It is concluded that at low T_A the elevation and regulation of T_Th automatically results in the elevation of T_H. However, at low T_H heat flows from the heated thorax to the head, not only by passive conduction but also by physiologically facilitated blood circulation.