Printed in Great Britain MECHANISMS OF BODY-TEMPERATURE REGULATION IN HONEYBEES, APIS MELLIFERA I. REGULATION OF HEAD TEMPERATURE

1. Honeybees when endothermically heated maintained an elevated head temperature (TH). During free flight at 17 °C TH was approximately 7 °C above ambient temperature (TA). However, during flight at TA near 46 °C, head temperature averaged 3 °C below TA. 2. When tethered bees were heated on the head till TH 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. 3. 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. 4. 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 TH to be 4-8 °C lower, by the resulting evaporative cooling, than is possible without the droplet. 5. It is concluded that at low TA the elevation and regulation of TTh automatically results in the elevation of TH. However, at low TH heat flows from the heated thorax to the head, not only by passive conduction but also by physiologically facilitated blood circulation