Thermoregulation in bumblebees

Summary

• 1. The rates at which the beesBombus vosnesenskii warmed up (Fig. 1) and expended energy depended strongly on their thoracic temperature.

• 2. Queens of bothB. vosnesenskii andB. edwardsii regulated their thoracic temperature at 36 to 45° C during free flight at 2 to 35° C (Figs. 3 and 4).

• 3. The ability of the smaller bees (workers) to thermoregulate in continuous flight appeared to be limited to the higher ambient temperatures (Fig. 4), and they usually did not remain in continuous free flight at ambient temperatures <10°C.

• 4. Thoracic temperature (Fig. 5) and energy expenditure during free flight (Fig. 7) were correlated with the weight of the abdomen, as affected by honeystomach contents.

• 5. Abdominal temperature remained near ambient temperature during warm-up (Fig. 2), and during free flight at low ambient temperatures (Fig. 3). During free flight at high ambient temperatures, on the other hand, the temperature of the abdomen approached that of the thorax.

• 6. Body temperatures during free flight differed from those previously observed during foraging, during brood incubation and during tethered flight. Interrelationships between thoracic and abdominal temperature are discussed in terms of energy expenditure.