Heat Production
Most flying insects are incapable of flying in cool climates as the reduced temperature makes it more difficult for enzymes to break down sugar, the fuel for flight. However, bumblebees are capable of flying in temperatures lower than 0˚C due to their ability to increase their thoracic temperature to 30˚C (Heinrich 1979).
Clever Queen Bumblebees - Sir David Attenborough's Life in the Undergrowth. Video provided by BBCworldwide (2008).
A common explanation for the bumblebee’s thermoregulation is the ‘futile cycle’. During bumblebees warming up stage numerous nervous signals are sent to flight muscles but no shivering occurs (Surholt et al. 1991). It is theorised that due to tetanic contraction of the muscle (meaning the muscle can’t move) heat is produced with no movement occurring Staples (2004). Heat is generated by the hydrolysis of ATP (a form of chemical energy) due to the cyclic like conversion of hydrolyse fructose 1-6- biphosphatase to phosphofructokinase Staples (2004). This theory is still questioned today as it has been found that in some bumblebees the futile cycle is insufficient to explain the thorax’s high temperatures Staples (2004).
The conversion of fructose 1-6 biphosphatase (FbPase) to phosphofructokinase (PFK) and the production of the energy (ATP+ H20) that contributes to heat production in bumblebee thorax. Image provided by Staples et al (2004).
Evolution of Thermoregulation in thorax
Bumblebee’s thermoregulation is believed to have evolved as it was needed for the organism to forage for food in cooler climates. In a report by Staples et al. (2004) the level of FbPase was found to decrease with an increase in bumblebee body mass. While the foraging time on flowers increased with increasing body mass. These results suggest that the futile cycle isn’t linked to bumblebee’s thermoregulation for food foraging. Therefore a different unknown pressure for a different unknown mechanism might have resulted in the bumblebee’s thermogenesis (Staples 2004).