Entomological Society of America
On-Demand 10-Minute Session
Available Wednesday, November 11, 2020
Click HERE and search for ‘Keaveny’ to access the session on November 11th
How does brood mass and worker number influence brood thermoregulation in the cold?
Bumble bees generate heat with their flight muscles and shunt that heat from the thorax to the abdomen to incubate developing brood. Incubation temperature has been actively researched from the perspective of brood development; however, the thermal dynamic between individual workers and the thermoregulated brood remains surprisingly understudied. Due to its mass and associated thermal inertia, the brood retains heat longer than the comparatively small workers. Therefore, workers would benefit from storing heat in the brood as it provides a thermal resource for subsequent use should they need it. To test this idea, we established Bombus impatiens microcolonies of varying worker quantities and brood sizes. We cooled microcolonies in 5°C increments from 35 to 10°C and monitored air and brood temperatures. We then measured the thermal effect of workers on the brood. Across a four-fold variation in brood size, regulation of brood temperature was determined by number of workers and brood mass. If workers were solely invested in incubating brood, small broods (with higher heat loss) would require continued incubation at cold temperatures; we saw high variation: temperatures of small broods varied as air cooled indicating that workers may not have stayed in contact with the brood. Our findings indicate that the difference between brood temperature with and without workers increases as the number of workers relative to brood mass increases, and when temperatures cool. These findings suggest that worker number relative to brood size is important in brood thermoregulation as temperatures cool though individual behavior warrants further investigation.
Presenting Author: Ellen C. Keaveny
Co-Authors: Michael E. Dillon, PhD