Bumble bees heat up for high quality pollen.

Thermoregulation plays a key role in bee foraging, allowing some species to forage in suboptimal temperatures. Recently, bumble bee thoracic temperature (T(th)) has been shown to increase with nectar carbohydrate content. However, pollen is also vital to bees and exhibits a greater than 20-fold range in protein quality. We provide the first demonstration that bee T(th) is also correlated with pollen quality. We allowed bumble bee, Bombus impatiens, foragers from two colonies to collect pollen varying in quality (25%, 50%, 75% and 100% by mass mixed with indigestible alpha-cellulose). We used infrared thermography to measure surface T(th) when a forager finished collecting feeder pollen and when she returned to the nest. Foragers significantly elevated their T(th) over ambient air temperature while collecting pollen and maintained this elevated T(th) upon returning to the nest. On average, foragers increased T(th) over ambient by 0.4 degrees C per 25% increase in pollen protein content. Bumble bees can therefore adjust their thoracic temperature according to pollen quality.