Honey bee workers as mobile insulating units

Summary.

Heat-shielding is a method used by honey bee workers to insulate temperature sensitive brood from localized heat stress during development. Due largely to data collection techniques, heat-shielding has been defined as stationary bees congregating with their ventral side facing the heat stress. We conducted tests to determine if shielding behavior was limited to bees fitting this description. Specifically, we examined the behavior in response to heat and cold stress, and recorded both stationary and moving workers on the hive wall (ventral side visible) and on the brood comb (dorsal side visible). Our observations strongly suggest that stationary bees on the brood comb shield the developing brood from both localized heat and cold stress: after temperature-stress, the number of bees under the stressor significantly increased. A uniform response from stationary bees on the hive wall, however, was not observed: stationary bee number increased significantly after heat stress but tended to decrease after cold stress. Movement of bees on both the hive wall and brood comb decreased in response to cold stress. Movement of bees on brood comb decreased after heat stress, whereas the movement of bees on the hive wall increased in response to heat stress. This latter result raises the possibility that these bees are creating currents used to dissipate the heat and/ or are absorbing heat near the source and moving it to nonsensitive areas. Our data indicate that ‘heat-shielding’, as previously defined, is a category within a broader response of honey bees to localized temperature stress: Apis mellifera appear to respond adaptively to all localized temperature stressors.