D3293: Role of sensory response thresholds in bumble bee foraging specialization

A defining characteristic of eusociality is division of labor, where individuals have specialized roles within a colony. These roles can be associated with, or even driven by, differences in sensory and cognitive abilities. For example, honeybee (Apis sp.) foragers that specialize on nectar have higher sucrose response thresholds than pollen foragers, making them more selective in the nectar they collect. Bumblebee (Bombus sp.) foragers do not exclusively forage for a single resource like honeybees, but still show task specialization over shorter durations. However, it is unclear whether these shorter-term specializations are related to differences in sensory thresholds. We tested this with wild-caught bumblebees of four species foraging for pollen or nectar. We offered bees increasing concentrations of sucrose and recorded proboscis extension as a measure of sucrose acceptance. Contrary to findings from honeybees, nectar-foraging bumblebees were more likely to respond to lower concentrations of sucrose than pollen foragers. These differences may reflect variation between honeybees and bumblebees in their degree of division of labor. We are now following up with a lab-based study to determine whether we observe similar response thresholds in more controlled conditions.