Abstract
Eusociality is characterized by division of labor, where specialized roles within a colony are associated with, or driven by, differences in sensory and cognitive abilities. Past research in honeybees ( Apis mellifera ), a species with a strong division of labor, indicates that bees specialized on nectar foraging are less responsive to sucrose than pollen specialists. Whether other social insect species also differ in their sensory responsiveness based on foraging specialization has rarely been addressed and could lend insight into the evolution of these sensory differences. In our first experiment, we investigated sucrose responsiveness in bumblebees ( Bombus spp .), which have smaller colonies with weaker division of labor than honeybees, but where individuals still specialize on foraging tasks in the short-term. Using wild-caught bumblebees ( B. vosnesenskii ), we found that nectar and pollen foragers did not differ in their sucrose responsiveness. Because we could not control for the motivational state of wild foragers, we then repeated the experiment with lab-reared B. impatiens and found the same result. Finally, to confirm that differences found between our bumblebee experiments and past honeybee experiments could not be explained by differences in protocol alone, in our third experiment, we tested wild-caught honeybees using the same protocol and found that, in line with previous work, pollen foragers had lower sucrose response thresholds than nectar foragers. Overall, our results indicate that while honeybee foraging specialization is associated with responsiveness differences, the same is not true for bumblebees, implying that other variables underlie specialization in this genus. Significance statement A central focus of social insect research is understanding what drives division of labor in social insect colonies. The ‘response threshold model’ can explain many behaviors in advanced eusocial insects like honeybees, where individuals with different behavioral roles vary in how responsive they are to task-related stimuli. However, fewer studies have explored whether this model correlates with task specialization in other social insects with weaker divisions of labor, like bumblebees. We tested whether bumblebees specializing on nectar or pollen foraging differed in their sucrose responsiveness and found that they did not, in both wild-caught and lab-reared scenarios. Using the same protocol, we confirmed that wild-caught pollen- and nectar-foraging honeybees differed in sucrose responsiveness. This work strengthens our understanding of the proximate mechanisms driving the division of labor and opens the door to future work on sociality in insects.