Bumblebee queens are better at olfactory learning and more sensitive to scents than workers

Intraspecific variation in cognition can reflect ecological demands, yet cognitive performance can be driven by non-cognitive processes. Bumblebees have been a long-standing model in the study of cognition for their aptitude at learning associations, but nearly all research has been limited to one life stage: foraging workers. Queen bumblebees also forage, and previous work shows that they learn visual associations with fewer errors than workers, offering a useful comparison of the drivers of variation in cognition. Here, we tested whether queens' better learning performance holds across another modality: olfaction, and whether performance could be driven by non-cognitive variables related to their larger size including peripheral sensitivity. We first assessed olfactory learning in wild Bombus vosnesenskii and found that queens learned with fewer errors than workers. Following additional training and sensitivity tests, queens and workers did not differ, ruling out non-cognitive variables as driving learning differences in this context. In a second experiment, we tested scent sensitivity under more controlled conditions in Bombus impatiens and found that queens were more sensitive. Our findings confirm learning differences between bumblebee castes and show that queens also have greater peripheral sensitivity, hinting at adaptive drivers of these intraspecific differences.