Brain composition and scaling in social bee species differing in body size

We compare four honeybee and one bumblebee species with similar behaviors and ecological requirements but large differences in body size. The bees show allometric brain-body size relationships and scaling exponents similar to those found in vertebrates. Compared with three Asian honeybee species, the European honeybee Apis mellifera feature larger brains than expected for their body mass. Overall, the brains show moderate regional variation across species with two pronounced differences: A. dorsata have an enlarged visual lamina, possibly an adaptation for crepuscular vision. Second, the mushroom bodies are larger and comprise more intrinsic neurons in bumblebees than in honeybees. While these findings might suggest more advanced sensory associations in bumblebees, it is currently not possible to test this notion in the absence of quantitative and comprehensive behavioral comparisons across bee species.