Morphology as a Predictor of Flower Choice by Bumble Bees

This paper examines whether the use of 14 plant species as nectar sources by eight species of bumble bees relates systematically to differences in bee morphology. I predicted that a particular bee should have fed from a given plant species if the bee was physically more similar to the other bees visiting that plant species than to bees on any other species. Glossa (=tongue) length, body mass, and wing length all influence a bumble bee's foraging ability and its choice of flowers and were therefore included in the analysis. Morphological differences between bees were associated with use of different plant species; however, the role of bee morphology in flower choice was most evident when preferred plant species bloomed abundantly. The interaction between morphology and flower choice was also influenced by plant species richness, season, the plant species visited, and the species of bee; but was not affected by the time of day that the bee was foraging, overall bee density, or the bee's caste. Bee species with long glossae had access to nectar in a greater variety of flowers than those with short glossae, and they tended to feed from a larger number of plant species. Also, their use of a particular species was less predictable. Discrimination between bees using different plant species depended on joint consideration of several morphological characters: no character alone accurately separated the bees.