To Forage or Not: Responses of Bees to the Presence of Other Bees on Flowers

Information on responses of flower-foraging bees to the presence of other visitors simultaneously using the same resource is essential in further understanding bee decision-making processes during the collection of floral rewards. An individual must evaluate the relative costs of exploiting an occupied resource versus moving on to another resource. We investigated responses of foraging individuals to the presence of conspecifics or heterospecifics in three field experiments with solitary and social bees visiting flowers of wild strawberry, Rubus hirsutus Thunb. (Rosaceae). The proportion of Micrandrena spp. that occupied flowers after meeting other foragers was significantly lower than the proportions of Osmia orientalis Benoist and Apis mellifera L. Moreover, the avoidance response of Micrandrena spp. when approaching dead bees (“artificial” visitors) was stronger than that of the other bee species. We also placed an artificial visitor on flowers and observed subsequent responses of natural visitors. The responses of foraging bees to the presence of other visitors varies among species; O. orientalis more frequently visited flowers on which dead Micrandrena spp. were placed than flowers on which dead bees of other species were deployed. Both A. mellifera and Micrandrena spp. avoided flowers on which any other bees were set. We propose that O. orientalis makes decisions on whether to visit an occupied flower after discriminating between flower occupant species by body size.