Behavioral responses by bumble bees to variation in pollen availability.

Pollen-collecting bumble bees (Bombus spp.) detect differences between individual flowers in pollen availability and alter their behavior to capitalize on rewarding flowers. Specific responses by bees to increased pollen availability included: longer visits to flowers; visits to more flowers within an inflorescence, including an increased frequency of revisits; an increased likelihood of grooming while the bee flow between flowers within the inflorescence; and more protracted inter-flower flights, probably because of longer grooming bouts. The particular suite of responses that a bee adopted depended on the pollen-dispensing mechanism of the plant species involved. Bees buzzed previously-unvisited Dode-catheon flowers longer than empty flowers. In contrast, pollen availability did not significantly affect the duration of visits to Lupinus flowers, which control the amount of pollen that can be removed during a single visit. Simulation results indicate that the observed movement patterns of bumble bees on Lupinus inflorescences would return the most pollen per unit of expended energy. The increased foraging efficiency resulting from facultative responses by bees to variation in pollen availability, especially changes in the frequency and intensity of grooming, could correspondingly decrease pollen dispersal between plants.