Pollen odor chemicals as modulators of bumble bee foraging on Rosa rugosa Thunb. (Rosaceae)

Behavioral field studies were conducted to determine if bumble bees ( Bombus terrestris L.) can use pollen odor to assess pollen availability in flowers of Rosa rugosa (Rosaceae), a nectarless species with a distinctive pollen odor. Pollen volatiles were added singly and in mixtures to newly opened flowers from which anthers were removed and were offered to free‐flying bumble bees in an array that included intact flowers as controls. The addition of 2‐tridecanone and geranyl acetate reduced landing responses, but the addition of tetradecyl acetate and especially eugenol significantly increased landing frequency as well as the display of vibratile pollen‐collecting behavior, suggesting that they are key chemicals in a bee’s assessment of pollen availability in individual flowers. Bee responses to flowers in which androecia were exchanged between first‐day flowers (with pollen reward) and second‐day flowers (without pollen reward) provide evidence that bee discrimination between flowers is based mainly on stimuli from the anthers. Overall, the findings show that bumble bees foraging on R. rugosa use primarily pollen odor in concert with visual stimuli from the androecium and secondarily petals odors and colors in selecting rewarding flowers. Controlled pollination and bagging studies indicate that R. rugosa requires cross‐pollination by insects, pointing to the selective advantage that pollen odor provides by increases plant fitness through the enhanced foraging efficiency of bumble bee pollinators.