Possible mechanisms for the formation of flower size preferences by foraging bumblebees

Large flowers often contain larger nectar rewards and receive more pollinator visits than small flowers. We studied possible behavioral mechanisms underlying the formation of flower-size preferences in Bombus terrestris (L.) using a two-phase laboratory experiment. Bumblebees foraged on artificial flowers that bore either a big or a small display of uniform color. Only flowers of one display size contained nectar rewards. We changed the display color and the locations of big and small flowers in the second experimental phase. Forty-one percent of the bees made their first visit to a small flower. Formation of size-reward associations followed a similar course in both experimental phases, reaching >85% choices of rewarding flowers. Some learning occurred within the first three visits. Learning of the size-reward association was equally good for big and small displays in the first experimental phase, but better for small displays in the second phase. Our results suggest that associative learning is involved in the formation of preferences for large displays. Bees that had learned to prefer large displays in one foraging situation may not transfer this preference to a novel situation that is sufficiently different. This behavior may select for honest advertising in flowers.