Does size matter? Bumblebee behaviour and the pollination of Cytisus scoparius L. (Fabaceae)

The effects of forager body size and floral display size on pollinator beha viour were assessed in a relatively specialised plant-pollinator system. Cy tisus scoparius, which has structurally complex, nectarless flowers is poll inated by foraging bumblebees. Variations in bee body size affected the pro portion of open flowers visited, the ability of bees to trigger the pollina tion mechanism of flowers and handling times on open flowers. Smaller bees handled flowers more successfully and efficiently than larger ones. Contrar y to previous reports, all bees preferred to visit open flowers and possibl e explanations for this are discussed. Floral display size also affected be haviour as bees visited more flowers per plant on larger plants, but visite d a lower proportion of the available flowers. There was no interaction bet ween body size and floral display size, suggesting that bees of all sizes r espond in a similar manner to variations in floral display sizes. The poten tial impacts of variations in bumblebee behaviour on plant reproductive suc cess are discussed.