BUMBLE BEE-INITIATED VIBRATION RELEASE MECHANISM OF RHODODENDRON POLLEN

Although Rhododendron spp. anthers have apical pores and should be exp ected to be buzz pollinated, bees do not normally sonicate them to rel ease pollen. Stamens were examined to determine their pollen release m echanism; the filaments were shown to have natural vibration modes tha t cause pollen to be forcibly ejected by vibration, providing the poll en is mature. The first natural vibration mode of the stamens was foun d to generate centrifugal force sufficient to throw the pollen toward the apical pore and out of the anther, so that it adheres to the anthe r tip and hangs in the bee's path to the nectaries. These vibrations m ay be triggered by bees brushing past the long stamens when foraging f or nectar, so that the flowers retain their pollen until insect vector s begin foraging on them. The low frequency vibration modes of the vis cin threads, which hold the pollen together, may contribute towards th e pollen ejection by low frequency stamen vibration. Vibration transmi ssion of dehiscent anthers containing pollen was good from 50 Hz to 85 0 Hz, suggesting that sonication should be an efficient method of poll en collection, although this rarely occurs. Vibratory ejection occurs at a constant energy level, rather than the constant force levels foun d in previous research on Actinidia.