THE FLORAL BIOLOGY OF MELASPHAERULA (IRIDACEAE: CROCOIDEAE): IS THIS MONOTYPIC GENUS POLLINATED BY MARCH FLIES (DIPTERA: BIBIONIDAE)?

摘要

Bibio longirostris, a small (ca. 5 mm long) nectar-feeding fly (proboscis ca. 1 mm long) was found to be the only visitor to the small, zygomorphic flowers (8—10 mm long) of Melasphaerula ramosa, a species endemic to the southern African winter-rainfall zone. Each captured fly carried the pollen of M. ramosa exclusively, with grains deposited on the dorsal part of the thorax. Observations showed that these insects contacted both dehisced anthers and stigmatic surfaces of style branches while evidently foraging on nectar secreted from septal nectaries into the base of the floral tube. Experimental hand pollinations showed that M. ramosa is self-compatible, and some flowers undergo mechanical self-pollination (autogamy) in the absence of insect visitors. Pollination of this genus of Iridaceae by bibionids represents a new syndrome within the broad category of fly pollination and expands the range of pollination mechanisms reported in this family. As there is comparatively little scientific literature confirming bibionid pollination throughout the world, we compare the floral biology of M. ramosa with available litrerature on pollination by other microdipterans in the Araceae, Hydrophyllaceae, Saxifragaceae, Orchidaceae, and Sterculiaceae.