BRANSTETTER, M. G.; The Evergreen State College: Oil-collecting structures of the South African bee genus Rediviva (Hymenoptera, Mellitidae): An investigation using scanning electron microscopy

Bees have been coevolving with flowering plants for millions of years and have as a result a wide range of adaptations for collecting many different types of floral rewards. In addition to being adapted to collecting nectar and pollen, many bees have specially modified structures for the extraction of floral lipids, which are produced by special secretory glands called elaiophores. Rediviva (Hymenoptera, Mellitidae) is an oil-collecting genus of bees occurring in southern Africa. It has undergone diffuse coevolution with oil-producing flowers in the family Scrophulariaceae, primarily with species in the genus Diascia, and some Orchidaceae. Modifications in both plant and pollinator are evident: many Diascia species have long elaiophore containing spurs and many female Rediviva species have disproportionately long forelegs with specially adapted oil-collecting setae. Using scanning electron microscopy, I have been able to document the diversity in oil-collecting structures of 23 Rediviva species and compare it with Rediviva males and several non oil-collecting species in closely related genera. As hypothesized, only the oil-collecting Rediviva bees have specialized setae, which can be found on the foretarsus of all species and both the fore- and midtarsus of several. Setae type range from being thin and highly branched, forming dense tomenta, to being broad and spatulate. Like several investigations into the oil-collecting structures of Neotropical and Holarctic bees, this new research combined with other data about Rediviva species systematics, distributions, and host plants should bring new understanding to this unique mutualistic plant-pollinator relationship.