New records of insect pollinators for South African asclepiads (Apocynaceae: Asclepiadoideae)

Studies of pollination in southern African asclepiads (aside from the stapeliads and members of the genus Ceropegia) are remarkably scarce given the diversity of asclepiad species in the region. In this study, we report new observations of insect flower visitors and their pollen loads for 15 species of South African asclepiads in the genera Asclepias, Aspidoglossum, Miraglossum, Pachycarpus, Periglossum, Woodia and Xysmalobium. Nectar properties are also presented for some species. Four specialized pollination systems are suggested by these observations: (1) pollination by wasps in the genus Hemipepsis (Hymenoptera: Pompilidae) in eight species, (2) pollination by chafer beetles (Scarabaeidae: Cetoniinae) in three species, (3) pollination by honeybees, Apis mellifera (Hymenoptera: Apidae) in two species, and (4) pollination by flies from various families in one species. The pollination system of Asclepias crispa remains unclear but appears to be one of generalized insect pollination. Future research is likely to confirm the preponderance of specialized pollination systems within this group of plants in southern Africa.