POLLINATION BIOLOGY OF HYDNORA AFRICANA THUNB. (HYDNORACEAE) IN NAMIBIA: BROOD-SITE MIMICRY WITH INSECT IMPRISONMENT

Hydnora africana is a root holoparasite of southern Africa that emerges only to flower. The trimerous flowers of H. africana have androecial and gynoecial chambers and attract floral visitors with putrid odors emitted from prominent osmophores. We observed floral phenology and insect visitation for H. africana at two sites in southern Namibia and evaluated the insect imprisonment mechanism with beetle addition and pollen viability assays. Flowers are putatively protogynous for 3 d. We observed 18 floral visitors, including 10 coleopteran species imprisoned by the smooth inner surface of the androecial chamber. The hide beetle Dermestes maculatus (Tenebrionidae) accounted for 76.9% of the imprisoned insects, with a density of 2.2 +/- 0.6 per flower. The D. maculatus addition experiment (n = 9) clearly demonstrated imprisonment during the carpellate stage. Changes in the inner surfaces of the androecial chamber, stippling, and texturing allowed D. maculatus to escape after pollen release. More than 55.5% of the beetles escaped, dusted with pollen, within 3 d after pollen release. Pollen was still viable 3 d after pollen release. The beetle addition and pollen assays demonstrate the efficiency of the H. africana imprisonment mechanism.