Pollination and facultative ant-association in the African leopard orchid Ansellia africana

Abstract

The leopard orchid Ansellia africana (Orchidaceae) is an epiphytic species widely distributed across tropical Africa. The pollination ecology of A. africana was investigated by direct observation. Buds and stalks of A. africana exude droplets of extra-floral nectar, but mature flowers produce no nectar. The role of extra-floral nectar appears to be recruitment of foraging ants to tend the flowers resulting in a facultative ant-association between the orchid and gregarious ants. Four different ant species were found to forage on A. africana’s inflorescences. Ant-tended inflorescences suffered significantly less damage by insects. Mature A. africana flowers are non-rewarding which suggests a deceit pollination mechanism being employed by this orchid. The pollinators of A. africana were observed to be wild solitary bees species in the genera Xylocopa, Amegilla (Apidae) and Gronocera (Megachilidae).  Observations of bee visitors to A. africana revealed overall lowvisitation rates but adequate fruit set despite the non-rewarding flowers. Solitary bees visiting A. africana were ‘deceived’ by the flowers, but attracted to the floral displays and scent. A. africana shows spatial and temporal manipulation of two distinct suites of insects, ants and solitary bees.