Pollination by megachilid bees and determinants of fruit‐set in the Cape orchid Disa tenuifolia

Wild‐fires near Cape Town, South Africa, stimulated mass‐flowering in several populations of Disa tenuifolia (Orchidaceae). We found that the bright yellow flowers of the orchid are pollinated by various carder and leafcutter bees (Megachilidae) and occasionally monkey beetles (Scarabaeidae: Hopliini). The highly elongate pollinaria become attached to the underside of the pollinator's thorax. The bees showed strong fidelity towards the orchid, despite the lack of nectar in its flowers. The orchid does not appear to mimic other rewarding species. It was concluded that the pollination system of D. tenuifolia depends on exploitation of instinctive foraging and territorial behaviour of male megachilid bees. The fruiting success of D. tenuifolia at the study site was pollinator‐limited as supplementary hand‐pollinations resulted in a two‐fold increase in the percentage of flowers which set fruit.