Bee size and pollen transfer in Cypripedium calceolus (Orchidaceae)

In Denmark Cypripedium calceolus is found in only two small and isolated populations, and its fruit set is suspected to be pollinator-limited. Collection and observations of flower visitors were carried out between 1995 and 1997, and fruit set were estimated. Forty-four visitors were collected. The majority belonged to the genera Halictus, Lasioglossum and Andrena . The latter is known as pollinator of C. calceolus in other parts of Europe, but in this study Andrena spp. were both not regular visitors and too large to function as efficient pollinators. Medium-sized halictine species, especially females of Halictus tumulorum and Lasioglossum calceatum , were the most regular and frequent pollen vectors. Andrena jacobi and Lasioglossum rufitarse are recorded for the first time in Denmark.