Consistent pollination services to Cypripedium macranthos var. rebunense (Orchidaceae) by Bombus pseudobaicalensis

Abstract

Bombus pseudobaicalensis queens are known pollinators of the threatened orchid Cypripedium macranthos var. rebunense. However, whether other bumblebee species also pollinate this orchid has not yet been ascertained. A 10-year observation provided convincing evidence that B. pseudobaicalensis is the only consistent pollinator. B. beaticola moshkarareppus queens were newly found to rarely carry pollen smears of the orchid, whereas B. hypocrita sapporoensis and B. diversus queens were practically mere flower visitors. Why these three species do not equal B. pseudobaicalensis in pollination effectiveness remains unclear but differences in body size and individual abundance between B. pseudobaicalensis and the other species are considered as possible primary causes. Given the almost complete dependence of C. macranthos var. rebunense on B. pseudobaicalensis for pollination and its potential risk, conservation managers should take care not to reduce the bumblebee colonies.