Bombus pseudobaicalensisqueens are known pollinators of the threatened orchidCypripedium macranthosvar.rebunense.However, whether other bumblebee spe-cies also pollinate this orchid has not yet been ascertained. A 10-year observationprovided convincing evidence thatB. pseudobaicalensisis the only consistent pol-linator.B. beaticola moshkarareppusqueens were newly found to rarely carry pol-len smears of the orchid, whereasB. hypocrita sapporoensisandB. diversusqueens were practically mere flower visitors. Why these three species do not equalB. pseudobaicalensisin pollination effectiveness remains unclear but differences inbody size and individual abundance betweenB. pseudobaicalensisand the otherspecies are considered as possible primary causes. Given the almost completedependence ofC. macranthosvar.rebunenseonB. pseudobaicalensisfor pollina-tion and its potential risk, conservation managers should take care not to reduce thebumblebee colonies.
