Unexpected Contribution of the Introduced Honeybee Apis mellifera to High Fruit Set in Spiranthes australis (Orchidaceae)

ABSTRACT: We studied the pollination biology of a native orchid Spiranthes australis in Kobe, Hyogo, Japan, and observed that S. australis flowers are frequently visited by the managed honeybee A. mellifera. Since the honeybees extracted pollinaria from the anthers and deposited pollinia on the stigmas of many flowers, the behavior resulted in the successful pollination of multiple flowers even in a single visitation. Given that (i) the honeybee was the most frequent and intensive pollinator during our observation period and (ii) the fruit set in the investigated population was significantly higher than the fruit set of a previously investigated S. australis population, despite lack of ability for autonomous self-pollination, A. mellifera may promote a high reproductive success in S. australis. Our observation provides some insight into the diversity of orchid-pollinator interactions, drawing attention to the potential importance of non-native bees as pollinators.