How do rewardless Bletilla striata flowers attract pollinators to achieve pollination?

Abstract

Rewardless plants use various strategies to attract pollinators. Generalized food-deceptive species exploit the nonspecific food-seeking responses of their pollinators. Because past experiences are important for establishing the food-seeking behaviors of insects, previous flower visits by pollinators should play crucial roles in rewardless plants. In this study, we investigated previous experiences of insects that visited the rewardless orchid Bletilla striata based on pollen attached to their bodies to clarify whether experience of visiting flowers with similar colors as rewardless flowers is necessary. Contrary to the expectation, less than half of the flower visitors carried pollen of flowers with similar colors as B. striata, implying that past experience is not essential. Furthermore, we investigated the effects of learning based on the association between the flower position and fruit set assuming that the fruit set would decrease with the progression of the flowering season. A significant association was found at only one of the three study sites. Among flower visitors, male long-horned bees (Eucera spurcatipes) and honeybees (Apis mellifera) primarily carried B. striata pollinia. We hypothesize that B. striata uses generalized food deception to attract honeybees and rendezvous attraction to attract mate-searching male long-horned bees and that this mixed strategy invalidates the associations assumed in generalized food deception.