Floral Visitors and Fruit Set in Afgekia sericea Craib (Fabaceae)

Abstract

Afgekia sericea Craib (Fabaceae) is an endemic leguminous plant of Thailand. It is becoming rare due to fragmentation of its natural habitats which is probably leading to a reduction of reproductive success. This study investigated the interaction of the plant and its floral visitors in relation to fruit and seed set in three study sites which had different degrees of habitat disturbance. Sixteen bees, one small butterfly, one beetle and one sunbird were found to be visitors, but we found that only eleven bee species in the three genera, i.e. Megachile, Nomia, and Pithitis take part in the pollination. Some of these bees were particularly effective pollinators, especially M. velutina was found to be legitimate pollinator for A. sericea. The abundance of effective pollinating insects decreased markedly as the degree of habitat disturbance increased. These insect visitors are attracted by nectar guides on the vexillum and rewarded by pollen and/or nectar. Experiments in which flowers were enclosed in bags, thus preventing access by insects yielded no fruit set, while open pollination that allowed insects to visit flowers, resulted in fruit setting. These results indicate clearly that fruit set in this legume species depended largely on bee pollinators. However, percentage of fruit set was extremely low since less than 0.2% was observed from two natural sites.