Flowering phenology and floral visitors of Piliostigma reticulatum in a tropical dry forest, Burkina Faso

Piliostigma reticulatum is a dioecious species that provides food, fodder and the revenues from the sale of its pods constituted an important resource for sahelian population. During the flowering, flowers are abundant but the fruit set remained very low in spite of a large number of insect visitors. The aim of this work was to study flowering phenology, to identify potential pollinators and visitors, to determine the visitation rate and the synchronism between floral phenology and the insect visitors. The natural population studied is located at Budtenga in the North Sudanian area of Burkina Faso. The phenological study was carried out from July 2009 to December 2009 on 500 inflorescences randomly sampled from inflorescences of 40 male and female individuals. Potentials pollinators were determined using their physical ability to carry pollen in their body and the reference based diets. Our results showed that many orders of insects visit the flowers of P. reticulatum. Nymphalidae (Lepidoptera), Syrphidae (Diptera), Apidae (Hymenoptera) and Sphecidae (Hymenoptera) were regarded as main potential pollinators of P. reticulatum. Apidae (Apis mellifera) was the most abundant and frequent visitor. We found that August was the peak flowering period for both male and female individuals and the peak emergence of potential pollinators. Therefore, the emergence of potential pollinators responsible for pollen dispersal might be punctuated by flowering phenology.Keywords: Caesalpinioideae, P. reticulatum, phenology, visitors, Sudanian fores