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

Fruit and seed production in a natural population of a dioecious plant: Piliostigma reticulatum HOSCHT (Caesalpinioïdeae)

Plant fruit/seed production is a central subject of many questions in plant evolutionary and conservation biology. In the Sudano-Sahelian forest of Burkina Faso, fruit and seed production of a common dioecious shrub, Piliostigma reticulatum, were assessed by considering plant size, fruiting success and distance between male and female individuals. The results showed that P. reticulatum has a low production of fruits and seeds (17.63 g ± 3.33 SE of fruit per plant and 0.1045 g ± 0.0018 SE per seed). A large percentage of the seeds aborted (40%) and were damaged by herbivory (10%). The fruiting success ranged from 0.1 to 0.4. The percentage of seeds attacked by insects was negatively correlated with the mean diameter of the canopy and the height of trees. When the female of P. reticulatum was more than 10 meters from the male, fruit and seed productions were greater. The conclusion was that losses of flowers and fruits were important and suggested further information on pollination limitation or genetic studies to identify the cause of the insufficient quality and quantity of fruit and seed productions of P. reticulatum.Keywords: Piliostigma reticulatum, dioecious, fruiting success, soudanian forest, Burkina Fas