Insect pollinator dependence of shea (Vitellaria paradoxa C.F. Gaertn.) in the Guinea Savanna zone of Ghana

Abstract

Shea (Vitellaria paradoxa C.F. Gaertn.) is a multipurpose tree species indigenous to the Sudano Sahelian zone of Africa and occurs as the most abundant economic tree species in northern Ghana. The edible oil (shea butter) extracted from shea kernel is ranked as the most economic product of the species. Although fruit set and yield of shea are known to be influenced by insect pollination, the actual contribution of insect pollinators to its reproductive success has rarely been studied. This study estimated the percentage insect pollinator dependence and monetary value of insect pollination per bag of shea kernel (85 kg) in the Guinea savanna zone. Open pollination and insect exclusion treatments were applied to the flowers of 18 randomly selected matured shea trees and observed from the onset of flowering to fruit maturity. Proportion of total production value attributed to insect pollination approach was used in estimating the monetary value of pollination per bag of shea kernel with the average market price as proxy. The study revealed an insect pollinator dependence of 77% and 73% for fruit set and dry kernel yield, respectively. Mean number of fruit set per inflorescence varied significantly between insect-excluded and open-pollinated inflorescences (p < 0.05). The monetary value of insect pollination was estimated at GH₵ 73.21 (US$ 18.67) per bag of kernel as of August 2016. Shea is a high insect pollinator–dependent species and the conservation of insect pollinators would be critical to the sustainability of yield.