EFFECT OF INSECT POLLINATION ON FRUIT SET AND YIELD OF SHEA (Vitellaria paradoxa) IN THE GUINEA SAVANNAH ZONE OF GHANA

Abstract

Shea (Vitellaria paradoxa) is an important economic tree in West Africa with multipurpose uses. It is the most abundant economic tree species in the three regions of northern Ghana. Understanding the contribution of insect pollination to fruit production is fundamental to effective management and conservation, yet such information on Vitellaria paradoxa is rare in Ghana. The study was carried out from January to August, 2016 to determine the effect of insect pollination on the reproductive success of Vitellaria paradoxa in cultivated parklands. The study also estimated the monetary value of the contribution of insect pollination to the yield of Vitellaria paradoxa. Open pollination and insect exclusion treatments were applied to the flowers of 18 randomly selected matured shea trees. Insect visitors of the flowers were identified and insect to flower visitation rates were also monitored. Six insect species comprising of three species from the stingless bees and one species from the honeybees were identified as insect pollinators of Vitellaria paradoxa out of the 187 insect visitors collected from the flowers. The experiment shows 73% of Vitellaria paradoxa yield is dependent on insect pollination. Flowers that had access to insect pollination produced a significantly higher mean number of matured fruits per inflorescence as compared to insect excluded flowers. Insect to flower visitation rate had a positive relationship with the number of matured fruits produced. The monetary value of the contribution of insect pollinators to yield was GH₵ 73.21 per bag of kernel (per market price in August, 2016). The study revealed that declines in insect pollination services can significantly affect fruit production. It is therefore recommended that farmers should incorporate pollinator-friendly practices into landuse to help conserve pollinators in shea parklands.