Diversity and efficiency of wild pollinators of watermelon (Citrullus lanatus (Thunb.) Mansf.) at Yatta (Kenya)

Abstract: Citrullus lanatus (Thunb.) Mansf. (Watermelon) is an important crop plant in Kenya. Being monoecious, watermelon is entirely dependent upon pollination services usually by insects for production. Although the centre of origin for this plant is thought to be tropical Africa, essentially not much has been studied of its pollination requirements in this region. The current study investigated the identity of the wild pollinators of watermelon, their behaviour and relative pollination efficiencies at Yatta, a farm near Thika (Eastern Province). The main pollinator for this crop was found to be the honey bee, Apis mellifera but three wild species of Lasioglossum were found as important pollinators. These wild bees have a significantly higher (P< 0.0001) pollen deposition on stigmas of watermelon than honeybees. One of the Lasioglossum (Ctenonomia) sp. 4 deposited on average three times as much pollen as the honeybee. At about the time of stigmatic receptivity, the number of visits by this species to female flowers increases until it equals visits to male flowers irrespective of number of flowers per plot. This behavioural pattern coupled with the high pollen deposition potential makes Lasioglossum (Ctenonomia) sp. 4 a superior candidate as an alternatively managed pollinator for watermelon. Knowing that visitation occurs mostly in the morning, and that flowers last only for one day, spraying can be done in the later hours of the day when the pollinators have virtually stopped foraging on the flowers. In view of the reported pollinator decline globally, the wild pollinator species reported in this study warrant further investigation on their nesting biology and potential for domestication.