Abundance and Diversity of Bee Pollinators in Common Bean (Phaseolus Vulgaris L.) Agroecosystems along A Forest-Agriculture Gradient in Borabu, Kenya

Abstract

Declining bee colonies have led to reductions in food production worldwide. Nevertheless, little is known about crop pollination in African countries, especially in Kenya, where pollination studies lack harmonization and only a few crops have been studied. This study sought to determine the abundance and diversity of bee pollinators visiting common bean (Phaseolus vulgaris) flowers along a forest agriculture gradient, evaluate the effect of caged and uncaged pollination treatments on pod and seed set of common beans, and assess the level of farmers' indigenous knowledge of bee pollinators of common beans in Borabu Sub-County, Kenya. Nyansiongo Administrative Sub-location was purposively selected. A survey was conducted along three plots, extending from the forest edge of the natural habitat into the surrounding farmlands. Sampling points were established at 0.3 km intervals along each plot. Pollinator sampling was undertaken within 100 m² bean plots located at the designated sampling points. Sampling was conducted three times a week between 0730 hrs and 1200 hrs during the flowering period. Bee sampling was carried out for three months from January to March 2018 using sweep nets and pan traps. The pan traps consisted of three conspicuous colours; blue, white, and yellow which were randomly positioned at ground level within each 100 m² bean plot. Questionnaires were administered to bean farmers and bean farm managers to obtain information on bean crop pollination. Beans from each treatment were weighed, recorded, and their data analysed using a t-test. Diversity was computed using Shannon's diversity index, while abundance was determined using abundance curves. A total of 992 bee visitors belonging to two families and eight species were collected from the three study farms. The bee species diversity index (H′) yielded a value of H′ = 0.55. There was an increase in crop quality and yields due to bee pollination. There was no significant difference between the number of pods in closed and open bean flowers (p > 0.05). There was a significant difference in seed weight between caged and uncaged bean plants (p < 0.05). There was also a significant difference in seed number between caged and uncaged bean plants (p < 0.05), as well as seed weight (p < 0.05). This confirms that bees enhance bean yields by improving both quality and quantity. Apis mellifera was the most commonly recognized bee species, as indicated by 42.7% of male respondents and 75.0% of female respondents, followed by Xylocopa calens, identified by 28.6% of male and 18.8% of female respondents, while Meliponula sp. and Megachilidae sp. were identified only by 7.1% of male respondents. There was no significant difference (p > 0.05) between male and female respondents regarding the methods or inputs used to enhance pollination. This indicates that awareness on pollination issues should target both male and female farmers. Therefore, farmers and other stakeholders should be sensitized and trained on the importance of bee pollination, its contribution to their welfare, and the utilisation of cost-effective strategies for bee conservation.