Suitability of Hedgerow Planting System in Managing Bee (Hymenoptera: Apoidae) Pollinators in Farmlands of Kenya
Guantai, Mary Mwari
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Bee presence in the farmland is crucial for provision of essential crop pollination service. However, this is highly determined by the availability of forage resources and nesting sites among others. Therefore, the overall aim of this study was to determine suitability of hedgerows in providing bee needs in Kenya. Specifically, the study was carried out to determine i) bee nest presence in farmlands bordering Mt. Kenya, Mt. Kilimambogo and Kakamega forests, ii) the floral richness of hedgerow plants in farmland bordering NW Mt. Kenya forest, and iii) diversity and abundance of bees visiting hedgerows in farmlands bordering NW Mt. Kenya forest. The data were collected through i) excavation and characterization of solitary bee nests along a transect from fields near the forest to fields 15 km away, ii) observation of floral resources for period of 1 year (September 2013 to August 2014) along a transect from fields near the forest to fields 15 km away and ii) observation of bees visiting flowers of hedgerow plants for period of 1 year along a transect from fields near the forest to fields 15 km away. Their presence on hedgerow plants was compared with those present on cropped area and uncropped patches in the field. The number of bee nests was statistically (P<O.OOI)higher in fields far from the forest implying that forests provide essential nesting sites for farms close to the forest. Kakamega and Kilimambogo farmlands had higher number of bee species recorded showing that farm practices are friendlier to bees in those sites. Hedgerow plants hosted most of the bee nests indicating that if properly managed they can be used to manage bee presence in the farmland. Nests for large bees e.g., Xylocopa spp. were located on the house rafters, indicating that hedgerow plants could not offer better sites for these bees unless concerted efforts are put in place to include large bee nest sites. There was high diversity and density of flowers across the year in the hedgerow plants indicating that bee forage needs can be sustained in the farmland. The most important bee forage plants were Aspilia mossambicensis and Plectranthus barbatus, which were recorded in all the farmlands. Sixteen bee species belonging to three families (Apidae, Halictidae and Megachilidae) were recorded. The species richness curve showed a possible presence of more species in the farmland. This indicates that proper management of bee food and nests can increase their density. Honey bees (Apis mellifera) were the most abundant as expected a priori due to their sheer number and domestication. However, with proper bee management, the density of other bees such as carpenter bees can be enhanced. It is suggested that an integrated hedgerow management that includes keeping plants with yellow, purple, white and pink flowers and inflorescence (particularly those belong to family Asteraceae and Lamiaceae) as well as including dead wood for large bees be implemented to enhance solitary bee presence in the farmland. This should be implemented in an area-wide approach to provide connectivity within the farmland and natural habitats for food resources, nesting sites and refugia of bees.