Pollinator diversity, behaviour and limitation on yield of karela (Momordica charantia L. Cucurbitaceae) in Western Kenya

Abstract

Inadequate pollination is a major constraint to crop yield. Momordica charantia L. is a fruit crop of economic interest in Kenya. Pollination ecology, pollinator diversity and their behaviour were studied in Western Kenya. Pollination treatments included insect exclusion, open pollination (unrestricted insect visits), hand cross-pollination and pollen augmentation. Yield components from treatments were compared to identify the pollination requirements of this crop. Flowering started 45 days after germination with the staminate flowers appearing first followed by rewardless pistillate flowers. The ratio of pistillate to staminate flowers was 1: 13. Pollinator species included honey bees (Apis mellifera), Plebeina hildebrandti, Lasioglossum sp. and carpenter bees (Xylocopa spp). Fruit set and yield were pollen limited as all bagged flowers were aborted. Fruit set under natural pollination was very low and this revealed the degree of pollen limitation in M. charantia. Low fruit set was consistent with observation of high discrimination against pistillate flowers amongst potential pollinators. Smaller bees belonging to families Apidae (Plebeina hildebrandti) and Halictidae (Lasioglossum sp.) were the most important pollinators. These observations highlight the importance of (1) a diverse fauna of wild bees and (2) the potential of meliponiculutre in the increasing the yield of M. charantia in Kenya. Key words: Plebeina hildebrandti, Lasioglossum, discrimination, deceit pollination, yield.