Wekhanya, Marystella Nang’oni2025-09-012025-09-012025-06https://ir-library.ku.ac.ke/handle/123456789/31322A thesis submitted in fulfilment of the requirements for the award of the degree of doctor of philosophy in plant ecology in the School of Pure and Applied Sciences of Kenyatta University, June 2025 Supervisors: Prof. Rebecca Karanja Dr. Muo Kasina Dr. Mary Mwari GuantaiPollinator reservoirs can augment pollination of flowering crops and increase agricultural crop production. Despite this recognized importance, there is a critical knowledge gap concerning the biodiversity of pollinator forage resources within croplands and their utilization by honeybee (Apis mellifera). Pumpkin (Cucurbita maxima L.), a member of the Cucurbitaceae family, is an economically important food crop globally contributing to household food security. As a pollinator-dependant crop, its production remains low, a constraint largely attributed to an insufficient supply of pollinators. Therefore, the main objective of the study was to determine the annual floral resource structure and its utilization by honeybee pollinators within pumpkin growing farms in Yatta and Masinga sub-counties, Machakos county. To achieve this, four specific objectives were established: to determine the abundance and diversity of flowering plants present in pumpkin farms; to determine the phenology of the non-pumpkin flowering plants utilized by honeybees; to determine the diversity of pollen sources deposited within beehives; and to determine if there is pollination inhibition in pumpkin flowers due to foreign pollen. The study was conducted starting in November 2019 to August 2020. Data was collected on 32 pumpkin-growing farms that were differentiated using Normalized Difference Vegetation Inddex whereby (16 farms were in low NDVI and 16 farms in medium); NDVI is a measure of vegetation greenness and density. Flowering plants abundance and diversity data were collected in the middle of the farm using one quadrat 2 m x 2 m and a belt transect 4 m x 50 m was used to collect data from the middle of the pumpkin farm towards the exit of the farm (non-crop area). Data within the belt transect was collected at intervals of after every one meter. Data were analyzed using the Shannon-Weiner Index. The phenology of non-pumpkin plants utilized by honeybees was determined using monthly plant data that was used to develop a floral calendar. Identification and classification of plants and pollen pellets collected from the beehives was carried out at the National Museum of Kenya. Results revealed thirty five percent of the plants within the sampled areas remained actively flowering throughout the sampling period, serving as alternative forage sources for pollinators. The abundance of plant species varied between NDVI classes and across months; one hundred and forty-two plant species were recorded. A significantly higher abundance of plant species was recorded in low NDVI farms; 6,765 plants compared to 4,399 plants recorded in May. Pollen analysis revealed one hudred and fifteen pollen species from different plant families and the families frequently visited by honeybees were Asteraceae, Solanaceae and Typhaceae. Areas with higher vegetation density and diversity indicated by medium NDVI support a rich array of flowering plants. This translated to greater pollinator forage diversity, as evidenced by the finding that A. mellifera foraged from sixty-one plant genera in low NDVI farms, whereas they utilized one hudred and three plant genera in medium NDVI farms. In both NDVI, the predominant pollen (more than fourty five percent) sources were from Chenopodium spp in low NDVI and Vernonia spp in medium NDVI. Analysis of pollen deposited on pumpkin stigmas revealed that the number of pollens deposited on the stigma differed significantly among the major group of plants (χ2 = 8938.30, df = 9, p < 0.0001). This means that despite honeybees foraging on diverse non-pumpkin plants, pollen deposited on stigmas originated from pumpkin. In conclusion, the study shows that there is abundance and diversity of non-crop flowering plants within and around the pumpkin farms that act as reservoirs for pollinators. Information on the phenology of key pollinator forage plants will serve as a vital tool for on-farm management of pollinators by farmers. This will ensure a continuous supply of pollinators and consequently enhance pumpkin yields.enThesis