Assessing the potentials of agricultural ecosystem pollination services to improve bean yield in smallholder farming systems

A Thesis Submitted in Partial Fulfilment of the Requirements for the Degree of Doctor of Philosophy in Life Sciences of the Nelson Mandela African Institution of Science and TechnologyPollination services by insects contribute to production in 75% of food crop species. When promoted through agro-ecological intensification (AEI), pollination can narrow yield gaps in smallholder farming systems. The study evaluated the contribution of insect pollinators on common beans (Phaseolus vulgaris L.) yields, and the knowledge gaps pre and post-training of smallholder farmers (n=300) in pollinators and field margins in a bean agro-system were investigated. Also, the role of field margin as a refuge for flower-visitors, and how plants and pollinator richness and diversity can influence strength of pollination networks in three agro ecological zones were investigated. Baseline and end-line surveys, pollinator exclusion and fluorescent dye-experiments, insects and vegetation surveys were carried out to obtain data for each specific objective of the study. While the majority of farmers were unaware of pollinators and their importance as pollinators before training, the end-line survey one year after training showed an increase in knowledge. The majority of farmers subsequently recognized honeybees, hoverflies and solitary bees, by names and their role as crop pollinators and natural enemies (for the case of hoverflies). Higher yield based on pods per plant and seeds per pod on open pollinated and hand pollinated flowers were significantly recorded compared with plants from which pollinators had been excluded suggesting that pollinators contribute significantly to crop yield. Similarly, it was found that field margin plants are essential in supporting higher number of pollinator taxa and can influence their richness in adjacent bean field. Collectively these results showed that improving understanding among smallholder farmers of ecosystem services and their ecological requirements are both feasible and essential for conservation of insect pollinators, which are important for optimising yield in this production system, and that crop margin vegetation provides habitat for these ecosystem service providers. Field margins with high plant diversity displayed extended and more robust pollination networks compared to those with low plant diversity, and consequently these habitat strips should be managed with sensitivity for pollinating insects and for the stability and persistence of plant-pollinator interactions in this agro-system

Enhancing knowledge among smallholders on pollinators and supporting field margins for sustainable food security

Agro-ecological intensification (AEI) harnesses natural processes, such as pollination, that support sustainable food production and can buffer against future risks. However, the transition from conventional agriculture, which relies on inputs that can damage natural ecosystems, to more sustainable food production, is knowledge-intensive. Here, we investigated knowledge gaps among smallholder farmers about pollinators and field margins in a bean agri-system in Tanzania. While 77% of farmers were familiar with and identified honeybees correctly prior to training, only 52% understood their role as a pollinator of crops. Furthermore, 80% and 98% of farmers were unaware of the significance of wild (solitary) bees or the importance of hoverflies as pollinators. A high level of synthetic agrochemical use was reported for the management of pests and weeds, particularly in the more agriculturally intensive production systems. However, an end-line survey conducted one year after training showed an increase in knowledge and the majority of farmers, 99%, 54% and 62% subsequently recognized honeybees, hoverflies and solitary bees respectively, by name. Furthermore, 95%, 69% and 60% of farmers understood the importance of honeybees, hoverflies and solitary bees respectively, as crop pollinators and natural enemies (for hoverflies). Similarly, a majority of farmers recognised the benefits of biopesticides as environmentally over synthetic pesticides as well as the value of field margins in supporting pollinators and other ecosystem services. We argue that, improving understanding among smallholder farmers of ecosystem services and their ecological requirements is both feasible and essential to achieving sustainable intensification in small holder farming systems

Insect pollination is important in a smallholder bean farming system

Background: Many crops are dependent on pollination by insects. Habitat management in agricultural landscapes can support pollinator services and even augment crop production. Common bean (Phaseolus vulgaris L.) is an important legume for the livelihoods of smallholder farmers in many low-income countries, particularly so in East Africa. While this crop is autogamous, it is frequently visited by pollinating insects that could improve yields. However, the value of pollination services to common beans (Kariasii) yield is not known. Methods: We carried out pollinator-exclusion experiments to determine the contribution of insect pollinators to bean yields. We also carried out a fluorescent-dye experiment to evaluate the role of field margins as refuge for flower-visitors. Results: Significantly higher yields, based on pods per plant and seeds per pod, were recorded from open-pollinated and hand-pollinated flowers compared to plants from which pollinators had been excluded indicating that flower visitors contribute significantly to bean yields. Similarly, open and hand-pollinated plants recorded the highest mean seed weight. Extrapolation of yield data to field scale indicated a potential increase per hectare from 681 kg in self-pollinated beans to 1478 kg in open-pollinated beans indicating that flower visitors contributed significantly to crop yield of beans. Our marking study indicated that flower-visiting insects including bees, flies and lepidopterans moved from the field margin flowers into the bean crop. Overall, these results show that insect pollinators are important for optimising bean yields and an important food security consideration on smallholder farms. Field margin vegetation also provides habitat for flower-visiting insects that pollinate beans. Hence, non-crop habitats merit further research focusing on establishing which field margin species are most important and their capacity to support other ecosystem services such as natural pest regulation

Beneficial insects are associated with botanically rich margins with trees on small farms

Beneficial insect communities on farms are influenced by site- and landscape-level factors, with pollinator and natural enemy populations often associated with semi-natural habitat remnants. They provide ecosystem services essential for all agroecosystems. For smallholders, natural pest regulation may be the only affordable and available option to manage pests. We evaluated the beneficial insect community on smallholder bean farms (Phaseolus vulgaris L.) and its relationship with the plant communities in field margins, including margin trees that are not associated with forest fragments. Using traps, botanical surveys and transect walks, we analysed the relationship between the floral diversity/composition of naturally regenerating field margins, and the beneficial insect abundance/diversity on smallholder farms, and the relationship with crop yield. More flower visits by potential pollinators and increased natural enemy abundance measures in fields with higher plant, and particularly tree, species richness, and these fields also saw improved crop yields. Many of the flower visitors to beans and potential natural enemy guilds also made use of non-crop plants, including pesticidal and medicinal plant species. Selective encouragement of plants delivering multiple benefits to farms can contribute to an ecological intensification approach. However, caution must be employed, as many plants in these systems are introduced species