Introducing managed honey bee hives into natural fynbos of South Africa: effects on pollinators and their dependant plants

Abstract

Honey bees (Apis mellifera) are economically important managed pollinators for the agricultural industry. Their use is widespread across the world, however, they are only native to Africa and parts of Europe and Asia. In the Cape Floristic Region (CFR) of South Africa, an indigenous honey bee subspecies, Apis mellifera capensis (Cape honey bee) is used for agricultural pollination services. Agricultural crops are used as forage for bees in spring, eucalyptus trees in summer, and natural vegetation is required throughout the winter months. However, honey bees’ presence in natural areas in high densities could lead to negative impacts on unmanaged pollinators and their dependent plants, but scientific evidence in support of these actions is largely lacking in the South African context. My objectives in this thesis were to determine the effect of introducing managed honey bee hives (MHBH) on pollination networks, flower visitation rates, community composition of pollinators, insect diversity and abundance, and plant reproduction. To examine these effects, two different study sites were sampled under different conditions. Chapter two investigates these effects with the controlled introduction of 10 MHBH during winter while in chapter three these effects are investigated through the uncontrolled dumping of up to 400 MHBH during summer. There were no other known MHBH within a 3 km radius of the MHBH introduced in this study. For both chapters, data were collected through pollinator flower visit observations and pan traps from four plots within 1 km of MHBH. For chapter two, data was collected for 10 days with no MHBH present (before hives) and then for 10 days after MHBH were introduced (during hives). In both chapters, increased honey bee hive density increased honey bees flower visitation rate while density of dipteran species decreased, pollination networks were dominated by honey bees and community composition became significantly more homogenous. Abundance of Hymenoptera and flower visitation rates did not decrease due to MHBH introductions. Coleoptera abundance increased significantly in plots where honey bees did not increase significantly. Floral composition and distribution in the landscape affected how honey bees were distributed, with bees showing a preference for generalist Asteraceae flowers. Seed set of Cullumia reticulata (Asteraceae) was not affected by the introduction of MHBH. In both instances of the study, where in one case the MHBH introductions were controlled and the other not controlled, some insect groups were affected more than others. Hymenoptera were seemingly unaffected, Diptera was affected and Coleoptera showed some avoidance of areas of high honey bee abundance. Ultimately, the availability of floral resource (type and abundance) will affect how honey bees congregate in the landscape. Even though these findings do have some limitations, they will contribute towards conservation and management plans for protected areas, where such data is currently lacking, to guide the decision-making process.