Improving the health and survivorship of commercial honey bee colonies

Abstract

The health of honey bees (Apis mellifera L.) is essential for the health of U.S. agricultural and natural ecosystems. In particular, the sustainability of commercial beekeeper operations (beekeepers that manage >500 colonies) is of critical importance to agriculture as these operations manage most of colonies in the U.S. and fulfill the majority of crop pollination contracts. Identifying risk factors and best management practices for these beekeepers can improve colony health and survivorship, decreasing total U.S. colony mortality. My dissertation uses epidemiological methods to identify and quantify risk factors in real-world commercial beekeeping operations in four chapters. Chapter 1 reviews recent publications that use epidemiological methods to study honey bee health. The reviewed research efforts used surveillance methods to quantify colony mortality, describe disease prevalence and incidence, and identify risk factors. Surveillance can be used to highlight potential areas of further research and measure improvements in honey bee health. Chapter 2 quantifies the problem of colony mortality by reporting the results of the eighth year (2013 – 2014) of the Bee Informed Partnership’s annual colony loss survey. The survey reports on summer, winter, and annual colony mortality of 7,425 voluntary respondents representing approximately 19% of U.S. colonies, and includes different beekeeper operation sizes, regions, and migratory statuses. Although only 1.4% of respondents were commercial beekeepers, they managed 89% of the colonies represented in this survey. Similar to previous surveys, commercial beekeepers had lower winter and annual loss than beekeepers that managed fewer colonies, with summer losses not different among beekeepers grouped by operation size. Contrary to public perception, migratory operations did not have higher losses than those operations that did not move colonies. Commercial beekeepers identified Varroa destructor mites and queen failure as the top two contributors to colony mortality. Chapter 3 is an observational study that identifies risk factors using real-world data from commercial beekeeper operations collected by the Bee Informed Partnership’s Tech-Transfer Team. Colony inspection metrics that predicted colony health or survival included an estimation of the adult bee population, loads and signs of the parasitic mite V. destructor, spore loads of the microsporidian Nosema spp., and the continuous presence of a queen bee. Overall, this study provides a way to make management decisions based on the likelihood of a colony health outcome. Chapter 4 determines if a colony phenotype can be attributed to a poor-quality queen. The failure of the queen bee was identified by the surveys and the Tech-Transfer Team data as a major contributor to colony mortality. One sign commonly attributed to the failure of a queen is a poor brood pattern – i.e. the continuity of cells on a comb containing sealed pupae. This study had two objectives: 1) determine if a poor brood pattern was reliably associated with other measures of queen quality (2016 and 2017); and 2) determine if brood pattern was influenced more by factors associated with the colony environment or by the queens’ egg-laying capacity (2017). Although brood pattern was not associated with measures of queen quality, brood patterns improved after a queen with a poor brood pattern was introduced into a colony with a good brood pattern, suggesting that colony environment had a larger impact on brood pattern than the queens’ egg laying capacity. The results imply that brood pattern is not a reliable indicator of queen quality and factors other than the queen can influence brood pattern. Overall, these studies contribute to the understanding of commercial beekeeping and can inform management practices to increase colony health and survivorship.