Analysis of pathogens associated with winter colony losses in Canada.
Pernal SF, Borba R, Hoover SE, Currie RW, Guarna MM, Giovenazzo P, Zayed A, Foster LJ (2022) Analysis of pathogens associated with winter colony losses in Canada. 47th International Apimondia Congress, pp. 42-43, 24-28 Aug 2022, Istanbul, Turkey.
Canadian beekeepers report that high pathogen/parasite infestation levels, poor queen quality and severe weather conditions are the leading causes of elevated wintering losses. In order to replenish annual losses or maintain their operations, beekeepers in Canada face a unique and difficult situation for purchasing new queens or package bees. Scarce local supply drives local producers to import approximately 300,000 queens and package bees each year, predominantly from foreign sources. This large-scale importation of stock may contribute to the introduction of undesirable pathogens or genetics, and supply bees that have not been selected to survive and prosper in northern temperate climates, thereby influencing wintering success.
Honey bees act as a host for a multitude of pathogens and parasites. Nevertheless, the interactive effects that many of these pathogens, endoparasites and ectoparasites have on colony wintering success remains poorly understood. In order to better understand these interrelationships, we studied colony health and wintering success as a part of a national-scale study in Canada. In 2016 and 2017, we sampled 1025 and 520 colonies, respectively, across five Canadian provinces. During each experimental year (May through April), we collected pre-winter phenotypic data (fall colony weight and cluster size), and samples for pathogen analysis (Nosema spp., Lotmaria passim, DWV-A, DWV-B, BQCV, SBV, and phoretic loads of Varroa destructor) from colonies in all locations to investigate the main drivers of colony winter mortality. We also studied colonies wintered outdoors, as well as those wintered inside specialized wintering facilities. Although winter mortality was statistically similar between 2016 and 2017, indoor-wintered colonies had greater survival than those wintered outdoors (92% vs 77%). Irrespective of wintering method, consistent influences were seen across both experimental years, based on logistic regression modelling. Elevated levels of DWV-A, DWV-B, BQCV and fall phoretic mite loads increased the risk of colony death during winter, whereas higher fall colony weights, larger cluster sizes and increased sealed brood areas exerted positive influences on survival outcomes.