Learning from Winter Mortality

Thursday 1 September 2022

The Canadian Honey Council (CHC) has released their newest edition of quarterly HiveLights magazine. The CHC is a national organization that represents beekeepers across Canada. Reading HiveLights magazine is a great way to stay connected with the beekeeping industry at a national level, and is available to read on the CHC website. For Atlantic Beekeepers, joining your provincial beekeepers association includes the added benefit of receiving this magazine in the mail! In this week’s blog, we will highlight one article from the 2022 summer edition discussing the causes behind overwintering losses. 

Learning from Winter Mortality 

The Canadian Association of Professional Apiarists recently released the results of their annual overwinter loss survey. This year, the average loss across the nation was alarmingly high, at 45.5%, nearly doubling reports from the previous year (CAPA 2022). To mitigate losses in the future, it is important to look back and try to adapt management practices accordingly. This was the focus of research done in Ontario in 2008 supported by the University of Guelph, Ontario and the Ontario Ministry of Agriculture, Food and Rural Affairs (Guzman-Novoa et al. 2002). Though this research was from 2008, the results are valuable and applicable today.

(Guzman-Novoa et al. 2022)

To better understand the cause of winter losses, researchers in Ontario carried out a survey and field study focusing on factors that are commonly linked to overwintering losses. They focused on colony management practices, food stores, parasite levels, and colony strength, as these are commonly cited as cause for winter losses in Canada. Based on the responses of participating Ontario beekeepers, hive wrapping and Varroa mite treatments were the only two fall management practices included in the survey which had a significant impact on overwintering losses. Beekeepers who wrapped their hives had significantly lower overwintering mortality than beekeepers who did not wrap their hives. Similarly, beekeepers who treated for Varroa mites in the fall had significantly lower overwintering mortality than beekeepers who did not. Based on these results, the authors suggest these to be important management practices for lowering overwintering losses.

In the field study, the researchers quantified aspects of fall management that are frequently linked to overwintering losses and analyzed the relationship between these variables and the colony survivorship. This study showed that the varroa mite infestation levels, the number of frames of bees, and the quantity of in-hive food stores all significantly impacted the survivorship of a colony, in that order. Hives which survived had 3% Varroa mite infestation or lower and an average of 8 frames covered in bees in the fall. 

(Guzman-Novoa et al. 2022)

The results of this study align with the results of the CAPA overwintering survey for 2021-2022 in the Atlantic Provinces. In this report, Atlantic beekeepers indicated weak colonies in the fall, ineffective Varroa control, and starvation to be the number one causes of overwintering losses for the season (CAPA 2022). As such, these are important management factors to consider across Atlantic beekeeping operations as fall management begins. Some crucial steps to prepare for the upcoming winter will include, monitoring for varroa mite levels in hives and treating accordingly; assessing hive strength and combining weak hives; and feeding early to ensure the bees have sufficient food stores. 


Guzman-Novoa, Ernesto, et al. “Effect of Parasite Levels and Bee Population on Winter Mortality and Spring Build-Up of Honey Bee Colonies.” HiveLights. Summer 2022, 29-32.
Canadian Association of Professional Apiculturists Statement on Honey Bee Wintering Losses in Canada (2022). CAPA, 2022.

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