GUELPH – Despite tighter restrictions on antibiotics used in Canadian beekeeping, honey bee death rates are still rising.
A new study led by University of Guelph researchers, published in Nature Sustainability, is the first large-scale project to assess antibiotic usage trends and their impact on honey bee health in Canada.
The withdrawal of antibiotics following recent regulation changes was one of the top predictors of honey bee overwintering mortality – a result that surprised lead author Dr. Brendan Daisley.
“You’d assume the lessening of antibiotics might be associated with improved health outcomes, especially since antibiotics are so overused,” says Daisley, a postdoctoral researcher in the College of Biological Science.
“But without effective alternatives, it seems the bees have developed a dependency on them.”
Using national survey data, researchers investigated more than 700,000 honey bee colonies per year between 2015 and 2023.
Colony losses varied by province, but overwintering mortality rose from an average of less than 20 to over 40 per cent, even as antibiotic usage halved, decreasing from approximately 50 to 25% nationally.
During the period studied, a new framework in 2018 put forth by the World Health Organization (WHO) and adopted by U.S. and Canadian agencies decreased over-the-counter access for certain beekeeping antibiotics.
This was done to address antimicrobial resistance (AMR) — the rising resistance to antibiotics that makes infectious diseases more difficult to treat.
AMR is one of top 10 public threats facing humanity, according to WHO.
“We didn’t know the repercussions of these global changes in antimicrobial stewardship,” Daisley says.
“But it shows one of the most important drivers of honey bee mortality rates is likely infectious disease, and the imbalance between ‘bad’ and ‘good’ microbes.”
Daisley examined honey bees’ entire bacterial community, known as their microbiome, as a way to assess their health.
“It’s a catch-22 – we know antibiotics are very useful for controlling disease outcomes, but they also disrupt the microbiome and do not distinguish between harmful and beneficial bacteria,” says Daisley. “We could be experiencing a microbial apocalypse in front of our eyes.”
The findings are a major breakthrough in microbiome research, he says, and may help explain record losses of the world’s bee colonies.
In addition to antibiotic usage, researchers identified another unexpected predictor of honey bee mortality: nitrogen dioxide (NO2), a common air pollutant from diesel exhaust.
NO2 degrades floral odours and disrupts the bees’ ability to forage, researchers say, which could be contributing to colony loss.
“It’s all interconnected, and in my opinion, all links back to microbial ecology and the microbial homeostasis of pollinators,” Daisley says.
