For Ian Steppler, a commercial beekeeper near Deerwood, Man., managing varroa mites is a persistent battle.

The invasive parasite, which has plagued North American beekeepers since the late 1980s, continues to escalate its toll on honeybee colonies across the globe. They’ve become a consistent contender among the top four causes of winter bee loss in Canada, as noted by the Canadian Association of Professional Apiculturists.

In Manitoba, varroa topped the list in 2022, when the province saw a staggering 57.2 per cent colony loss, according to the association’s annual survey.

“Varroa mite is a huge, probably our number one problem in Manitoba, right across Canada and North America,” Steppler said. “Actually, it’s a worldwide problem right now.”

Why it matters: Weakness and disease caused by varroa mite infestation can devastate honeybee hives, and as control from go-to products becomes less effective, Prairie beekeepers are searching for new solutions.

The mites weaken bees by feeding on their fat stores, and also carry viruses. Steppler says the problem seems to be worsening.

Chemical control, meanwhile, is becoming more complicated. It has been several years since beekeepers noticed that one industry standard, Apivar, did not always deliver the same control. Varroa mites had already developed resistance to other products, and worry bloomed that the same was happening with Apivar.

That concern launched resistance testing and product trials by organizations including the Manitoba Beekeepers Association.

In early 2022, then-provincial apiarist Rhéal Lafrenière warned producers to broaden their varroa control toolbox and consider multiple avenues of attack.

Enter organic acids

Some now use formic or oxalic acids or thymol-based products, but those products have a learning curve, experts note. If used improperly, the producer can cause a wreck.

“These alternative treatments … require certain conditions for them to work effectively,” Steppler said. “Formic acid, for example, is a very volatile substance. If it’s too hot, it’ll volatilize very quickly and could potentially kill your colony. But if it’s too cold, it doesn’t volatilize enough … so there’s a very small window that you can use this product.

“It’s like a double-edged sword. We have to control these mites. Otherwise, the mites will bring down the colony due to disease.”

The alternatives, however, risk running afoul of the products’ slim margin for error.

In 2022, Lafrenière pointed to other challenges with organic acids. The short window for use can result in low rates of bee contact. Some of these products are so hard on bees that honey production can be affected, depending on time of application.

Avoiding damage

Beekeepers rely on a combination of provincial guidelines, hands-on experience and educational resources to mitigate risks.

Provincial guidelines state that regular inspections are crucial in the fight against varroa mites, especially during spring and fall. Producers should monitor infestation levels and verify the effectiveness of treatments.

Colonies should ideally maintain mite levels below one per cent during the spring and between one and two per cent in late summer when brood is present, the guidelines state. As brood production extends later into the fall, which Manitoba beekeepers have noted, consistent monitoring is even more critical.

In spring 2024, provincial apiarist Derek Micholson said warm weather in the previous autumn may have reduced varroa control.

“The beekeepers are kind of relying on the colonies to shut down brood production so these treatments can work, but that’s not happening,” he said at the time.

“Then these treatments don’t work as well. These hives go into the winter with higher varroa mite loads and then, if you have these big temperature swings over the winter and brood being produced, then the varroa mites are also reproducing more.”

To reduce the risk of mites developing resistance to treatments, beekeepers are urged to rotate between different control products. Alternating between synthetic chemicals and organic options can help maintain efficacy and protect colony health, the guidelines add.

Mechanical hindrances like screened bottom boards can limit mite re-entry into the hive, according to guidelines. Those won’t be effective alone, but can complement chemical treatments or other solutions, such as mite-resistant bee genetics.

If opting for those, the province warns, beekeepers should clear debris from the bottom boards to dodge other pests like wax moths. It also notes the precise environmental requirements when using organic acid or thymol-based alternatives.

New answers needed

Environmental unpredictability further complicates the fight against varroa mites, said Rod Scarlett, executive director of the Canadian Honey Council.

“There’s so many variables. Weather is a variable, rain … there are many variables out there for treatment. You have to have a full tool kit out there.”

According to Manitoba Agriculture, combining treatments with good hive management, such as resistant bee genetics or employing screened bottom boards, can provide year-round benefits.

Steppler said more investment in safer and more effective solutions are also needed.

“We just need more attention towards helping us use these products … so they maybe don’t hurt our colonies as much.”

One promising development is an RNA-based treatment now undergoing trials in Manitoba.

“We’re testing a new RNA product for mite control, and it seems to be … almost benign,” Steppler said. “It leaves no residue in the wax, which is one of the problems with chemical treatments.”

While the trials show potential, the product is not yet approved, though the need is urgent.

“We need new chemicals, new ways to address the varroa problem, whether it be organics or hard chemicals,” said Scarlett.

Matthew Polinsky is program lead for the Manitoba Beekeepers’ Association’s Knowledge and Research Transfer Program (KRTP), designed to help the industry manage varroa mite issues and other challenges.

Polinsky has worked on the RNA product trial, a collaboration with the product’s manufacturer, U.S.-based GreenLight Biosciences Inc., for the last two years.

GreenLight has applied for product registration in the U.S. Approval in Canada will require testing with programs like the KRTP, Polinsky said.

“(We’re) seeing how well it works and if there’s efficacy there, and from there, the company can either decide they want to go ahead and apply to register with the Canadian Pest Management Regulatory Agency.”

Keeping an eye on varroa

The research program is also helping producers keep tabs on the issue. Its bee health monitoring program takes samples of bees, tests for pathogens and helps with grower monitoring.

“We work with people to look at and to make sure that they have an adequate picture of what’s actually going on, because varroa is one of those things that can almost seem invisible until it’s such a problem that your colonies are collapsing,” he said. “It’s easy to get caught off guard.”

The KRTP’s acaricide resistance testing also continues. Varroa-infested bees are exposed to a treatment. The program then observes how many, if any, of the varroa population shows resistance to the treatment.

Samples of varroa mites are also sent to the National Bee Diagnostic Centre in Beaverlodge, Alta.

“They have the means to do genetic analysis to check for mutations associated with resistance. This is a relatively new technology, and so it’s great that the KRTP exists in Manitoba and is able to tap into those collaborations for advancing our knowledge on mite populations across our province,” Polinsky said.