It’s no secret: commercial beekeepers have seen historic honey bee declines this year, losing over 60% of their bee colonies since last summer, the U.S. Department of Agriculture reported. However, the mystery behind these colony collapses may now be solved.

According to new research released June 2 by the USDA’s Agricultural Research Service, varroa mites are responsible for these record-breaking commercial beekeeping losses. 

Researchers also found that varroa mites have become resistant to common mite treatments — another contributing factor to population declines.

While companies work to develop new miticides, beekeeping leaders called for a deeper look into how other environmental factors have led to an increase in viruses.

“This is a critical moment for honey bee health,” said Patty Sundberg, president of the American Beekeeping Federation, in a statement. “We can’t continue relying on a single line of defense against Varroa. These mites are evolving quickly, and our management tools must evolve just as fast. We also need to find treatments for these viruses and we await the release of how pesticide exposure and poor nutrition amplify the impacts from these viruses.”

The study

Varroa mites are an invasive parasitic mite native to Asia. They were first introduced to the United States in Wisconsin in 1987, and since then have quickly spread across the country. 

These mites pose significant harm to honey bees by feeding off the bees’ fat bodies and transmitting diseases like Deformed Wing Virus, which causes twisted and shriveled wings, bloated abdomens and other deformities.  

This weakens bee colonies, leading to a decreased lifespan and death. Several mite treatments have been developed over the years to kill off verroa mites, including fluvalinate, coumaphos and amitraz, created in the late 1980s. 

But by the late ‘90s, varroa mites had already become resistant to fluvalinate and coumaphos treatments. Now, USDA researchers are saying this has happened once again with amitraz, the most common miticide used by commercial beekeepers. 

For the study, researchers collected samples from six major commercial beekeeping operations in California in January after beekeepers started reporting record losses leading up to almond pollination season — the largest pollination event in the world. These operations managed roughly 184,000 colonies, 7% of all U.S. hives. 

When analyzing bee samples, researchers found that 78% of bees contained the Deformed Wing Virus and 72% of bee colonies had unusually high levels of Acute Bee Paralysis, another mite-vectored disease.

Researchers also analyzed 39 mites taken from these bee colonies, 100% of which had resistance genotypes to amitraz. Organizations like the Honey Bee Health Coalition saw this coming back in 2021 when it released its “Guide to Varroa Mite Controls for Commercial Beekeeping Operations.”

“Relying on off-label chemical treatments for Varroa control may have worked in the short term; however, the long-term risks to the beekeeping industry cannot be overstated. Chemical resistance has the potential to leave beekeepers with exploding mite populations and nothing to stop the surge,” said the guide.

In reaction to the USDA findings, Steven Coy, president of the American Honey Producers Association, emphasized the importance of integrated pest management and the development of additional treatments as mites become resistant to older miticides.

New treatments are already in the works. The U.S. Environmental Protection Agency proposed to register a new pesticide on May 29 that would target varroa mites. The pesticide contains the active ingredient vadescana, developed by Massachusetts-based company GreenLight Bioscience.

According to the EPA, vadescana is safe for bees, humans and the environment. The agency has opened up a 15-day comment period before a final decision is made, which ended on June 12. 

Honey bees are one of a few animal pollinators that are responsible for pollinating three-fourths (75%) of the world’s flowering plants and about 35% of the world’s food crops, reports the USDA. This equates to one in every three bites of food an individual eats.

(Liz Partsch can be reached at epartsch@farmanddairy.com or 330-337-3419.)