Science shares research that identifies a massive killer of honeybees — a virus that’s carried by pesticide-resistant mites:
U.S. beekeepers had a disastrous winter. Between June 2024 and January 2025, a full 62% of commercial honey bee colonies in the United States died, according to an extensive survey. It was the largest die-off on record, coming on the heels of a 55% die-off the previous winter.
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According to a preprint posted to the bioRxiv server this month, nearly all the dead colonies tested positive for bee viruses spread by parasitic mites. Alarmingly, every single one of the mites the researchers screened was resistant to amitraz, the only viable mite-specific pesticide—or miticide—of its kind left in humans’ arsenal.
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“There is a lot at stake,” says Danielle Downey, the executive director of Project Apis m., the nonprofit that conducted the bee die-off survey. USDA did not provide comment on its research to Science after multiple inquiries spanning nearly 3 weeks, with one spokesperson citing a need “to move [the request] through agency clearance.”
Miticide-resistant varroa mites have been a growing issue for beekeepers for years, so much so that breeders have sought to develop mite-resistant bee varieties. Since the 1980s, the parasites have evolved global resistance to at least four major classes of miticide. Unfortunately, effective new compounds are notoriously difficult to develop, and amitraz represented one of the best remaining treatments. But the preprint suggests amitraz could soon fall by the wayside.
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A team led by Jay Evans and Zachary Lamas, both bee researchers at USDA’s Bee Laboratory in Beltsville, Maryland, collected dead bees from 113 affected colonies from across the U.S., as well as samples of wax, pollen, honey, and—when possible—any parasites. The samples were taken to national bee labs in Beltsville and Baton Rouge, Louisiana, where researchers extracted DNA and RNA and analyzed it for snippets of viral or bacterial genetic material. They also sequenced DNA from the recovered varroa mites and looked for genes related to miticide resistance.