The mystery surrounding a mass die-off frustrates beekeepers and the bee industry
A parasitic varroa mite is visible on a dead bee in 2023 in College Park, Maryland. | Photo courtesy of AP Photo/Julio Cortez
Excerpt from the Sierra Magazine:
As the weather began to cool toward the end of 2024, Bret Adee, a beekeeper in South Dakota, discovered that his typically busy hives were no longer bustling. He was preparing to send them to California, where his bees help to pollinate almond groves. However, he was shocked to find that nearly three-quarters of his bees were gone.Â
âItâs heartbreaking,â he said. âYou feel like you've thrown your own life away.â
Adee is one of hundreds of beekeepers in the United States who lost over 60 percent of their colonies in late 2024 and early 2025. It was the nationâs worst-ever mass honeybee die-off and the second major population crash in the past two decades. The first took place in 2006â07.
Scientists from the US Department of Agriculture scrambled to find out what went wrong. Last June, the agency declared it had solved the mystery. Colonies had succumbed to viruses that were spread by the parasitic mite Varroa destructor. The harmful viruses included two strains of deformed wing virus that stunt and tatter beesâ wings and shorten their lifespan.
But Sierra has learned from university researchers that the hives were also exposed to a cocktail of agricultural pesticides that may have played an important role in weakening bee health. The USDA has not yet published the pesticide data.
The scientific debate raises larger questions about the role beekeepers might be playing in the collapse, and whether commercial pesticide companies should be held accountable. It also highlights that other factors, such as climate change, are wreaking havoc in hives.
In early 2025, the USDA took samples from 113 coloniesâsome of which were weak and dying; others were strongâwithin six large commercial beekeeping operations. Researchers also examined 39 mites from five of the beekeeping operations and found that all were resistant to amitrazâa pesticide widely used by beekeepers to manage the varroa mites. The agencyâs researchers concluded that amitraz applications did not effectively control the mites.
âThese viruses are responsible for recent honeybee colony collapses and losses across the US,â said a USDA press statement from June 2025.
âAmitraz has been suspected of losing efficacy after decades of heavy use, and our results strengthen this claim,â wrote the USDA researchers in a study that was published in February in the journal PLOS Pathogens.
These findings have enraged beekeepers who feel that the USDA was trying to pin the blame on them for poor bee husbandry and for overusing amitraz in ways that contributed to the development of resistance in mites. If beekeepers rely just on amitraz, year after year, then the mites can more quickly develop resistance than if they switch mite treatments with other chemicals and methods. But some beekeepers who didnât use amitraz or who alternated its use say they also lost many colonies.
Steve Ellis, a commercial beekeeper in Minnesota and president of the Pollinator Stewardship Council, an industry group, said that he finds the USDA statements âmisleading and inappropriate.â
Some beekeepers said that they felt the study was too small to be representative of beekeeping across the country. They also feel that the researchers drew premature conclusions because the analysis did not include data from tests on agricultural pesticide residues in bee colonies. Agricultural pesticides such as neonicotinoids can harm bees, analyses show. A few bee professionals have wondered if pesticide poisoning or contamination contributed to the die-off.
