Reviving Amitraz: The USDA's Plan to Beat Resistance-Proof Varroa Mites

For more than a decade, amitraz was the treatment beekeepers could count on. The active ingredient in Apivar strips, it was easy on bees and queens, forgiving of timing mistakes, and reliably killed better than 90% of the varroa mites in a colony. That era is ending, and the reason is written into the mites themselves.

Why amitraz is failing

The 2024-2025 season was the worst on record for U.S. commercial beekeepers, who lost more than 60% of their colonies. When USDA scientists screened the mites behind those losses, the picture was grim: the varroa they tested had broadly developed resistance to amitraz, and had spread deformed wing virus into nearly every commercial operation sampled. (We covered the full fallout — record losses, the threat to the Beltsville bee lab, and a hopeful signal from Southern California — in our Spring 2026 bee health update.)

Resistance works the way it always does. Use one chemistry hard enough, for long enough, and the few mites that survive it become the ones that breed. Do that across a continent for fifteen years and you eventually select for a population that shrugs the treatment off. Amitraz did not get weaker; the mites got tougher.

The USDA's clever workaround

Here is where it gets interesting. Instead of hunting for an entirely new miticide — a slow, expensive, decades-long process — a team at the USDA's Agricultural Research Service is trying to make amitraz work again by attacking the mite's defenses directly.

In research published in February 2026, entomologist Julia Fine and colleagues at the ARS Pollinator Health Research Laboratory in Davis, California — working with UC Davis and ARS labs in Beltsville, Maryland and Baton Rouge, Louisiana — tested amitraz paired with a second compound: an inhibitor that blocks the mite's natural detoxification machinery.

The idea is elegant. Resistant mites survive amitraz partly by breaking it down or pumping it out before it reaches a lethal dose. Switch off that detox process and the pesticide accumulates inside the mite to the toxic levels it used to reach on its own. In the lab, the combination "increases amitraz toxicity and was even effective against amitraz-resistant mites."

As the researchers put it, better amitraz formulations "can decrease the need for additional treatments, lower the selection pressure on the mite population" — in other words, kill more mites with less chemical, and slow the evolution of the next wave of resistance.

The catch: this is a lab result, not a product

It is worth being clear-eyed. This is promising early-stage research, not a strip you can buy this fall. There is a long road from a laboratory assay to a registered, field-ready treatment proven safe for bees, queens, and honey. It may get there; it may not. Either way, it will not help the colonies you are trying to carry into this winter.

So treat the news as what it is: encouraging evidence that the resistance problem is solvable — and a reminder that the fundamentals still fall on you.

What to actually do right now

1. Stop leaning on a single chemistry. If amitraz (Apivar) has been your only tool, that is exactly the pattern that breeds resistance. Rotate. Our varroa treatment guide walks through oxalic acid, formic acid, and thymol and when each one fits.
2. Monitor, do not guess. Do an alcohol wash or sugar roll and turn the raw count into mites per 100 bees with the free varroa mite calculator — it also tells you whether your seasonal threshold says to treat.
3. Mind the calendar. The single most important treatment of the year is the late-summer one, as the winter bees are being reared. More on that in our late-summer mite guide.
4. Consider local genetics. Queens bred from survivor stock and locally adapted lines carry more of the mite-resistant behavior researchers keep finding in the wild. It is not a silver bullet, but it stacks the deck.

Amitraz may yet get a second life. Until it does, the beekeepers who keep their colonies alive will be the ones who monitor honestly, rotate their treatments, and hit the late-summer window on time.

Sources: USDA Agricultural Research Service, "Finding More Effective Treatments in the Fight Against Varroa Mites" (February 2026); USDA ARS commercial colony-loss and amitraz-resistance findings, 2025.