Lesson 56: When to Treat, and With What
Mite thresholds, and the menu of control methods from gentle to strong
You've counted your mites (lesson 55). Now: is it time to act, and what should you do? This is where sources differ, and we'll show you where. The principles, though, are agreed: act before mites reach damaging levels, use gentler methods where they work, rotate treatments, and always check that what you did worked.
The threshold: when to act
A treatment threshold is the mite level at which a colony is at risk and you should act.
Sources differ on the number:
| Source | Treat when (alcohol wash or sugar shake) | Sticky board |
|---|---|---|
| Honey Bee Health Coalition (9th ed., 2026) | 1 or more per 100 bees (1%) in winter and spring build-up; 2 or more per 100 (2%) at the summer peak and fall decline | Use only as a quick check |
| Penn State Extension | Keep mite levels below or around 2 per 100 | — |
| USDA Agricultural Research Service | 3 or more per 100 bees (3%) | More than 30 mites per day |
What this means for you: the newest guidance (Honey Bee Health Coalition, 2026) is stricter: act earlier, at lower numbers. Mite counts underestimate the real total (many mites are hidden in brood), and colonies can go downhill quickly. When in doubt, act on the lower number, and act promptly. Thresholds can also vary by region, so ask your state or university extension apiculturist, or your bee club. (Your weekly issue uses the threshold noted in your Seasonal Guide.)
Two more rules: - If a colony is over threshold, treat promptly. A delay can cost the colony. - Resample after treating. After a successful treatment, an alcohol wash should usually show under 2 per 100.
The options, from gentle to strong
Control methods are often pictured as an IPM pyramid (lesson 53): use the base first, the top only when needed.
Cultural methods (prevent mites building up)
- Mite-resistant bee stock: Russian bees suppress mite reproduction; VSH and hygienic bees remove infested brood (lessons 15 and 83).
- A brood break: caging or removing the queen for about three weeks (or letting a colony requeen itself) means no new brood for mites to breed in. All the mites end up on adult bees, where they can be groomed off or treated. It can also give you a young queen for winter.
- Small-cell comb: some beekeepers use it; its effect on mites is debated in research, but it doesn't harm bees.
Mechanical methods (remove mites)
- Drone brood removal: add a drone comb frame. Mites crowd into the drone cells, then you remove the frame after it's capped, before the drones emerge, freeze it or scrape it, and return it. It slows mite growth, but usually isn't enough on its own.
- Screened bottom boards: mites that fall off bees drop through and can't climb back. Helpful, but mite levels often still reach thresholds, so combine with other methods.
- Powdered sugar dusting: makes bees groom off mites. Labor-intensive, and won't control mites on its own.
"Soft" chemical treatments (naturally derived)
These leave little or no residue in wax. Try them first when chemicals are needed: - Formic acid: reaches mites under the cappings. Temperature-sensitive: too hot (above about 85°F) can harm brood and the queen; too cold (below about 50°F) and it works poorly. - Oxalic acid (vapor or dribble): doesn't reach mites under cappings, so it works best when there's little or no brood, such as in winter or during a brood break. Overuse can harm bees. - Thymol (from thyme oil): works on mites on adult bees, not under cappings; temperature-dependent; can reduce brood, trigger robbing, and make bees more defensive; best combined with other methods. - Hop beta acids (HopGuard): generally safe during a honey flow per its label, but less effective than other soft treatments and needs repeat applications when brood is present.
"Hard" synthetic chemicals (last resort)
- Amitraz (Apivar): the most-used synthetic; generally effective, but mite resistance has been documented, so check that it's working.
- Fluvalinate (Apistan) and coumaphos (CheckMite+): mites are widely resistant, and residues build up in wax, which can harm bees. Penn State does not recommend them.
Newer options keep arriving. For example, in 2025 EPA registered a new, highly mite-specific active ingredient (a dsRNA product). Always check the current list of registered products (lesson 57).
Rotate to prevent resistance
Mites become resistant to a treatment used over and over. Rotate between products with different active ingredients over the year and from year to year, and use a different product in the fall than you used earlier in the year. Using only one product repeatedly has already made several products much less effective.
What to remember
- Act at the threshold. Sources differ: HBHC 1% (spring) / 2% (summer-fall), Penn State ~2%, USDA 3% (or 30+/day on a sticky board). When in doubt, use the lower number.
- Treat promptly when over threshold, and resample afterward.
- Gentle first: resistant stock, brood breaks, drone brood removal, screened bottoms. Then soft chemicals (formic, oxalic, thymol, hop acids). Synthetics last.
- Rotate active ingredients to prevent resistance; temperature and brood decide which product fits.
Quick check
- Your August alcohol wash shows 2.5 mites per 100 bees. Is that over threshold?
- Why does oxalic acid work best when there's little or no brood?
- Why rotate between different treatments?
Show answers
1. Yes by the Honey Bee Health Coalition's 2% late-season threshold (and near Penn State's), though under USDA's 3%. The newest guidance says act. 2. It doesn't penetrate brood cappings, and when there's no brood, all the mites are on adult bees where it can reach them. 3. Mites become resistant to a product used repeatedly; rotating active ingredients keeps treatments working.
Adapted from: Honey Bee Health Coalition, Tools for Varroa Management (9th ed., 2026); Penn State Extension, Methods to Control Varroa Mites: An Integrated Pest Management Approach (Underwood & López-Uribe, updated 2025); USDA Agricultural Research Service, When to Sample and Sticky Board; U.S. Environmental Protection Agency, EPA-Registered Pesticide Products Approved for Use Against Varroa Mites in Bee Hives.
Adapted from university Extension sources. Experienced Georgia beekeepers are reviewing these lessons. See something that doesn't match your experience? Tell us.