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Beekeeping
All Containers›Shop by use case›Beekeeping›Pests, disease and colony health›Treatment resistance and rotationShop all honey and bee products →
Colony health

Treatment resistance and rotation

By Dwight Davis, Founder

Updated

On this page6
Varroa has developed resistance to treatments that used to work, in the ordinary way that any population under selection does. Managing that is most of what integrated pest management actually means in practice.

Why it happens

Any treatment that kills 95 percent of mites leaves the 5 percent least affected by it to breed the next generation. Repeat that every season with the same product and you are running a selection program for mites that survive it.

Two things make it worse. Under-dosing, which leaves survivors without killing enough to matter. And treating on a calendar rather than on a count, which applies selection pressure in seasons when it was not needed at all.

Where it has happened

Resistance has developed most in the synthetic miticides, the pyrethroid and amitraz strip products. Those are the treatments that were easiest to use, used most often, and used on a schedule, which is exactly the recipe.

The organic acids and thymol products have held up better. They are harder to use, more sensitive to temperature, and they work by mechanisms that are less easily selected against.

Rotation

Rotate the chemical family, not the brand. Two products from the same class under different names are the same selection pressure. The families are organic acids, essential oil based, and synthetics, and rotation means moving between those rather than between labels.

In practice most programs use different tools at different points in the season anyway, because temperature and the presence of honey supers restrict what can be applied when. That seasonal constraint does some of the rotation for you.

What rotation is not

It is not using several products at once. It is not switching because the last one seemed weak without having counted before and after. And it is not a substitute for monitoring, because without a count you cannot tell resistance from a badly timed application.

A post-treatment count is the only way to know whether a treatment worked. That is one extra alcohol wash and it is the difference between managing resistance and guessing at it.

The non-chemical half

Drone brood removal, brood breaks from splits or requeening, and mite-tolerant stock all reduce the load the chemistry has to carry. None of them is sufficient alone and all of them lower the number of treatments a season needs, which is the actual mechanism by which resistance is slowed.

References

Penn State Extension. Honey Bee Management Throughout the Seasons; Methods to Control Varroa Mites. extension.psu.edu
USDA ARS, Carl Hayden Bee Research Center. Varroa monitoring and treatment. ars.usda.gov
Treatment products are regulated and the label is a legal document. It overrides anything on this page, including on dose, temperature and whether honey supers may be in place.