Checking for Varroa Mites: A Late-Summer Guide for Beekeepers

For many beekeepers, honey harvest is one of the most rewarding times of the year. Frames are heavy, supers are coming off the hives and months of work by both the beekeeper and the bees are finally paying off. But while you're thinking about honey, there is something else you should be thinking about: Varroa mites.

Late summer is one of the most important times to monitor Varroa destructor, especially for beekeepers in Wisconsin and other northern states. Colonies are beginning to raise the long-lived bees that will carry them through winter, which makes keeping mite levels under control especially important. The University of Minnesota Bee Lab recommends controlling mites in late summer before large numbers of winter bees are produced. (beelab.umn.edu)

Should You Check for Varroa Mites During Honey Harvest?

Yes. Honey harvest is an excellent time to check your mite levels.

A colony can look strong, produce plenty of honey and still have a significant Varroa population. Mites reproduce underneath capped brood, so most of the problem can remain hidden during a normal hive inspection. (extension.psu.edu)

For new beekeepers, this is an important lesson: you cannot reliably determine a colony's Varroa level simply by looking at the bees. Testing gives you real information.

Why Late-Summer Varroa Control Matters

Throughout spring and summer, honey bee colonies expand and raise large amounts of brood. Unfortunately, that brood also gives Varroa mites more opportunities to reproduce. Female mites enter brood cells shortly before they are capped, reproduce alongside the developing bee and emerge with new mites when the adult bee comes out.

This becomes especially important in August and September as colonies begin producing their winter bees. Unlike summer workers that may live only several weeks, winter bees must survive for months. Varroa mites weaken developing bees and are associated with the transmission of viruses that can shorten their lifespan. (extension.psu.edu)

In other words, the bees that carry your colony through January are being produced long before January arrives. Managing mites now can have a major impact on winter survival.

How to Check a Beehive for Varroa Mites

One of the most reliable ways to estimate your colony's mite population is an alcohol wash or soap wash using approximately 300 adult bees, or about ½ cup of lightly packed workers, collected from brood frames. (honeybeehealthcoalition.org)

First, locate your queen so she isn't accidentally included in the sample. Collect worker bees from one or more brood frames, place them into an appropriate testing container and complete the wash according to the method you're using. Count the mites that fall from the sample and calculate the approximate infestation percentage.

For example, six mites from a 300-bee sample equals roughly a 2% mite level.

There is no single treatment threshold that fits every beekeeper or region, but the University of Minnesota recommends maintaining mite levels below 1% when possible and indicates that treatment may be warranted when levels rise above approximately 2%. (beelab.umn.edu)

Three Varroa Treatment Options for Late Summer

If your test shows that treatment is needed, the next step is choosing the right product for your colony. The EPA maintains a list of registered Varroa-control products, and the treatment you choose should depend on factors such as temperature, brood levels and whether honey supers are still on the hive. (epa.gov)

1. Formic Pro — Formic Acid

Formic Pro can be particularly useful during late summer because it is labeled for use with honey supers on the hive in the United States. Formic acid also penetrates capped brood, helping reach mites that are reproducing underneath the cappings. (nodglobal.com)

Temperature is important. The manufacturer identifies a treatment range of approximately 50°F to 85°F, so Wisconsin beekeepers should check the forecast carefully before beginning treatment. Always follow the current label instructions for application, ventilation and colony requirements. (nodglobal.com)

2. Apivar 2.0 — Amitraz

Apivar 2.0 is an amitraz-based strip treatment that can be a good option once honey harvest is complete. The strips are placed within the brood area and remain in the colony for several weeks, allowing worker bees to come into contact with the active ingredient and distribute it throughout the hive. (veto-pharma.com)

Unlike Formic Pro, surplus honey supers intended for harvest must be removed before using Apivar 2.0. Because resistance to amitraz is also a concern, beekeepers should avoid relying exclusively on the same active ingredient year after year. (veto-pharma.com)

3. Apiguard — Thymol

Apiguard uses thymol, a naturally occurring compound found in thyme. The slow-release gel is placed above the brood area, where worker bees help distribute thymol throughout the colony. (vita-europe.com)

Apiguard generally works best in warmer conditions and is often a good post-harvest option in late summer or early fall. Honey supers intended for harvest should be removed before treatment, and temperature should always be considered when deciding whether thymol is appropriate for your colony.

Which Treatment Should You Choose?

There isn't one Varroa treatment that's best for every hive. Start by asking a few simple questions: Are honey supers still on? What will temperatures be during treatment? How much brood is present? What active ingredient did you use previously?

If honey supers remain on the hive, your options are more limited and Formic Pro is one treatment labeled for that situation. If harvest is complete, products such as Apivar 2.0 or Apiguard may also be options depending on conditions.

Varroa management works best as part of an Integrated Pest Management, or IPM, strategy. That means monitoring mite populations, using treatments when necessary, rotating treatment approaches when appropriate and verifying that those treatments actually worked. The Honey Bee Health Coalition updated its Tools for Varroa Management guide in 2026 with current monitoring and management information for beekeepers. (honeybeehealthcoalition.org)

Don't Forget to Test Again

Applying a treatment isn't the final step. Test again after treatment.

The goal isn't simply to say that you treated your hive; it's to know whether the treatment actually reduced the mite population. Mite levels can vary considerably between colonies in the same apiary, which is why each colony should be monitored individually.

Keeping simple records can also help. Note the date you tested, mite count, treatment used, treatment dates and your post-treatment mite count. Over several seasons, those records can become one of the most useful management tools in your bee yard.

A Strong Honey Harvest Doesn't Always Mean a Healthy Hive

One of the hardest lessons for a new beekeeper is that a hive can look fantastic in August, boxes full of bees, solid brood patterns and heavy honey supers, while still carrying a significant Varroa population.

So when you pull honey this season, don't make honey the only thing you measure.

Harvest the honey. Check your mite levels. Treat when necessary. Test again.

For Wisconsin beekeepers, preparing a colony for winter begins long before the first snowflake falls.

Frequently Asked Questions About Varroa Mites

When should Wisconsin beekeepers check for Varroa mites?

Varroa should be monitored several times throughout the season, but late summer is especially important because colonies are producing the bees that will carry them through winter.

Can you treat Varroa mites while honey supers are on?

It depends on the treatment. Formic Pro is labeled for use with honey supers present in the United States, while products such as Apivar 2.0 require harvestable honey supers to be removed. Always follow the current EPA-approved label.

What is the best way to test bees for Varroa mites?

An alcohol wash or soap wash using approximately 300 adult bees collected from brood frames is one of the most commonly recommended ways to estimate mite levels.

How many Varroa mites are too many?

Thresholds vary, but a level around 2%, approximately six mites in a 300-bee sampleis commonly considered a point where treatment should be strongly considered. Lower mite levels are preferable going into winter.

Should I treat if my hive looks healthy?

Don't make the decision based on appearance alone. A productive, strong-looking colony can still have a serious mite problem. Test first, then make your treatment decision based on the results.

Important: Varroa treatments are pesticides and must be used according to their current EPA-approved labels. Labels, registrations and recommendations can change, so always read and follow the label supplied with the product before treating your colonies.