No correlation between natural mite fall and Varroa levels

Resistant bees, mite fall, and Varroa level

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Natural mite fall has been used to detect the presence of varroa mites in bee colonies. If this occurrence increases over time, it is considered to indicate an increased total number of mites in the bee colony. It is commonly believed that once a certain number of fallen mites—without prior treatment—has been reached, the mites must be controlled with miticides. 

The Varroa level measures the number of mites per 100 adult bees, i.e., a percentage. It is useful during the part of the season when normal (maximum) brood rearing occurs. Under our conditions in Central Sweden, this is typically from May to mid-August. It can be measured by alcohol washing of 1 dl of bees (approx. 300 bees) using a so-called shaking jar. This can be used to show how high the varroa level is, and how the level may develop over time during the brood season. A certain varroa level can be used as a measure of when it is considered that mitiicide treatment should be carried out.

Two Different Methods for Counting Mites

These are two different methods for counting mites from, and within, a colony. Both methods can be used to establish a basis for determining how to achieve treatment-free beekeeping. Neither of these methods measures the total number of mites in a bee colony.

Remember, neither of these methods to count mites measures the total number of mites in a bee colony.

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It is important to remember in this context that there is no specific threshold for the number of mites in a bee colony that determines whether there are too many in a colony. There are too many mites when you observe several bees with damaged wings on the hard board in front of the hive entrance. At any given time, there could be, for example, a total of 3,000 mites in a bee colony, or even more, without there being too many.

There are too many mites in a colony when, in the morning, there are more than just a few bees with damaged wings on the hard board in front of the hive entrance.

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Count the mites!

Natural mite fall (mite drop), used by British beekeepers, is used for example for the purpose of achieving Varroa resistant bees. It is described by Steve Riley in his book “The Honey Bee Solution to Varroa.” It can be ordered here: https://www.northernbeebooks.co.uk/products/the-honey-bee-solution-to-varroa-riley

You can listen to a lecture by Riley (you can avoid the Swedish subtitles) here: https://varroaresistens.se/steve-riley-transitioning-to-varroa-resistent-colonies-27-04-2026/

You can read about his method on my blog here: https://www.elgon.es/diary/?p=416888

and here: https://www.elgon.es/diary/?p=416905

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You can listen to (and read Swedish subtitles) lectures by British experts on varroa-resistant bees here: https://varroaresistens.se/

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Measuring varroa levels is the method many people in Sweden use to count mites in order to make informed decisions about selecting breeder colonies and determining whether to control varroa with chemicals. This is the method we used in Hallsberg to achieve treatment-free bees. At that time, we used thymol and no other treatment. The method is described here: https://www.elgon.es/varroalevel.html

In my opinion, measuring the varroa level as we have done it is the least labor-intensive method.

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Higher natural mite fall sometimes observed in bee colonies with treatment free queens

Beekeepers have been purchasing queens from us in Hallsberg for many years. Some have tested them in their apiaries without decreasing the use of miticides. Others have stopped treating colonies in which these queens have been introduced. This is especially true when queens have been replaced in all colonies within an apiary. The number of colonies in such an apiary has varied from a few to several. The distance to other types of bees has ranged from less than 1 km to several kilometers. I am not aware of any case where stopping varroa treatment under these circumstances has not gone well. I usually recommend a minimum of 2 km (2–3 km, 1.5 miles) to other types of bees.

Varroa-resistant colonies can sometimes result in unexpectedly high natural mite fall. This is due to intense hygienic behavior as mites are purged.

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Once in a while a beekeeper has contacted me to ask why there has been such a high natural mite fall in September in the very colony that received an Elgon queen in July. There are several ways to understand why this might happen.

Varroa-resistant bees are more hygienic

Varroa-resistant bees are more hygienic than non-varroa-resistant bees — in fact, I would say much more hygienic. Bees in varroa-resistant colonies identify brood infested with varroa mites and remove such brood to varying degrees, depending on how busy they are with various tasks throughout the season. 

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When a varroa-resistant queen is introduced into a non-resistant colony, it takes about three weeks after the queen has been fed to begin laying eggs, after she has been released from the introduction cage in the new colony, when her worker bees begin to emerge from eggs the new queen are laying. Therefore it will pass at least one month after introduction that one can expect the new queen and her worker bees to begin effectively clearing mites from the colony, provided the colony is not occupied with other labor-intensive tasks, such as collecting nectar from a plentiful nectar flow.

In that case, one can expect a comparatively higher down fall, especially if the other colonies in the apiary are not resistant. 

One Year of Mite drop in Resistant Colonies

Steve Riley measured the daily natural mite fall (without miticides) over the course of an entire year in a varroa-resistant colony. For most of the time, the mite drop was about 5 mites per day. The bees were constantly busy removing some of the Varroa. He noticed that, especially during late fall and winter, the daily mite fall became significantly higher (about 25) only to drop back down to about 5 per day after a period.

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I examined the daily mite fall in a dozen of my Varroa-resistant bee colonies during late fall and winter 2025–26.

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This led me to examine a number of colonies of my untreated bees and then planned to conclude with a test of the varroa level. The shaking box test (varroa level test) was conducted in mid-May when the apple blossoms began to bloom. This was the time I had previously determined to yield the most reliable varroa level reading for selecting breeder colonies during the years I regularly measured varroa levels. I hadn’t needed to do this for the past 5 years, as only a few wing-damaged bees had been observed on the hard board in front of the hive entrance, now that my entire apiaries have been treatment-free for at least 5 years. Most of them has been treatment-free for even longer.

I then conducted a varroa level test in these colonies in May.

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I conducted the first natural mite fall test over a few days in early November 2025 on about a dozen of my resistant colonies at various apiaries. All my colonies have been treatment free for 5-10 years. The daily mite drop varied between 5 and 25. One colony recorded as much as 45 per day. These values are thus what I would call the peak values for daily winter mite drop during the very active winter hygienic activity culling mites in the tested colonies. Compared to Steve Riley’s resistant colony regarding winter culling, his figure for peak mite fall was 25.

It should be noted that all my colonies are Varroa-resistant, but significantly stronger, bigger bee population. His colonies have roughly one British Standard box for brood chamber, while my colonies have about 2.5 this size for brood chamber. He also makes a split together with the queen — an artificial swarm — every year. According to him, my “normal figures” should be adjusted upward to a comparable degree. Perhaps that is the case. 

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No bees with damaged wings

It is worth noting once again that no bees with damaged wings were observed among my bees throughout 2025, nor in 2026, nor throughout the 2020s (with the exception of a couple of colonies in which I replaced queens without treating for the mite), despite—yes, I would argue, thanks to the absence of chemical treatment, both so-called organic and synthetic. My impression from these observations is that the bees become more robust with each passing year without chemical treatment, provided they are hygienic enough to sufficiently rid the colony of mites.

I did not observe any bees with damaged wings in any of my colonies in 2025 or 2026. And just a few in the years from 2020.

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The 45-colony received a new queen in 2025 after producing a poor harvest for two years, but it had nevertheless gathered 20 kg of honey for the winter-room, and ensuring a strong colony for overwintering. This year looks more promising. As a beekeeper, you have to do what you’ve always done: replace those who don’t meet expectations.

After the winter mite cull, all colonies recorded a daily mite fall of approximately 5 mites, as did Riley’s resistant colony. Some of my colonies had relatively low peak figures. Perhaps this can be interpreted as meaning they were more consistently active with culling throughout the year. And figures around 5 (with slight upward variations for some, i.e., more culling activity at times) in daily mite fall for the rest of the year indicate fairly steady “maintenance culling.” 

Non-resistant colonies that have reached a daily fall of 5 are usually interpreted as needing some form of chemical control, whether ecological or synthetic. They typically do not exhibit a cleansing behavior that has any significant impact on reducing the varroa population in the colony.

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The Varroa mite level test compared to natural mite fall

In mid-May 2026, the Varroa mite level was measured in the test colonies. This was done using the EasyCheck shaking jar, which is estimated to capture nearly 100% of the mites attached to the bees. The Varroa level is calculated as the number of mites per 100 bees, i.e., as a percentage (%). The number of bees in the test sample is calculated to 300 bees per deciliter of bees. The Varroa level varies slightly on each frame of bees. Therefore, it is advised to shake bees from 2–3 frames near the brood (but not brood frames) into a plastic tray and return the excess bees. Even so, one must expect that the sample will not provide a completely accurate value. A compromise must be made between achieving the greatest possible accuracy and avoiding excessive labor. Otherwise, one will not have the energy to continue. The described approach has provided a methodology and decision-making basis that has advanced the work of selecting varroa-resistant bees relatively quickly—in 5–6 years—even though project apiaries and mating sites are not completely isolated. Perhaps this has actually been an advantage, leading to greater genetic variation within each colony. This is believed to result in more resilient bees.

In Varroa resistant bee colonies I see no correlation between natural daily mite fall and the the Varroa level — the percentage of mites on adult bees — during the brood season.

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Average varroa mite level of 0.8%

The May test of varroa mite levels in the test colonies I examined yielded values that were, to my surprisingly low, except in one colony, which was at the threshold for treatment (the threshold that was used during the development of varroa resistance), with 9 mites per 300 bees (3% varroa mite level). The others ranged from 0 to 4 mites per 300 bees (0 – 1.3 %). All colonies combined yielded an average varroa level of 0.8%. 

No correlation

The results show no correlation whatsoever between daily mite fall and varroa levels in varroa-resistant bee colonies. We believe the reason is temporary increases in daily mite fall due to increased hygienic activity to remove mites from the colony.

The Varroa level monitoring is relevant during the normal to high brood rearing period, which in our area is from mid-May to mid-August. The first count is conducted here in mid-May to assist in selecting which colonies to breed from and which should have their queens replaced. This is relevant regardless of the degree of varroa resistance the bee colony has achieved. Ideally, no treatment should have been administered in the preceding fall or winter.

Here in Hallsberg, our experience with developing treatment-free bees has been limited to the use of thymol. See a description here: https://www.elgon.es/gradualresistance.html We have never used organic acids. We do not know if they are effective in developing varroa resistance this way. Anyone with such knowledge is welcome to share it with us.

Riley’s Method

If you wish to use daily mite fall as a selection method for breeding for Varroa resistance, Steve Riley recommends measuring the total mite fall over a 90-day period, approximately February 15–April 15, and selecting the colonies with the lowest mite counts for breeding. The colonies should be roughly equivalent in strength. Colonies that deviate significantly in a negative direction (higher mite count) are removed from the project apiary. New queens are mated in the project apiary.

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Accelerate progress toward Varroa resistance

You can accelerate the work toward treatment-free bees by acquiring at least few queens from areas that are treatment-free. The fastest way is to acquire 2–3 splits from such an area and have no other bees in the apiary where these are placed. You can also place just a small number of colonies in a separate apiary. Colonies in which the queens have been replaced with those from treatment-free apiaries. 

Speed up your work with treatment-free bees by acquiring a few queens from areas that are treatment-free.

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It’s a definite advantage to have other types of bees at least a few kilometers away. It actually doesn’t matter much if there are a few matings with non-resistant drones, considering that a queen mates with an average of 20 drones. In practice, this has proven to be true. Of course, it’s helpful if other types of bee colonies located a few kilometers away are at least friendly. As you establish more treatment-free colonies, you can expand the area with such colonies if you wish, for example, in collaboration with other beekeepers.