Count mites

Increase varroa resistance

On November 15, 2025, we held the 7th annual varroa resistance conference in Hallsberg. The pleasant conference room in the parish hall near the Nordic region’s largest marshalling yard was filled to capacity. Around 60 beekeepers from almost all over Sweden gathered there. 

There are more and more lectures with different organizers in places other than Hallsberg. Try to keep track of how many treatment-free apiaries the lecturers have.

A year earlier, Professor Stephen Martin coined a phrase that is becoming more and more famous. 

“For the beekeeper, varroa resistance is simple, but for the researcher, it is complicated.” 

This is a good summary of what we are doing and what we hope for the future, also for the researchers. They are investigating how the ingenious bee colony works to solve challenges in many different ways.

For the beekeeper, it is enough to count the mites in some way, cultivate the colonies with the fewest mites, and replace the queens in those with the most. New queens are mated in project apiaries (their own or others’) that participate in the development of varroa resistance.

There are more treatment-free beekeepers in Sweden than one might realize. Not all of them came to Hallsberg. Their numbers are growing all the time. We need to exchange experiences and get tips from each other. In Hallsberg, we have long used small cell sizes (4.9 mm), at least in the middle of the brood comb. https://www.elgon.es/helpingresistance.html

In Hallsberg, the area with treatment-free beekeepers is growing. East, west, and north. It is starting up in areas further away. In Mölnlycke, there is a vibrant association that can also start offering queens. In the Ullared area, Varberg, there is a group that has been growing for several years and can offer queens and splits. 

Egon Andersson from Mölnlycke talked about how they work there, including their good contacts with the Swedish Board of Agriculture. Kent Evertsson from Västernärke talked about how to connect the area with the western part of Hallsberg. Magnus Kranshammar Ullared/Varberg shared how they help new beekeepers in the area with colonies and queens. Per Ideström talked about how he has expanded to more apiaries and how they manage with different distances to other apiaries. He also keeps in touch with other players in Swedish beekeeping.

Too much varroa?

This question has become relevant because it is not really clear what is meant by such a question. Some people think it is too many as soon as they see a mite. The beekeeping community’s response seems to vary. We discussed this question at the conference.

Most people believe that too many mites in a bee colony mean that there is a high risk that it will not survive the coming winter.

A basic answer to the question in the headline is NOT how many mites can be counted. It is not possible to measure the number in the colony directly. The number of mites on a drop board/tray may, for example, depend on whether the colony is good or bad at getting rid of mites.

A number must also be related to something else, such as the strength of the bee colony. What we may not often think of is that it is not the varroa mite itself that kills bee colonies, but viruses. Viruses that are closely associated with the varroa mite.

One such virus is DWV, Deformed Wing Virus. The answer to the question in the headline can be formulated as follows:

When you see worker bees with damaged wings crawling outside the hive entrance. 

More than two at the same time can often be the answer. This can be especially true when you are breeding bees but do not yet have treatment-free bees. A reading is made easier by placing a 0.5×0.5m hard board in front of the hive entrance.

The answer is based on experience gained in breeding for varroa resistance. It is an imprecise answer. It is a compromise that makes the observation easy to read but imprecise. A more accurate reading could require much more work. Many would soon become tire of it. It has been shown that this imprecise but easy-to-read observation is sufficiently accurate to provide a basis for decision-making. 

This number must also be put into relation to something else, such as whether the bee colony is treatment-free, partway there, or treated regularly to reduce the number of mites without consideration for increased resistance. If it is untreated, how many years has it been so, also has an impact. The more years it has been untreated, the more bees with wing damage can temporarily occur without the colony being affected. And the more mites can temporarily occur due to various reasons, such as drifting, robbery, etc. Virus resistance increases over the years. The amount of virus per mite and per bee decreases in a treatment-free apiary.

To make reading easier, place a hard board, 0.5×0.5m, in front of the hive. Check the board in the morning, preferably every 7-10 days.

If you have just started breeding for varroa resistance and see 1-2 bees with damaged wings on the hard board in front of the hive entrance, the right decision may be to treat the colony within a week to reduce the number of mites. In the breeding work that forms the basis for these reflections, thymol pads made of natural dish cloth with 5 g of thymol have been used. A description of these can be found at https://www.elgon.es under the heading “Gradual resistance”.

If the colony is untreated, the next step may be to check the hard board in front of the hive again within 10 days. The results of this check will help determine whether to 1) wait another 10 days at most to observe the hard board, 2) conclude that the colony is coping with the number of wing damaged bees, or 3) move the colony to a “hospital apiary,” perhaps at least 2 km away from other bees, and maybe treat it immediately to reduce the number of mites.

You may not see any bees with damaged wings on the Masonite board in front of the hive entrance at any point during the season. The colony has been treatment-free for several years. But the harvest is low. The colony is very strong at the start of winter. It overwinters very well. But development is weak the following spring and the harvest is very low. Without having to figure out the reason carefully, the conclusion is simple. Queen replacement is highly recommended. The reason may be different, including the fight against the number of mites, but no virus problems.

The new queens that are introduced into colonies where the queen is being replaced are bred from bee colonies in project apiaries where breeding work for varroa resistance is carried out, and they are mated in such an apiary. Bear in mind that it takes a long time before the new queen’s varroa hunter bees become numerous in the colony, perhaps until autumn, and then they start to clear the colony. At that point, you may see a significant natural decline in mites due to the new effective worker bees. The new queen cannot be fully assessed until the following year.

Counting mites METHOD 1

In the UK, many people used the natural mite fall method to count mites and decide which colonies to breed from and which queens to replace. Steve Riley describes in his book “The Honey Bee Solution to Varroa” how he went about this (see previous blog post: https://www.elgon.es/diary/?p=416888 ).

In 2019, a group had been selecting for varroa resistance for a couple of years. Riley had an apiary with five colonies, which he mentions in the book, page 84. 

For three months (March–May), he counted the daily mite fall for all 90 days and added up the totals. No mite control measures were taken during that period, nor during the late fall/winter before the period. For example, you can count the mite fall every five days using a mite tray. If the mite tray is left in place to collect mite fall for more than five days, a lot of wax debris may fall into it, making it difficult to distinguish and count the mites. 

The average daily average is not calculated, but rather all mites over the 5 days until approximately 3 x 30 days have been counted. The colonies that collected 500 mites or less qualified to continue in the project. If more than 500 had fallen during the period, such a colony may not qualify. One of the 5 was rejected. He moved it away from the apiary. 

From the 4 remaining, he bred queens and let them mate in the apiary. He used the resulting queens for splits and other bee colonies, such as the one he moved away. From the fifth colony, 2,200 mites fell during the 90-day period, and it was treated for varroa. It was moved so that its drones would not mate with the virgin queens. 

Drones from places other than the project apiary could potentially mate with the virgin queens. However, the location of this apiary was chosen to minimize that risk. If a few foreign drones did this, out of the approximately 20 that a queen mates with, it would not particularly affect the success of the work. After 5-6 years, it is possible to have a population of treatment-free/varroa-resistant bee colonies, as Riley achieved in this apiary.

This is a more labor-intensive method than METHOD 2. It works. Steve Riley and his colleagues have demonstrated this. 25% of all beekeepers in the UK are treatment-free.

Counting mites METHOD 2

With the second method, you count mites from 1 dl of bees (300 bees) 2 or 3 times a year to begin with, and eventually the goal is not at all. You do not need to count the bees. It is accurate enough for decision-making purposes to use a dl measure and not fill it below the 1 dl line. 

Shake the bees from a couple of frames without brood, but close to the brood in the brood chamber, into a plastic container. Or from the middle of the first honey super. Then you don’t need to find the queen and hang the frame with her aside. 

Shake the bees into a bottom corner of the plastic container and fill the deciliter measure. Pour the rest back into the colony after pouring 1 dl of bees into the shaking jar with 2 dl of technical alcohol. An EasyCheck jar will catch 100% of the mites if you spin the jar for ½ minute, wait quietly for ½ minute, lift the jar above your head, and look at the bottom. Then count the mites. The technical alcohol can be strained into the lid of the jar using a coffee strainer and poured back into the EasyCheck jar once it has been cleaned of any remaining mites and bees. Other types of shaker jars usually catch 90% of the mites. Powdered sugar and carbon dioxide used in a shake jar catch around 70%.

If more than 9 mites are counted in a colony sample, it is usually recommended to treat for mites within a week. If testing is carried out in mid-May, it may be appropriate to use 1 thymol pad made of dish cloth with 5 g of thymol. After 7-10 days, use a new thymol pad. Cover three weeks. See: https://www.elgon.es/gradualresistance.html

Any thymol treatment after testing later in the year will probably consist of 2 thymol pads every 7-10 days until approximately three weeks of treatment have been achieved. Will there be any thymol residue anywhere? Temporarily in the wax. You can smell it. Thymol works thanks to the smell of thymol. After a few weeks in the bee colony, it has been ventilated out of the wax frames.

If the May test shows 7-9 mites, a new test is performed 1 month later. In mid-August, the late summer test is performed. (In the Swedish climate.) The method is described here: https://www.elgon.es/varroalevel.html

Do you think it’s a shame that 300 bees have to die? Take into account in your decision that many bees die all the time, either from disease in individual bees to prevent disease in the entire colony, or when they work for the good of the colony in various ways. 

The queen lays at least 2,000 eggs per day for a long period during the season. Approximately 1,500 of these eggs hatch/are born. Approximately 1,000 are needed to replace the bees that die for various reasons each day during the high season – worn out wings, eaten by other insects and animals, etc. During the winter, bees die when they are “burned out” after keeping the rest of the colony warm. The bee colony expands by about 500 bees per day during the high season. 

If 300 bees serve in the shaking box 2-3 times during the season, the colony will be grateful for how much better it feels from a more effective varroa treatment or effective development towards increased resistance to both viruses and mites. After just over 5 years, it is possible to have developed a treatment-free/varroa-resistant population of bee colonies, especially if you can obtain queens or slits to start with from strains that show increased resistance.

Resistance traits

Bee colonies that are regularly treated for varroa without taking into account any resistance traits spread their genes with not particularly good resistance, which is not good for all bee colonies in the area of all beekeepers.

Bee colonies in an area dominated by such colonies increase their varroa mite populations over the course of the year, and virus amounts. The varroa mite population increases year after year until the colony with the most mites usually dies first, probably not from the mite population itself, but from the also increasing amount of viruses in the bees and mites. 

If breeding work is carried out using one of the methods for counting mites and varroa resistance is achieved in a population of bee colonies in an apiary and in a region, the varroa mite population in the colonies does not increase continuously. The varroa mite population fluctuates in waves in a colony, and starts again with approximately the same population in the spring, as last spring.

Steve Riley has discovered that after measuring the natural mite fall in a resistant colony, it starts with an average of 5 or fewer mites per day in the spring. It then varies up and down, but usually does not exceed 5. There may be a severe purge in late autumn/winter with about 25 mites in daily fall, then dropping to 5 before spring. During the ‘spike period’ period in late autumn/winter, there is no or only a little brood. The bees are not focused on raising brood or collecting nectar but are clearing mites, from each other and themselves, known as grooming.

During the brood rearing period, they primarily use various hygienic behaviors, including cleaning behaviors. They identify varroa mites in brood cells at the beginning of the pupal stage and their response are slightly different, which have been given slightly different names such as recapping, VSH, bald brood, and brood cell cleaning. The mites that survive such behaviours affects the infertility rate of the mite population in the colony. This is contributing to a trait of the bee colony called SMR. Hygienic activities occur to a lesser extent when other activities are ranked of more importance for the bee colony, such as collecting nectar, robbing other bees, or swarming. However, swarming, whether artificial or natural, also interrupts mite development and is important for the survival of bees and the creation of new bee colonies.

Conclusion

Count mites in some way, using method 1 or 2. Draw conclusions from the count in your work to increase varroa resistance in your apiary. As beekeepers in the UK have done (read more here about the work on varroa resistance that Stephen Martin and Steve Riley are involved in: https://www.varroaresistant.uk ), and many in Sweden and Norway. Collaborate with your neighbors.