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My first 12 years with Varroa
I started long before the mite arrived to focus on increasing the varroa resistance in my stock. 1989 I went to the mountains of Kenya to get genetic material that were more related to the resistant bees in South America than we had in Europe. You can read somewhat more about this on the following two links:
Maybe I had reached the results I have achieved today without going to a couple of mountains in Kenya. It wasn't easy to go there and it hasn't been without constant work to make a new combination breed. But here I am with what I call Elgon bees. I don't want any other bees today.

I have tried a new breed for eventual combination now and then. Now maybe one such combination may be included as a mother line. Those earlier tried couldn't compete well enough to stay as a mother line, but they have probably contributed somewhat on the drone side.

In the beginning of the combination work I focused on securing the theoretical Monticola heritage. After the mite arrived to my area focus has been on varroa resistance regardless of any special heritage. Still today I recognize several African traits: flying characteristics, color of thorax, reactions when opening a hive, flying at low temperatures, development time of the brood and queen, stronger queen pheromon affecting field bees in some different ways in splits and nucs.

Varroa was seen in my hives 2007.
Two pure Monticola worker bees with a buckfast worker bee in the middle in a small Apidea mating nuc in May 1989.
A deep brood frame 366 mm wide from a F1 Monticola queen mated to Buckfast drones in July 1989
Treatment free Elgon beekeepers
When the mites finally reached my apiaries there were beekeepers with Elgons in Denmark (Poul-Erik Karlsen), Finland (Sven-Olof Ohlsson), Norway (Hans-Otto Johnsen) and southern part of Sweden (Leif Hjalmarsson, one apiary) and finally just 100 km from me (Thore Härnkloo) who hadn't used any treatments at all for more than 10 years (including drone brood removal. The bees did it all by themselves, fought the mites.

These beekeepers had one thing in common. Their bees were quite isolated from other bees. Four of them were on small cell (two of these on 5.1 mm cell size, one on 5.1 and 4.9 and one on 4.9). One was on large cells, 5.4 mm
My preparations
I also took my bees down on small cell, 4.9 mm. I did everything I could to prepare for the arrival of the mite. I guess I hoped it was enough to escape the need for treatments without having any losses but a few due to the mite. I was wrong.

I didn't want to use pesticides like Apistan as residues of it builds up in wax and propolis. And I didn't want to use acids because of the risks for myself, as well as for the bees. So I was left with thymol to use, if I thought the bees needed it.
Why the varroa hit hard in the beginning
Why was my bees affected severely by the mites initially? There were quite a few Elgon beekeepers that didn't use treatments.

One part of the answer is the relative isolation of these beekeepers. In my circumstances there was a constant reinvasion of mites. The amount of virus in mites was bigger then than it had been when varroa had come to southern Sweden. It appeared there in 1991 and was found 2007 at my place. So viruses had had at least 15 years to build up in mites conquering the north. The ability to start a disease for viruses is a dose question as well as the quality of the immune system.

In addition the distance between my apiaries are sometimes small. And the number of colonies in each apiary were in average much higher than today.
Now when the resistance is much better in the Elgons and the microbiome has gained strength (and then the immune system) I see a much better situation also in apiaries with higher numbers of colonies.
I write about how I use Thymol here:
Better varroa resistance
The strategy of using thymol when virus problems occurred made my stock more resistant. But I realized that it also caused an ongoing reinvasion of mites keeping the mite pressure higher than wanted in the apiaries. The use of chemicals help viruses to reproduce better, both in bees and mites. So today you need smaller populations of mites to get virus problems (if you treat regularly and preventive). My bees had become more resistant also to viruses but the virus level was kept high and made it difficult for a continuation of the improvement in resistance.
New strategies
I decided to change my strategy and try somewhat new strategies after considering the points listed below. I have tried out these points in the strategies described below during some years now. One point that is not mentioned but that is always present is to disturb the bee colonies as little as possible. The most important points come first.
The most important part of a resistance project is to measure the varroa level when you eliminate treatment step by step
When the varroa level exceeds the threshold of 3% varroa level it's time for thymol pads within a week.
• Measuring the varroa level
I didn't like the ongoing reinfestation of colonies in my apiaries. It contributed a lot to the difficulties my bees were having to get a varroa resistance at an effective level. My thoughts went to the beeshaker Michael Palmer gave me some years ago. (Thanks Mike!) I did not understand fully then how it would contribute to the work of achieving varroa resistance. One day I read on Randy Oliver's website and found the beeshaker there and how to use it. I also talked with Randy when he visited Sweden some years thereafter. I realized it could benefit a lot.
You can read more about the beeshaker here:
Eric Ericson had the threshold 15% varroa level when a colony was dismissed from his varroa resistance breeding program that started in 1995.
When the program had went on for a couple of years he lowered his threshold to 10%.

A few years ago recommendations to treat when varroa level was above 5% were common. Today you can see recommendations of immediate treatment when Varroa level is above 3%. Today mites and bees have been more filled with viruses and they will quicker develop problems. This makes it more difficult to get treatment free.

After talking with Randy Oliver and considering my own experiences I understand an appropriate varroa level threshold is 3% regardless of the time of the season. A shaker test is made at least twice during the season, in early May (spring) and in early August (late summer). In areas where there are longer seasons then where I live in Sweden, three and maybe four times monitoring is probably a good idea, at least in the beginning of a resistance project.

If the spring test gives a value just below 3% a new test is scheduled a month later with that colony.
By monitoring the varroa level I will get a good idea of the resistance value of my colonies without creating a lot of reinvasion problems. But still my bees can pick up mites from other beekeepers' bees of course.

If I have my bees relatively isolated I will give them a good chance to develop their resistance traits without getting a lot of mites from other bees. The inferior colonies will get new queens as soon as possible. The very worst colonies it's good to move to apiaries furthest away from the center of the resistance project.
• Distance of 2-3 km (1.5-2 miles) to other bees
Especially in the difficult year of 2015 I thought about the experiences of a number of beekeepers with Elgon bees, beekeepers that hadn't been treating against Varroa for 10 or more years, with small problems from the mite. They had in common that they were isolated from other bees or/and dominated their area heavily with their bees.
Poul Erik Karlsen on the island Bornholm in the Baltic. He used 5.1 mm cell size. He is now retired and after many years being a relatively big beekeeper on the island.
Sven-Olof Ohlsson in western Finland with around 200 colonies. He used mainly 5.1 mm cell size, but also some 4.9. He is now retired but his son is continuing with the bees.
Hans-Otto Johnsen in eastern Norway with several hundred of colonies. He hasn't been treating for more than 15 years. He uses 4.9 cell size. He also makes his own wax foundation with a commercially quality set up. Officials have found the varroa level is very low in his bees. He made a good small cell test.
The friend of Hans-Otto, Terje Reinhertsen has in principal never treated for varroa mites:
Leif Hjalmarsson in the southern part of Sweden. He used 5.4 mm cell size. Another difference with him and the others was that his Elgon bees didn't have any problems with the mite from the start. The mite had arrived in his operation some 5 years before he received 5 queens from me. He had all the time treated all his bees with Apistan, an effective miticide.
Leif started his Elgon colonies with very low levels of mites. After introduction of the queens in their colonies he moved them to an isolated spot in the forest more than 3 km from other bees. He didn't treat his Elgons for about 15 years. He got some new queens from me when he needed. But many colonies just shifted their queens themselves. Unfortunately he grew old as we all do and got a stroke. He passed away early in 2016. He was a good friend and a good beekeeper.
Leif Hjalmarsson at his 3 km isolated apiary with Elgon colonies since established in 1998. Here he kept 5-7 colonies without treatment until he died in 2016.
• Few colonies in apiaries
I designed my apiaries with fewer than previously used number of colonies, sometimes only one.

In those with only one colony I had moved colonies that had needed some treatment, but not full dose. The following years they didn't need any treatment any more. It was 2 km (1,5 mile) to other apiaries. The distance that bees normally fly in whatever activities they are involved in, for example so called quiet robbing is mostly that distance.

The experiences from the above tested points give good advice for designing good circumstances for developing a resistant bee stock.
• Move the most inferior colonies away
Inspired by Eric Erickson,
the most inferior colonies concerning resistance (as well as bad temper, low crop, development, etc) were moved to a couple of apiaries furthest away from my other colonies. This took place first time just receently, but had a tremendous effect on lowering the average varroa level in the colonies. In the season 2020 only 20% of the colonies were treated (about 45% the year before). Most of the treated ones only got ¼ – ½ of a full thymol treatment, which now is 20 gram [2x5gr (x2)] not 30-40 gram as it was 10 years ago.

These far away apiaries are situated in a forested area with only those colonies. Four colonies in one, and three colonies in the second. Surprisingly these colonies that had been treated full doses the year before, now developed only low varroa levels. I had expected that I would loose some of them, but I didn't. Half of them were treated with 5-10 gr thymol (thymol pads). The other half nothing.
• Make splits from the best
After seeing that colonies that I had to treat with a full dose of thymol, and requeened them next year with a grafted queencell, they still often had to be treated effectively as virus effects were seen. This could go on for several queen replacements with grafted queens (and superseded ones).
So I decided to make splits if possible only from colonies that had not been treated for varroa, or treated very little. Such splits many times were allowed to produce their own queen. They were seldom needing any treatment.

The conclusion is that chemical (organic and other) treatments make the bees more susceptible for pathogens, such as viruses. In this case especially Deformed Wing Virus (DWV). And that it takes time for the microbiome to come back into harmony. The new queen has to get a very good set up of resistance traits in her worker bees to overcome the difficulties of the microbiome getting back to normal.
• VSH (Varroa Sensitive Hygien)
A good way to control the degree of VSH. Pull out pupae with tweezers and look for mites, mite feces and mite offspring. When the bees have a high VSH value the varroa population will be so low that it will be difficult to find enough many invaded brood cells and varroa mites. It may involve so much work that it will too difficult for practical purposes. Probably monitoring the varroa level is enough when resistance is high in a bee population.
In spring 2013 I listened to John Harbo and started to check my most promising colonies that year:
In 2014 I measured the most promising colonies again for their VSH value. I found one with VSH 80% and of course bred from it. I got very good feedback concerning daughters from this colony from other beekeepers in 2015. But daughters in my operation were among the first to show deformed winged bees (DWV – Deformed Wing Virus). Maybe a very intense selection on hight VSH might come along with some unwanted trait, as higher susceptibility for viruses? There are more traits to help fight the mites than VSH. Maybe VSH 50% is enough in a good resistance mix of traits.
• Us of feral colonies
In many places where a population of honey bee colonies has developed resistance to the Varroa mite, feral colonies are a part of the success. They contribute apparently. Their adaptation is not disturbed by miticide chemicals, and many times not but agro chemicals either.

I have caught a couple of swarms from feral colonies. They both showed a VSH value of 50%. Both showed evident monticola/elgon traits. The second swarm less, and it came from an outher edge of the Elgon area. The first came from nearby to the center of the Elgon area. The first swarm have been the start of a good mother line in the Elgon stock. There's only only one struggling colony left of the mother line from the second swarm.

The conclusion is that you can't be sure feral swarms will add good genetics to your stock. They may be. You have to check them as thorough as you do with all your colonies keep the superior and cull the inferior.
• Not moving bees around
One big stress factor for bees are moving them to new places. It enhances drifting and mixing of bees and mites. Harmony takes time to get back, time during which defense systems woun't function to 100%.

I also glanced at how Dee and Ed Lusby worked when Varroa hit their operation in the Sonoran desert in Arizona. They lost 90 % of their hives due to the Varroa mite when it hit their bees. In some apiaries the number of colonies went down to just one single colony. Lusby's though didn't collect them together in apiaries, but let them keep their place and built up the number again apiary by apiary. Also catching swarms.
In nature feral colonies are stationary, or swarm. And there are never many colonies in an "apiary". Feral "apiaries" are most often not very close situated.

I reasoned it wouldn't hurt to try stopping move splits between apiaries, instead keeping the splits in the same apiary.
Today I can say that moving a split from one apiary to another doesn't give noticeable negative effects. On the contrary it has benefits, for example keeping the field bees in the split.
• Starting with almost zero mites
I thought a lot about Leif Hjalmarsson's experiences. He had kept a low mite level in his colonies all the time with synthetic chemicals before he started his resistance apiary 3 km from other bees. I concluded that I had to try to make a relatively isolated apiary as mite-free as possible with an effective chemical and see what happened. I did not like to do this, but I could not dismiss this option to learn more about achieving varroa resistance.

I did so and it looked good the first year, but after a couple of years the situation was no different in that apiary compared to my others. The most important thing is to measure the mite level regularly.
Resulting strategy
These points tried in different strategies, together with experiences during all the years with varroa has formed the strategy below. Most important first. The described strategy is fitted to the beginning of a resistance project. The are more articles on this website describing breeding varroa resistant bees.
• Measure the varroa level
Probably three times a year, during the time when normal amount of brood is present. Most important is the spring measurement. The threshold for treating is 3%. If varroa level is 2-3%, measure again within 4 weeks.

• Complementary observations
Observe THE PRECENSE of eventual crippled winged bees (DWV) and parts of bee pupae on a 0.5 x 0.5 m hard board in front of the entrance. Every 7-10 days. One or two DWV-bees montitor varroa level. Three or more consider threating without montitoring.
Observe THE DEVELOPMENT of the colony. Is it as expected or not. Maybe time to check the brood frames for eventual disorders.
Observe the appearance of areas with CAPPED BROOD during main brood season. Do you find dense capped areas or a "shotgun" pattern where uniform capped appearances are expected.

• Preferably keep a distance of 2-3 km (1.5-2 miles) to other bees.

• Keep as few colonies in an apiary as is pratical possible.

• Use normal small cells at least in the central part of the broodnest.

• Move the most inferior colonies away to an apiary furthest possible distance away from the center of the resistance project area.

• Make splits from the most resistant colonies. Preferably move a split if without the queen 2-3 km to another apiary.

• Replace queens in the inferior 30% of the colonies, with queens from your superior colonies, in the form of queen pupae or laying queens mated in the best resistant area.

• When it's time to establish another apiary, make it if possible 1-2 km from the center of the most resistant bees.

• VSH (Varroa Sensitive Hygien), bald brood and recapping behaviour. Make a positive note of such observations in your colonies, but a low varroa level is more important.

• Try feral bees if you get the opportunity. They have to bee laid under the same strategy scheme as the other bees.