Spring 2022 – Review 2021


As in the first Corona year, also in 2021, the participating beekeepers have been able to actively work in the program with spectacularly good results. We now see that the enormous amount of work done since 2014 proves that the assumptions we started with – that there is a little bit of Varroa Sensitive Hygiene (VSH) in the honeybee population and that that can be selected for by Single Drone Insemination (based on the work from the USDA going back to 1997) – are working out in practice.  

In this introduction we first give you a “refresher” on the method we are using, followed by the latest results.

The method is based on 4 types of mating of the queens; Single Drone Insemination, Multi Drone Insemination, Land mating stations and Island mating stations. Each of these types of mating has its own advantages (and disadvantages), but are powerful if used for the right purpose. That is why the overall program is a mix of these 4 types.

  1. Single Drone Insemination (SDI):
Artificial insemination at Beers, NL.

This is the first and important step of the selection of Varroa Sensitive Hygiene (VSH). We produce large numbers of small colonies with different genetic backgrounds. Each colony is headed by a queen inseminated with a single drone.

After adding extra Varroa mites, we investigate the brood and determine the level of resistance (Varroa Sensitive Hygiene, VSH). This allows us to basically find those queens/colonies that were mated with a highly resistant drone. Only colonies with queens that remove 75% or more of the mites are kept. The daughters of these queens will carry the resistance genes, creating the basis of the breeding program.

Please note that at the beginning of this selection process we estimated that only 10% of the drones would carry enough VSH genes.

In the case you use more than one drone at this stage, like in normal mating with approximately 10 drones, the effect of one drone carrying enough VSH genes is diluted by the 9 other drones carrying no or little VSH gens. When VSH genes are diluted, there is not enough resistance left to detect/measure it.

2. Multi Drone Insemination (MDI):

Multi Drone Insemination (MDI) at Beers, NL

The SDI colonies are very well suited starting from a population with limited VSH genes. SDI colonies can only be small and are relatively short lived (because of the limited amount of sperm stored by the queen). As they are small, the colonies cannot be easily selected for the other important traits as honey production and low tendency to swarm. For this reason, we inseminate a larger number of queens with the semen of at least 10 drones. As we are now later in the selection process, most of the drones will carry the resistant genes. These colonies can be kept much longer (2 to 4 years) and can be tested for the described traits. We also monitor the varroa population growth in these colonies by taking samples (300 bees per colony) to determine the number of mites on these bees (instead of in the brood), called the “phoretic” mite count. This is a method that can be used at large number of colonies without too much labor involved.

The advantage of using Multi Drone Inseminations is that we can keep the biodiversity as high as possible. We can use a large variety of different drone lines compared to a mating station that usually has only one or two different lines per year.

3. Land Mating station:

The disadvantage of the MDI colonies is that it requires special insemination skills. The amount of work involved makes it less suitable to do large scale production of mated queens in the broader beekeeper community. Therefor we are more and more making use of land mating stations. On such a mating station, ideally somewhat isolated from other apiaries, we place colonies that will deliver drones carrying varroa resistance genes. As this is a land mating station, we assume that a certain, hopefully low, percentage of the drones comes from colonies from other beekeepers. This means that the mated queens will not produce 100% “pure” colonies. However, the queens mated on these stations can be used in production colonies in which they will be assessed for our selection program.

So from these land mated station queens/colonies we do not produce further queen offspring (they could have low resistant genes from the not-pure drones), but we can definitely use the (pure!) drones for our selection program.

Indeed, the best colonies can then deliver well selected drones, because drones are coming from unfertilized eggs. They just represent the genes of their mother, they have no direct biological father!

We have experienced in our Hawaii program and now also in our EU program that using this step is actually very powerful. Given the relatively large number of colonies that can be produced and monitored (only a few samples of bee washing are needed for phoretic mite level assessments per year), a both strong and still broad selection can be made based on high resistance as well as good honey collectors, gentleness and with low swarming tendency.

4. Isolated mating station:

Whereas the previous methods are very helpful during the selection process, they are not very useful for diffusing the breeding progress to the beekeepers that do not participate in the selection program. Those beekeepers are interested in purely mated queens (“F0”) that  can be used to graft from in order to produce their own F1 queens for their production colonies. For this distribution of good traits, using an isolated mating station (an island or a remote mountain valley) can be a very efficient way. We will see that more and more isolated mating stations are using Arista or (at least partially) Arista derived queens as the basis for their drone lines. This will facilitate the distribution of the resistant genes in the different honeybee  populations – and will eventually even benefit beekeepers that are not visiting mating stations at all as their queens will be more often mated with varroa resistant drones from their neighbors.

It is important to note that we are not yet in a position to supply all these mating stations with new, non-related and highly resistant queens, year after year. We should also ensure that we do not lose the more than 100 years of selection (either by beekeepers or by nature) by moving too fast with the still limited number of Arista validated lines. We are now at the turning  point; we need the full support of the beekeeping community but also from the governments to extend the program and to ensure that we keep the genetic base of the honeybee as broad as possible. The method works, it is “just” a matter of implementing it 😊…

Progress in the breeding program


Dr. Guillaume Misslin, our Project Leader located in the Netherlands and Sacha d’Hoop, our Project Leader located in Belgium, support around 200 beekeepers distributed in 18 groups within: Belgium, Germany, France, Luxembourg, the Netherlands, Austria and Switzerland. In the 18 groups all three main races of bees are represented: Black, Carnica and Buckfast bees.

SDI-Varroa counting sessions at Paul Jungels, LUX.

In Belgium we could welcome a new Project Leader: Julien Duwez. Freshly graduated in bioengineering from Gembloux, he was already involved in the project as a participant before starting to work with us. His arrival in the team will allow us to improve the coordination and the follow-up of the participating Wallonia beekeepers as well as to improve the training of those that recently joined us.

Explanation of the method at Sélange, BE.

The beekeepers in the program are supported by the Project Leaders in the choices to be made in the use of lines, in the queen and drone breeding techniques and in the varroa infestation and counting sessions. Furthermore, the Project Leaders also organize insemination courses with the groups, so they gain more autonomy and flexibility.

The total number of colonies that has to be followed and monitored is increasing as we now maintain more and more colonies mated in the different described ways. For this we fortunately have our in-house, tailormade web-based database application “Queenbase”. It is more than ever the tool to be used; to report back to the Project Leaders the production and phoretic data of the colonies gathered during each season as well as the pedigrees and offspring data for the queens in these colonies.

Single Drone Insemination results

The number of colonies we could test for removal behavior (Varroa Sensitive Hygiene; VSH) in SDI colonies was 969, an increase of 56 compared to the previous year. As in previous years, about 1/3 of the colonies removed more than 75% of the reproductive mites (the minimum required to not need chemical treatment). These high VSH colonies can be used in the breeding program.

Varroa family in a brood cell

More than 100 of the high-VSH colonies removed all – 100% – of the reproductive mites from the worker brood. We have now demonstrated this year after year, but it is still a small wonder to see that the bees remove the Varroa mites so well themselves and that this trait is transferred into the next generation. To evaluate the colonies, volunteers open the brood cells to investigate its content. The total amount of opened brood cells is still increasing compared to previous years as at higher VSH levels we find less mites, so we open more cells to still get enough information. Furthermore, we do more and more recounts, just to be sure that the high scores are indeed sustainable if measured multiple times.

The fact that 2/3 of the hives are not high VSH is because we ask the beekeepers to keep bringing in new blood (good, new lines, but not VSH). Therefore, the program is a mix of new lines that are in the first years of selection (initially low VSH) and already proven lines (high VSH).

Land mating stations and Multi Drone Insemination results


As we described in the “Land mating” paragraph, and as we learned in our Hawaii program, you can make a very good contribution in the selection by using production colonies.

Collecting drones in Italy.

As also described in previous updates, we have been able to build a “well-oiled machine” with a group of highly skilled professional beekeepers in Italy. Every spring, and thus also in 2021, we delivered a set of SDI colonies to this group. From these, more than 300 queens are bred and mated with drones from colonies also coming from our program (selection from the previous year). These 300+ queens are heading production colonies that have to prove themselves in production and are followed and evaluated for several years on the phoretic mite infestation (simple sample of bees “washed”), gentleness, honey yield and low inclination to swarm. From the best colonies (after 1, 2 or 3 years) large amounts of semen are collected by capable inseminators/beekeepers during a second visit in the spring. This semen is transported in proper conditions and used for multiple-drone inseminations of breeder queens at the beekeepers from the different participating countries.

2021 is a special year for this selection. After all the years of preparation and pre-selection, this was the year that queens, inseminated in 2020, had to prove themselves (for more than) a full year. For this purpose, in 2021, 16 queens in the Netherlands were followed by taking samples. Throughout the full year these colonies, of course without any treatment, kept the mite infestation around half a percent! Control colonies (non-VSH) would have grown the mite levels to around 10% in the same timeframe.  We are very happy and proud of these excellent results – made possible by 8 years of work with a good cooperating group of now 200 beekeepers.

It is furthermore striking that already in spring these colonies seem much larger and healthier than “before” (in the early 1980’s, the Varroa mite entered our countries). And also in the fall the colonies are large and look more healthy compared to what we are used to.

Maybe this should not be a surprise? The bees are doing something that beekeepers cannot do that is removing Varroa mites 24 hours a day, 7 days a week. As a result, the pathogenic virus infections (distributed by the mites) never have a chance. This is the main difference with the current practice of chemical treatment. You can treat as good as you can as a beekeeper (e.g. 3 times a year), but the virus infections only decrease slowly after a Varroa treatment (takes weeks/months). In fact, you don’t directly treat against the viruses that are causing the main problem for the colonies. And after a chemical treatment against the Varroa, it just starts growing again, until the next treatment. The still present viruses can then just “hitchhike” again. And last but not least, there is no impact of chemical treatments on the bees. Now that we can actually start beekeeping with really healthy colonies again, we realize more and more to what we have become “accustomed” to in the past 40 years… it is truly a relief to be able to practice beekeeping with “normal”, healthy colonies again!


The method used with our Italian colleagues, is also implemented in Belgium and the Netherlands.

In Belgium we established the first transnational resistant mating station in Sélange (type “land mating station”). It is the result of a partnership with l’Abeille Arlonaise, a beekeeping section from the south of Belgium. Not only is the aim to allow high resistance matings, but also to create an area without varroa treatment on the long term. In 2021, the mating station was opened to members, generating around 360 queens from many different resistant lines, that can be used to produce males for future inseminated queens. It is asked not to treat any of the colonies that originate from those queens, unless a phoretic count proves it is necessary (which obviously eliminates these queens from the program).

Text Box: Arista land mating station at Sélange, BE.
Arista land mating station at Sélange, BE.


Arista land mating station at Bronlaak, NL.

Also in the Netherlands we opened our own land mating station, close to our offices. This station is run by local beekeepers and coordinated by Arista. We have admitted 14 beekeepers for the time being. These beekeepers receive the starting material (larvae) for queen breeding from us and then have these virgin queens mated in small fertilization boxes. Just like in Italy, the fertilized queens can then be used in production colonies for the further selection of good drone material in the coming years.

Island mating stations

The VSH lines that become available have also drawn the interest of several island mating stations. They are reserving part of their capacity for putting lines on their mating station that have certain levels of VSH incorporated.  

Ameland (the Netherlands) has had several different VSH lines at the station in 2021 on a separate part of their island. This enabled Arista beekeepers to send their mating colonies and select for different lines.

Also in Germany there are more and more mating stations that can now include Varroa resistance as a selection criterion by using queens that have an origin in the Arista breeding program.

In 2021 a first start was made on a cooperation program with the Flevoland group/station. This group will from now on be solely dedicated with the selection and distribution of Varroa resistant queens. Already in 2023 the mating station will be “manned” with queens coming out of the Arista breeding program.

As earlier stated, we are too early in the program to fully switch to varroa resistant queens on all the mating stations. For that we need a more diverse and broader selection of resistant lines – respecting the large amount of work and quality available in the not-yet varroa resistant lines.


Genetic marker for VSH

In the Genetic marker project we are trying to find the genes – or a genetic marker for these genes – that are linked to the VSH behavior (collaboration Arista, Van Hall Larenstein, Inholland, Bejo Zaden). We are very close to a first, very important analysis as full genome of the target colonies has been sequenced. If all goes well the first analysis on the full set of data will be available this summer (2022). Hopefully we will have a first indication whether we will indeed have a powerful tool to speed up the selection… to be continued!

VSH rapid test

It is important that we find ways to make the very labor-intensive selection more efficient and/or effective which is a reason for the described genetic marker research. The selection process could be more efficient if we would have a way to select for the VSH trait without having to breed, infest and count the Varroa mites themselves…

We are therefore pleased that the Goeie Grutten Foundation has granted us a subsidy (starting in 2022) to develop a VSH rapid test. Such a test would not require Varroa mites and would have to give a relatively quick idea of the level of Varroa resistance/VSH. For this, we will look at specific odorants that might be used in place of the mite. For this part of the research we work together with the University of Greensboro (US), the Buckfast Flanders group and the University of Leuven.

We will also investigate other ways to mimic the effects of the Varroa, without using the Varroa mites themselves.

Arista hives

Arista sponsor hive

At the end of 2021, we had a total of 21 installed Arista sponsor hives. These hives have queens from our selection program and are used to further evaluate and use the best lines. Both in 2021 and 2022 we already distributed drone brood and larvae from the best of these colonies to mating stations and participating Arista beekeepers.

A nice “side-effect” is that those (regional) beekeepers that take care of the hives often are new to our program. Their first-hand experience and their own network make our program known to a wider group of beekeepers.

Furthermore, we have spent a lot of time, with also highly skilled “pensionados”, on the proper functioning of the monitor system (weight/temperature/beecount in-out). The current version is very stable, works in all places where we have hives and is fully integrated with the software (Queenbase) of our breeding program.

The financial contribution from these hives is critical to the survival of our breeding operation. We hope we can further expand this program and welcome more donors/sponsors for an Arista hive!

Thank you

We thank our donors and sponsors for their financial contributions that enable us the organizing of this complex pan-European program.

We thank all the participating beekeepers and volunteers for the incredible amount of time, passion and expertise they invest in the Varroa Resistance breeding program on a daily basis.