Traits for Varroa resistance

We have found in our Varroa resistant project in our local bee club that when you begin a project like this, checking the varroa level is the most important tool, if you plan to treat colonies that have a varroa level above a threshold. Checking the varroa level is in the beginning of a project important not only once during the season, but about three times per season. The most reliable method we have found to be the alcohol wash method with a beeshaker. A good beeshaker is for example EasyCheck which you can buy from bee eqiupement dealers.

You may want to use the mobile app Beescanning. You can download it from Appstore or from Google Play. The app is often updated to make more and more accurat measuring. The app is also updated to contain more and more details for keeping track of your honeybee colonies, for example if a queen is spotted, or sick and disordered brood.

Varroa resistance is not relying on only one single trait with the bees, but many traits may bee involved. The two main traits (with more than one trait forming each one of these traits) is:

1. The ability to keep the Varroa population low during the season, with some temporarily higher values.

2. The ability to keep the virus populations low during the season, with some temporarily higher values.

The colony will not be seriously affected by viruses, even if the Varroa population and the virus populations will raise during short periods due to different reasons, for example reinvasion of Varroa mites, though not of a large scale.

A key word here is microbiome: the composition of different kinds of microbes, for example bacteria, fungi and viruses. They keep one another in balance and form a strong force to help the creature. The microbiome is existing in and on the creature. This microbiome ”family” is also a part of the creatures defense/immune system. Disrupt this balance (which can be done with chemicals) and one part of it can get the chance to grow too much. The viruses may be increasing too much due to killing of bacteria.

The key is to create a better environment for the microbiome so it can regain a better composition, with less of viruses. Thus this better mixture of the microbes will help getting the viruses in a better (lower) amount in the microbiome. We have tried to do this through selecting the colonies with the lowest Varroa levels to breed from.

If possible do not treat the first year of a new queen in a colony. Measure the Varroa level when the first real flow begins in spring the year after the treatment free year. Those colonies with lowest Varroa level in spring that year are used to breed from.

Most important replace the 30 % least good queens every year. Let many colonies superseed their queens if possible to keep a good genetic variation in the stock. And make walk away-splits (they are allowed to raise their own queen) from good colonies (which are not used to breed from), to keep a good genetic variation in your stock.

When the bees are enough good to keep the Varroa population down, it will be possible to measure the varroa level fewer times during the season. But drop the spring measurement at the latest, if ever.

Checking virus susceptibility is made through watching how much of crippled winged bees appear on the hard board (0.5 x 0.5 meter) in front of the entrance. Look at how to do this checking.

With the help of the hard board you check the presence of crippled winged bees, the sign of the virus DWV. This is the most common virus in connection with Varroa mites. In the beginning of a Varroa resistance project you have to treat a colony showing maybe only one DWV-bee, if you don’t want to risk to lose it. When the resistance is high you may see even several, at the end of the season, several weeks after each other. The colony can still winter in a healthy and strong shape. The picture is taken in the middle of August when it’s time here to feed supplementary sugar solution for winter feed, if that is needed. Many colonies this year were wintered with four square shallow boxes like this colony, with the top box almost full of honey. And they fill the boxes with bees and are prepared for an early flow next year.

The Varroa treatment chemical that we think is best suited to decrease when possible is thymol. It seems that if only a peace of dishcloth with just 5 grams of thymol is used in a year (in late summer) this amount will not interfere too much with the microbiome.

Also it will probably be possible to stop treating altogether with the best colonies. Especially if the number of colonies in the apiary is low (2-4) and the distance to other apiaries is about 1 mile (1-2 km). When you have reached this far in your project you are probably experienced enough to start skipping treating of the best and of good enough colonies.

In some years you will be able to stop treating altogether and losing only acceptable number of colonies annually. Can you guess how many of my 90 colonies I treated this season?

Varroa resistance – the two traits
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2 thoughts on “Varroa resistance – the two traits

  • October 14, 2021 at 14:17

    Another excellent article. Here in USA, folks use mostly acid vaporization for mite control, which is NOT natural in any way. They are also forced to re-queen colonies every year. Yet naturally untreated colonies follow a yearly pattern of swarming and re-queening and do not require such harsh treatments. I wonder if the disruption in the microbiome from this acid vapor bath is in fact a major disruption that is being overlooked by so many. Our loss rates in this country are every increasing in the operations using conventional mite control methods and feeding artificial diets. I suggest we see a 100% turn over in colonies every year. Seems the more we tinker with honeybees, the more problems the bees face?

  • October 14, 2021 at 21:23

    @Bill: I think you spoke about formic acid vaporization. I believe vaporization/sublimation of oxalic acid is rather mild for the bees – does anyone know something about the effect of this method on the bees microbiom?


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