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Varroa Management

Varroa Management

Posted by Bruce Clow on 25th Jan 2022

Varroa Management

I had the pleasure of attending the American Beekeepers’ Federation conference this January 2015, and one of the sessions was on varroa management.

Usually when we think of dealing with varroa, we immediately think of ‘strips’ of something. Well there is much more that can be done, and perhaps should be done before we hit the problem with ‘strips’. Understanding the life cycle of the varroa mite is critical in managing the parasite. Essentially, the varroa mite to expand in numbers needs brood. The eggs of the mite are laid in the brood cells and the young mites feed on the bee larvae and pupae, emerging as adults with the young bee. Adult varroa mites winter over when there is no brood by attaching to and sucking nourishment out of adult bees until the queen again starts to lay. As the brood increases, the varroa mite levels follow inevitably if we don’t intervene.

For hobby beekeepers there are a number of hive management techniques that can have a significant benefit. Unfortunately for the commercial beekeeper some of the more labour intensive methods just aren’t practical, and they must rely on ‘strips’ or similar to deal to the varroa. In any case here are some basic management practices that can help reduce the mite load in your hives.

The first thing that is critical is to monitor your mite levels. There are a number methods to do this, but we have developed an easy and effective tool for everyone to accurately determine the level of infestation in their hives. This is the VarroaMite Test Bottle. It uses the 'alcohol wash' method to more effectively collect the varroa that is present in the sample. This test bottle includes a filter trap, measuring cup and detailed instructions on how to conduct the test. If you want to do a sugar shake test, you can also do this using this bottle, but the results may not be as accurate. 

The last link there is from Country Rube. She is a dedicated organic beekeeper and has lots of good suggestions. In dealing with varroa, her first comment is that the best management tool is a screened bottom board, and I must agree. Why give a mite that falls off a bee the opportunity to grab onto another bee that is passing by. Use the natural mite fall to get the mites out of the hive. Some people are concerned that the bees will be too cold in the winter, but I find that they cope well. I will winter over with two brood boxes and the cluster will simply move up into the second brood box if they are too cold in the bottom.

If you have more than one hive, good practice for varroa control is to keep them far away from each other, and other people’s hives. Once you have the mite level under control it can be frustrating if with bee drift, bees from other hives carrying mites re-infest your clean hive. Unfortunately it is not always practical due to space constraints.

In that last link, Country Rube uses powdered sugar to not only measure mite levels but to also cleanse the hive of varroa. It looks like a good method, but time consuming, so won’t suit every one.

Another non-chemical technique is to use a sacrificial drone frame. Because drone comb is larger than worker brood comb, and the drone gestation is longer, varroa will preferentially lay in drone comb. By using a frame of drone foundation or a plastic drone frame, once the frame has been filled with capped drone brood, remove the frame and freeze it for a few days. This will kill any varroa eggs and young that had been laid in it. Then once it has thawed out completely, put it back in the hive. The bees will clean out the dead drone brood and mite young. Then the queen will again fill it with drone brood to repeat the cycle. It has been shown that this technique will reduce the mite load in hives by up to 20%. Of course this will only work when the queen is laying, so is only effective in the spring build-up and over the summer. There is a cost of course. If the queen is busy laying drone eggs, she won’t at the same time be laying fertilised worker eggs. The spring build up will not be as dramatic, and could affect the size of a honey crop. Also, initially, the workers will have to draw the comb and it takes hive resources to do this. Nothing comes for free.

We stock and sell the Pierco (USA) drone frame, the original designer and manufacturer of plastic drone comb frames. Most people don’t know that we also manufacture drone comb beeswax foundation. This would be ideal for use as a sacrificial drone comb, as I have always found that bees draw beeswax foundation in wood frames before they draw plastic frames. And since you won’t be putting these frames in an extractor they should have a good long reusable life.

Another method of varroa control is using food grade mineral oil fogging. This link shows you how to do this.

Very popular is the use of organic acids, primarily oxalic acid and formic acid. Because they have not been registered for use in New Zealand, as a supplier of beekeeping supplies I am not allowed to tell you how to use them, so you will have to search for websites to find out more. You are able to use them for your own hives.

Another natural method is to use thymol. Thymol is an extract from thyme and is actually used in several things that you already consume, like some fizzy drinks and toothpastes. In any case in a concentrated form it is very effective in mite control, the key being the temperature when it is used and making sure the bees can easily get at the material. If you can get thymol crystals you can use them, but we sell thymol in a tray of a pre-measured gel, or tubs with measuring scoops. It is produced by Vita-Europe and sold under the brand name, Apiguard. Apiguard has been shown to kill up to 97% of all mites in a hive, so it can be very effective when used under the right conditions. Check out the link to learn more.

Now we come to the chemical treatments that have as their two main advantages, a very effective high kill rate, and ease of use. The obvious disadvantages are they introduce a chemical to the hive, and inevitably there will be residues in either the honey or wax or other bee products, depending on the particular chemical and its properties. Governments publish acceptable limits for these chemicals in foodstuffs, which are considered safe, but many if not most people would prefer there weren’t any residues at all. Another issue is that each chemical usually has a particular method for killing the target species, in this case the varroa mite, and over time the mite population can develop a level of resistance to the chemical. It is essential that the directions for the use of each treatment are followed scrupulously to prevent very quick resistance development. The only sure way to prevent the development of resistance is to rotate treatments between chemical classes or with effective non-chemical methods of treatment, such as Apiguard.

The most common chemical class used are synthetic pyrethroids (similar chemical to pyrethrum in derris dust). These are very effective resulting in up to a 100% kill rate in non-resistant mite populations. They are lethal to mites at concentrations many times lower than the lethal dose for a bee, so have been preferred for many years. In some countries overseas there is now significant mite population resistance, and we are seeing the early stages of this now in New Zealand. However they are still the key element in most commercial beekeepers’ arsenal for dealing to varroa. Rotated with another treatment and used strictly as directed, resistance should not cause a problem. In regards to residues, synthetic pyrethroids are lypophilic which means they are soluble in oil, and hence beeswax. They will reach measurable levels in beeswax, and although there are no specified limits for beeswax, levels overseas have been seen at above 1ppm. They are hydrophobic so do not dissolve in water and thus don’t get into the honey, although if the honey is not well filtered to remove wax, the chemical may be carried in the honey on minute bits of wax. The maximum acceptable limit in honey for these chemicals is 0.05ppm. The tradename of this chemical class we sell is Apistan. Check this link for more information about it.

There are other classes of chemical strips available that can be well used in a rotating management plan with the synthetic pyrethroids, and that are just about as effective. Each has its advantages and disadvantages and it would be wise to talk to the vendor to determine which would be best for you.

In conclusion, varroa destructor is the single biggest threat to the life of your beehive. Many people come to look in their hive after six weeks of winter, and find it dead or dying and might think that it starved. More likely it died from direct varroa attack or the viruses that the sucking parasite introduces to the bees. If you wait to see varroa on a bee, or see bees with deformed wings or no wings, it is too late. The hive will invariably die. Don’t be a Sergeant Schultz and ‘see nothing’. Check your mite levels and use multiple techniques to deal with the problem.