Testing for Varroa Mites

I have received a lot of emails, calls, and messages about varroa this year. In our own yards, the lack of nutrition and harsh conditions have set the stage for tougher than normal varroa hits, and I suspect many of you are seeing the same.  Though I can’t possibly answer all the questions here, today I want to provide you with some resources and tips for identifying and addressing varroa concerns.  

Varroa mites are an external pest found on adult honey bees and on drone and worker pupae.  All the varroa that are present outside of brood cells are female adult varroa, and they are oval-shaped reddish-brown mites that are 1.5 mm wide. To me they look like tiny little ticks (And similar to ticks, they spread diseases through their bites.) 

Unfortunately, although varroa mites are visible to the human eye, it’s impossible to assess the number of varroa in a hive with a visual inspection only. There are signs that your hive is experiencing high mite counts, which exhibits itself in the form of a disease called Parasitic Mite Syndrome.  Some signs include small puncture holes in the capped brood, or the bees uncapping the pupae altogether (a phenomenon called bald brood). This is evidence that your bees are uncapping the cells to remove the varroa from the brood, This trait, known as Varroa Sensitive Hygiene (VSH) is a highly desirable trait in honey bee colonies.  Other signs include a swift and significant drop in your honey bee population, a spotty brood pattern, and pupae that appear to have been chewed down. Deformed Wing Virus is another virus associated with varroa mite, and it causes deformations in the wings of adult honey bees.  Bees suffering from Deformed Wing Virus look as if their wings have been singed with fire. 

Testing for Varroa

Several tests can help you assess the infestation level of varroa in your hive.  Two of these tests involve taking a sample of ½ cup of nurse bees, roughly 300 bees, from your colony and placing them in a jar with either alcohol or powdered sugar with hardware cloth as a lid.  The alcohol or powdered sugar will knock the mites of the bees and you are then able to shake the jar, and the mites, out and count the number of mites found.  The sugar shake test does not kill the bees, but the alcohol test does. However, the alcohol test has been shown to be more accurate. The test is fairly easy to perform, and you just need a few supplies. You can find videos of how to perform a sugar shake test on our YouTube channel.

Examining the Results

Once you have the total number of mites found in your sample, you can then extrapolate the results to the rest of the colony. For example, if 3 mites are found among the 300 bees, that is a 1% infestation rate. If 9 mites are found, that is a 3% infestation rate. As with all things honey bees, you will find a wide range of recommendations of when to take action, but most recommend intervention around the 3% infestation rate or higher (9 mites or more in your 300 bees sample).  

What now?

When thinking about varroa management, it’s important to understand and accept that eradication of pests is rarely attainable, and will likely never be possible with varroa mite. Looking back at the United States’ reaction to varroa, we see that more than a decade of heavy toxic chemical treatments did not result in eradication, but rather just produced mites resistant to some of those treatments.  Therefore, learning to manage your hives while accepting that some level of varroa mites will be present  is critical. As with all pests and disease, I encourage beekeepers to try to focus on physical, mechanical, and cultural practices and prevention methods before turning to any chemical treatments. This means enacting methods and practices that focus on prevention and are less toxic to you, the environment, and the bees.  Also know that you will likely want to employ several different methods for preventing and managing varroa, as there is no silver bullet answer. I’ll review just a few ways to control for varroa, but know that each of these may not be right for you and your bees, but are provided for your information.  Also, I strongly recommend you check out the Honey Bee Health Coalition’s Varroa Management Decision Tool. This tool will guide you through a series of questions to learn more about your beekeeping philosophies and style and state of your hive to make recommendations on different options. 

Cultural: Some examples of cultural practices to control for mites include: 

• Good genetics: It is critical to make sure you have genetics with the VSH trait to start your apiary. 
• Site hives with good sun exposure: Mites are temperature sensitive, so siting hives with plenty of sun and good ventilation can help with mite loads.  

Physical and Mechanical:  While there are no traditional trap methods for controlling varroa, there are a few other mechanical practices you may decide to employ: 

• Cull drone brood: Some beekeepers choose to cull, or remove, drone brood from their hives.  Since varroa are 10-12 times more likely to reproduce in drone cells, this can be an effective method of removing developing varroa.  You can even purchase a drone brood frame, which encourages bees to build drone cells where the queen will lay drones that you can then remove. Just keep in mind that you want to watch this frame carefully, and remove it before the drones emerge (along with the varroa). I do some culling in yards where I think the number of drones in a hive may be “excessive”, but I don’t cull all drones from my apiaries because the genetics of my bees are highly desirable and I want those genetics to spread! So, how do you cull the drones? I simply cut the cells out of the frame with my hive tool. (Pro tip: chickens love to eat drone brood.)
• Screen bottom boards:  Some beekeepers choose screen bottom boards so that if the bees groom mites off of one another, they fall through the screen board out of the hive. This is a great example to demonstrate that not all tools are right for all beekeepers.  I do not use screened bottom boards in my hives, as I believe bees do a better job of regulating temperature with solid bottom boards here in Texas.  Screened bottom boards often have an insert so that you can turn a screened bottom board into a solid bottom board at different times of the year, for example, in the winter months. 
• Comb cycling: As we come out of the cold weather months, you can employ comb cycling, which involves removing 2 of the oldest frames of comb in your brood nest.  This hygienic action helps remove built up pesticides and pathogens in the hive. 
• Brood breaks: Because varroa mites are reliant upon honey bee brood to mate, a period of time when there is no brood in the hive can interrupt the reproduction cycle of the bees. This is what we call ‘breaking the brood cycle” and can be done a number of ways. One way is to kill your queen, and then buy a queen from a breeder (make sure to find a VSH queen) and install her in your hive a few weeks later. Make certain to cut down all the developing queen cells before you install your new queen (and before they can emerge!). You can also allow the hive to rear a new queen, but if you are concerned about the genetics of your hive you may want to try to find a breeder queen with the VSH trait.  You can also cage your queen in a queen cage to prevent her from laying for a few weeks. 
• Thermal treatments: Research has found that slightly raising the temperature of the brood nest can kill varroa mites.  This is a fairly new option to beekeepers, and you can buy a contraption that will raise the temperature of the brood nest for several hours to a level that stresses the mites but that the honey bees can manage. 

Chemical: A number of chemical controls exist, from the less toxic treatments created from essential oils to a more toxic class of miticides.  It’s important to note that in the United States, mites have developed resistance to  a number of chemical treatments from overuse.  This is why it’s important that if you do decide to use any treatments, no matter how organic, you are using this as a true treatment and not a preventative.  Refrain from treating all hives based on a calendar schedule, and rather use a treatment on a colony only monitoring has unturned a mite load that exceeds your acceptable threshold. Also, a number of these treatments cannot be used when honey supers are on the hive or with brood present, and some are temperature dependent.  The Honey Bee Health Coalition has a mite management tool that acts as a sort of decision tree. You can input characteristics of your colony (if there is brood present, for example) and it will share a number of options. 

Two Hives Honey is a treatment-free operation, but that does not mean we can ignore the presence of varroa or that we don’t have to battle varroa from time to time.  We rely heavily on genetics and brood breaks to control varroa in our apiaries, and have been very successful avoiding chemical treatments as a result.  

It’s also important to note the incredible amount of ongoing research on varroa and its effect on honey bees. Only very recently scientists discovered that varroa actually didn’t feed on the blood of honey bees, but rather they feed on the fat bodies. And a lot of recent research has been done on the positive effect of mushrooms and their ability to aid honey bees in fighting the diseases that are caused by varroa mites. What we know about managing, treating, and preventing varroa changes relatively frequently, so it’s important to find ways to stay abreast of new developments.