Greatest Threat to Honey Bees: Varroa Mites

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Honey bees face many challenges in our modern world.  Pesticide use in both commercial agriculture and household gardens and the destruction of habitats are concerning problems that honey bees face. However, the greatest threat to honey bees around the world is a tiny villain, barely visible to the naked eye. Fittingly named, Varroa Destructor, they are commonly known as varroa mites is the biggest challenge faced by honey bees in the world.

Know Your Villain

Varroa Destructor is an external parasite member of the arachnid species, along with ticks and spiders.  While they are visible to the naked eye, they are extremely tiny, only about 1 to 1.8 mm long. They are round and are brown or reddish in color.  They carry viruses and pathogens that threaten honey bees development. Varroa mites have 8 legs. They feed by piercing and sucking on the body of the bees. While the varroa mite is tiny from a human perspective, they are quite large from the perspective of a honey bee measuring about 1/2″ in length.

Varroa mites are true parasites therefore they can not live long-term away from their host species. They travel and feed off of adult honeybees. Therefore, they easily travel from bee to bee within a normally populated colony. To reproduce, adult varroa mites enter the brood cells of honeybee colonies just prior to being capped. Once capped, the mites lay eggs inside and feed off the developing brood. Once they hatch, the young mites breed while still in the capped brood cell.

Varroa mites are especially fond of drone cells. The cells themselves are larger allowing for more space to reproduce. Drones also have a longer gestation period, allowing additional time to reproduce. Queen bees emerge from their cells in 15 to 16 days, worker bees emerge in approximately 21 days, while drones require 24 days to emerge.

Continuing Cycle

Young bees may survive the mite damage, but are weakened and will have shorter lifespans. Some young bees may be unable to fly being infected with a virus called Deformed Wing Virus. Once the bees hatch, they release the young varroa mites within the hive where they continue to infest the colony. Honey bees are most vulnerable during the winter, colonies weaken by varroa mites infestations are less likely to survive their most challenging season of the year.

Varroa mites are present in almost all the honey bee colonies in the United States and most of the world. Colonies that go untreated ultimately will die from infestation within 2 to 3 years. Since I am a bit of a science nerd, I enjoyed this video on the reproduction cycle of the varroa mite.

Mite Counts

Varroa mites are extremely small and reside primarily in the capped brood cells. It may be too late to counteract the infestation once it is easily visible within the hive. Mite counts are a way to estimate the level of infestation that a beekeeper might be experiencing. There are several methods to complete a mite check.

Sticky Boards

If you have screen bottom boards in your hives, sticky boards are an option. These boards are exactly what they seem, they are sticky! Place the boards at the bottom of the hive beneath the screen bottom. When the varroa mites fall off the bees they become stuck on the boards. Beekeepers can count the number of mites found on the boards after a few days and determine their infestation level. This method of mite counting does not harm the bees.

Sugar Shake

The powdered sugar method is another popular method that does not harm the bees. Approximately 300 bees are placed inside a mason jar with a screen lid. Powdered sugar is sprinkled over the live bees. The bees will need to be covered in powdered sugar and then shook to knock the mites off of the bees. . The powdered sugar brushes the mites off of the bees. While the bees are still contained in the jar, sprinkle the powdered sugar and mites through the screen lid. The bees can be released to clean themselves of the powdered sugar. Carefully inspect the powdered sugar and count the mites found to determine the infestation level.

Alcohol Wash

The alcohol wash method of mite counting is similar to the sugar shake method except it kills the bees used in the sampling. It is considered a more accurate method of mite counting. Place a half cup sampling of bees, about 300 bees, into a mason jar with a screen lid. Pour enough rubbing alcohol into the jar to completely cover the bees by about an inch. Cover the screen lid and shake to wash the mites off of the bees. Pour the alcohol into a bowl through the screen lid, and dispose of bees. Count the number of mites to determine the infestation level. We have used this method ourselves to determine our mite counts.

Understanding the Varroa Mites Count Results

Varroa mite counts are based on groups of 100. The most common test group is a half cup of bees, which is estimated to be about 300 bees. After counting the number of mites found, divide the number by 3 to determine the number of mites per 100 bees.

Honey bee colonies are treated when the infestation levels reach 2% to 5%. A colony with a 5% infestation level would indicate the colony is in crisis and needs immediate intervention. Since honey bee colonies have thousands of bees, finding only a few mites in a mite count would indicate that mites have reached a treatable infestation level.

According to the University of Florida, the rule of thumb is to treat your colony if you find 3 or more varroa mites using the powdered sugar or alcohol wash methods or more than 40 mites if using the sticky board method.

The average 10-frame hive has between 30,000 to 60,000 bees. Based on finding just 3 mites in the 100 bee test group, can indicate approximately 900 to 1,800 mites in a colony of 30,000 to 60,000 bees which is a 3% infestation.

Reporting Results

If you would like to help researchers understand and monitor varroa mite infestation levels you can report your mite counts at MiteCheck. They do have some specific guidelines so be sure to research the requirements so that you can accurately participate in the survey.

Treating Honey Bees for Varroa Mites

Due to the small percentage that is considered an infestation level in honeybee colonies, it is recommended and commonly practiced that beekeepers routinely treat their honeybee colonies for varroa mites. In the past, we have conducted mite checks which have indicated that the bees needed treatment. To best protect our colonies, we treat our honeybee colonies with a chemical treatment three times a year.

Come Along

Treatments Used at Kowalski Apiary

There are several approved chemical treatments used to treat honey bees. The bees should be rotated through different chemical treatments so that the mites do not become resistant to treatment. We have used a couple of chemical treatment brands.

Apivar

Apivar is an easy chemical treatment that is done by placing strips into the brood boxes. The strips are white plastic strips, easily placed in the brood boxes. The strips are left in the boxes for two brood cycles. Apivar should not be used when the honey supers are on the hives. Please read the instructions carefully to be sure to use them appropriately to not contaminate your honey. We used Apivar for our mite treatments in our first year of beekeeping.

Hopguard

HopGuard3 is an all-natural treatment method we are using for the first time. It is also easy to use but quite a bit messier. It smells bad and riled the bees up pretty quickly. Philip asked me to assist so that I could handle the strips while he placed them into the brood boxes, however, the bees got somewhat aggressive when we started putting the strips in so he did the job solo. I still get nervous when the bees get riled up and they know it!

The benefit of using HopGuard is that it is food safe and is safe to use during the honey flow. Unlike other varroa mite treatment chemicals, the honey supers do not need to be removed from the hive boxes. Most of our hives don’t currently have honey supers since we are in a dearth, but still, I prefer an option that is safe around our honey. As always, be sure to read the instructions and use them as directed.

Other Chemical Treatments

There are many other treatment options, I found the Carolina Honeybees website to be an excellent resource to determine the options available to beekeepers.

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HopGuard3

Philip’s Beekeeping Glasses Really helps to see the eggs in the frames.

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Sources of Information

I prefer to use all my own photos on the blog, however, I couldn’t find a single bee image that had a varroa mite on the bees. This is a good thing! All the varroa mites images in this post are from Canva, a stock photo service that I subscribe to.

Check out our very first honey bee rescue.