Varroa mites (Varroa destructor) are one of the most serious threats to honey bee colonies worldwide. These tiny, parasitic mites weaken bees, spread diseases, and can ultimately lead to colony collapse if left untreated. In this blog post, we'll explore the history and evolution of Varroa mites, how they develop with honey bees, methods for assessing mite levels in your hive, and treatment options. We'll also touch on the ongoing debate between treatment and treatment-free beekeeping.

The History and Evolution of Varroa Mites

The Varroa mite originates from Asia, where it initially parasitized the Eastern honey bee (Apis cerana), a species native to that region. Over time, evolution allowed the Eastern honey bee to develop specfiic defenses against Varroa mites, including unique grooming behaviors and the ability to identify and remove infected brood. However, in the 20th century, Varroa mites made a jump to the Western honey bee (Apis mellifera), which did not have the same defenses. This shift has had devastating consequences for Western honey bee populations and they struggle to manage the mite infestation without the natural resistance that Apis cerana has developed.

*Molly showing what a varroa mite would look like if it were scaled up to the size of a human. GROSS!*

How Varroa Mites Develop with Honey Bees

Varroa mites reproduce inside the brood cells of honey bee colonies. Once a female mite enters a cell shortly before it is capped while the bee is in the larval stage. The female mite buries herself in the brood's food to avoid being detected by nurse bees. After the cell is capped, the mite begins laying eggs, typically producing one male and several female offspring. The male mite mates with his sisters inside the cell, ensuring the continuation of the mite population. As the bee develops, the mite larvae feed on the fat body of the bee pupa, weakening its immune system, stunting its growth, and often transmitting harmful viruses, like Deformed Wing Virus.

Fat bodies are essential organs involved in metabolism, nutrient storage, and detoxification. In Varroa mites, the fat bodies store nutrients like proteins and lipids, which are vital for reproduction and overall energy needs. They also play a key role in managing waste and processing toxins, much like the liver does in humans. This is why when Varroa mites feed on the fat bodies of developing honey bees, they significantly weaken the bee's immune system, reduce its energy reserves, and make it more susceptible to disease.

By the time the bee emerges, the mites have matured and are ready to continue the cycle, spreading further throughout the colony and beyond to other colonies by hitching rides on forager bees. This process can lead to a rapid increase in mite populations, devastating the hive if left unchecked.

Assessing Varroa Mite Levels in Your Hive

Monitoring Varroa mite levels is crucial for effective colony management. Here are some common methods to assess mite populations:

Sugar Shake Method: This involves collecting about 300 adult bees (roughly 1/2 cup) from the broodnest, coating them in powdered sugar, and shaking them in a jar. The sugar dislodges the mites, which can then be counted on a white surface. This method is non-lethal to the bees and provides a good estimate of mite infestation levels.
Alcohol Wash: Similar to the sugar shake, this method also involves collecting bees. However, the bees are placed in alcohol, which kills them but allows for a more accurate count of mites. This is our favorite mite washer.
Sticky Board Test: A sticky board is placed underneath a hive to catch falling mites over a period of time. The mites are then counted, giving an idea of the overall infestation level. While this method doesn't disturb the bees, it is often less accurate than sugar shakes or alcohol washes.
Visual Inspection: Checking drone brood for mites can also provide a visual indication of Varroa levels. However, this method is less comprehensive and shouldn't be relied upon solely.
As you gain more experience in beekeeping, you'll begin to recognize the signs of mite-infested brood. One common indicator is perforations or small openings in the pupal cappings. This often means that other bees in the colony have detected the presence of mites developing under the cappings and are attempting to remove or "abort" the infected brood in an effort to protect the hive from the spread of mites.

*The mites fall to the bottom of the container after doing a mite wash so you can calculate your hive's infestation rate.*

*An extreme example of uncapping behavior. We refer to these as "pickings". You can even see an adult mite on the top right of the photo.*

*Cole examining drone pupae for varroa mites. The mites prefer the drones extended 21 day development cycle as it allows them to produce more offspring.*

Treatment Options for Varroa Mites

There are a variety of treatment options for managing Varroa mites, ranging from chemical treatments to more natural methods:

Chemical Treatments: These include miticides such as formic acid, oxalic acid, and amitraz. These chemicals are applied directly to the hive and can be highly effective in reducing mite populations. However, overuse can lead to mites developing resistance, and there is concern about the impact of chemicals on bee health.
Mechanical Methods: These methods include techniques like drone brood removal. Since mites prefer drone brood, beekeepers can remove capped drone cells from the hive, thereby reducing the mite population.
Natural Treatments: Essential oils like thymol and organic acids can also be used as natural treatments. While these methods are less harsh on the bees, they may require more frequent application to maintain effectiveness.
Integrated Pest Management (IPM): Many beekeepers combine various treatments and strategies to manage mites more effectively. This holistic approach helps prevent resistance and minimizes the negative impact on the bees.

The Debate: Treatment vs. Treatment-Free Beekeeping

There is an ongoing debate within the beekeeping community about whether or not to treat hives for Varroa mites. Treatment beekeepers believe that interventions are necessary to protect colonies from Varroa infestation and prevent colony loss. They argue that without treatments, Varroa populations can spiral out of control and devastate the colony and spread to other nearby colonies.

On the other side, treatment-free beekeepers advocate for natural methods, allowing bees to develop their own defenses against mites over time. They believe that by refraining from chemical treatments, bees can evolve to become more resistant, much like the Eastern honey bee has. However, this approach carries the risk of colony loss, especially in the early stages as bees build natural resistance.

Whether you choose to treat or take a more natural approach, understanding the impact of Varroa mites and staying proactive in hive management is key to ensuring the survival of your bees.

Conclusion

It’s absolutely crucial to have a deep understanding of Varroa mites, their biology, their impact on honey bee health, and effective strategies for managing their populations in the hive. I highly recommend that all beekeepers explore Randy Oliver's blog, Scientific Beekeeping, and watch lectures by Varroa mite expert Sam Ramsey, who both offer invaluable insights on this topic.

Understanding Varroa Mites and Their Impact on Honey Bee Colonies