Varroosis Disease of Honey Bees

July 13, 2024

The threat of Varroosis to honey bee colonies is significant. Understanding and managing this disease is very necessary for every beekeeper. Come and get some knowledge about Varroosis diseases. You'll learn how to protect your hives and increase honey production.

What is Varroosis?

Folks consider Varroa destructor as a main factor of Varroosis disease.

Female Varroa mite is oval, brown, about 1.17 mm long and 1.77 mm wide;

The male is slightly smaller, oval, about 0.88 mm long and 0.72 mm wide.

Most adult mites parasitize between the abdomen segments of worker bees and drones. They suck the body fluids of adult bees.

Female Varroa mites will sneak into the brood cells to lay eggs, causing bee larvae to develop poorly. They weaken bee colony at the source. They endanger honeybee populations

You can picture what it would look like if varroa mites severely attacked a bee colony. If you have trypophobia, you would feel gross! You may find more than 20 mites on a single drone pupa and up to 12 on a worker bee.

Varroa mites are vectors for harmful viruses such as foulbrood and spore diseases. Even though we use miticides, honey bee virus remains at high levels.

This disease endangers honey bee populations. In the worst case, they can cause colony collapse, which messes with agricultural production.

History and Origin

Discovery of Varroa Mites

Researchers first identified Varroa in Southeast Asia in the early 20th century. These beekeeping pests first infested the Asian honeybee, Apis cerana. In the 1960s, they began infecting European honeybees (Apis mellifera), spreading rapidly worldwide. This spread was largely because of the movement of infested bees and beekeeping equipment.

Impact on Beekeeping Industry

In the early stages of attempting to manage this parasite problem, beekeepers employed chemical treatments, specifically Amitraz, a miticide. Nonetheless, their widespread presence and survival ability have caused enormous problems. Beekeepers had to accept that Varroosis was a constant problem. We cannot easily eradicate Varroa mites.

Over time, Varroa mites have greatly changed how we treat bees. We use chemicals, breed bees to resist mites, and improve how we manage hives.

Researchers focus on boosting honeybees' natural defenses by selectively breeding them and finding non-chemical ways to control.

Varroa Mite Biology

Varroa Mite Life Habits:

Varroa mites can only reproduce within sealed brood cells. Their development cycle includes three stages: egg, nymph, and adult mite. They primarily infest bee bodies and brood cells.

When spring comes, the bee colony has capped brood combs. Those annoying mites start reproducing. As the number of brood cells goes up, more Varroa mites infest them. The infestation hits its highest point in the summer.

In the fall, the colony's population declines and the number of brood cells decreases. Varroa mites continue to reproduce, shifting towards infesting a smaller number of cells and adult bees.

By the winter, Varroa mites cease reproduction and remain in the adult stage. They feed on bees' bodily fluids and overwinter with honeybees. That is to say, they can harm bee colonies throughout the entire year.

Varroa Mite Activity:

Temperature influences Varroa mite activity. In winter, bees must maintain a stable temperature within the beehive to ensure survival. This temperature also meets its survival requirements, but not its egg-laying requirements.

Varroa mites become active with temperatures above 18°C. To breed normally, the temperature needs to reach around 31°C. They are unable to reproduce in a broodless bee colony during winter. However, they can still coexist with honeybees during the winter.

Varroosis Symptoms and Diagnosis

Visible Signs in Bee Colonies

Observe the Head: Healthy bees exhibit lively and natural head movements. They give us a cute impression. If the head movements appear stiff and itchy, it may be a sign of infestation.

Observe Wings and Legs: Healthy bees have intact wings, spread their wings easily, and fly quickly. If you find young bees with damaged wings crawling on the ground, they cannot fly. This is Varroosis.

Diagnostic Methods

Mite Level Evaluation: Beekeepers should adhere to the principle of "prevention-oriented, integrated treatment." First, you need to analyze the severity of the bee mite infestation.

Regular monitoring helps you to judge whether your bee colonies have reached a threshold that requires Varroosis control. Beekeepers can use several methods to estimate mite infestation levels, for example:

- Sugar Roll: Dust sample bees with powdered sugar in a Varroa tester jar. Shake the jar, causing mites to fall off. Then we can count sugar-coated mites.

- Alcohol Wash: You also need the tool - Varroa tester jar. Take some sample bees and submerge them in alcohol. Varroa mites will sink to the bottom of the solution, and then you can begin counting. This simple detection is the most accurate of all.

- Sticky Boards: The Varroa board has a sticky substance below a screened bottom. Placed under the beehive, these boards catch falling mites. This method only roughly monitors an infestation rate because it does not take the honeybees' population into account.

After completing an assessment of your bee colonies, you must master when to treat Varroa mites. This will allow you to save your colony at the optimal time.

Threats to Bee Health and Colony

Physical Harm: Varroa mites primarily feed by sucking the hemolymph and bodily fluids from the surface of honeybees. They take away necessary nutrients from the bees. This makes them weak, grows slowly, and even causes them to die early.

Infested honey bee larvae may experience stunted development, resulting in weight loss and deformed wings and legs. They may also lose the ability to fly.

Transmission of Viruses: Varroa mites are vectors for several harmful viruses. Deformed Wing Virus (DWV) and Acute Bee Paralysis Virus (ABPV), etc., are popular. Varroa-infested colonies transmit viruses through their saliva.

These viruses can disrupt the immune system of bees, which makes them physically weaker. This heightened risk makes it easier for them to contract secondary infections and diseases.

Management and Control Strategies

In beekeeping, Varroa mite treatments are often not singular. Treatments typically involve alternating multiple methods.

Common Acaricide: Regular substances such as amitraz, fluvalinate, coumaphos, etc. are chemical treatments.

Organic Miticides: Mild chemical substances include oxalic acid, formic acid, thymol, etc. In the beekeeping industry, we regard these products as organic medication.

Pros and Cons:

Chemical treatments exhibit efficacy in diminishing mite numbers. Nevertheless, these treatments also possess certain drawbacks.

One drawback is the development of miticide resistance. Another issue is the potential harm to bees. Additionally, there is a risk of pollution of hive products.

Organic acaricide is generally safer for the environment and bee products. However, applying organic treatments often requires large doses. This means more labor and careful handling. Moreover, they may not be as effective as synthetic chemicals.

Non-Chemical Methods

Mechanical Controls: Techniques such as drone brood removal (where drone brood, which attracts more mites, is removed and destroyed). Using screened bottom boards to trap falling mites can help reduce their populations.

Biological Controls: Breeding mite-resistant bee strains is a trending research direction in recent years. Using organisms that hunt Varroa mites offers a promising non-chemical method.

Challenges and Future Directions

Resistance to Treatments

Development of Acaricide Resistance: Overuse of chemical treatments has led to resistant mite populations. These treatments become less effective.

Need for New Control Methods: Research into new and innovative hive management strategies is a constant need.

Research and Innovations

Some points of view are around sustainable beekeeping. The biological method of artificial brood interruption, when combined with treatment, offers the highest level of control, effectively limiting Varroa population growth. Methods such as queen caging, drone brood removal, total brood removal, and trapping comb are used in this approach.