Varroa Mite in Honey Bee Colonies

(Varroa destructor – parasitic mite of honey bees)

Introduction

The varroa mite (Varroa destructor) is widely considered the most destructive parasite affecting honey bee colonies today. Beekeepers in Europe, the United States, Australia, and Asia all deal with this annoying and destructive pest, and is well know that unmanaged infestations almost always lead to colony collapse cause very big economic loss.

From my experience working in pest control and managing small apiaries (i have 15 colonies myself), varroa mites behave like a chronic parasite that slowly drains the colony strength. Colonies may look healthy during spring but if they do not get the treatment they need they will collapse suddenly in late summer or autumn once mite populations explode.

Varroa mites attack the European honey bee (Apis mellifera) and reproduce inside brood cells. They weaken bees directly and also transmit dangerous viruses such as Deformed Wing Virus, Acute Bee Paralysis Virus, and Sacbrood Virus.

Because of this dual damage—parasite plus virus transmission—varroa mites are now considered the primary cause of honey bee colony losses worldwide.

Other pests can also affect colonies and may appear together with varroa infestations, like the Small Hive Beetle (Aethina tumida), Greater Wax Moth (Galleria mellonella), Lesser Wax Moth (Achroia grisella), and the other awful parasite Tropilaelaps mites (Tropilaelaps clareae).

Understanding the biology and management of varroa mites is essential for every beekeeper.

Identification

Varroa mites are relatively easy to recognize once you know what to look for.

Key identification features:

• Scientific name: Varroa destructor

• Size: about 1.1 mm long and 1.5–1.7 mm wide

• Color: reddish-brown

• Shape: flattened oval body

• Legs: eight legs (like all mites)

The mites look like small brown sesame seeds attached to a bee’s body.

Most of the time they hide:

• between abdominal segments

• under the thorax

• inside brood cells

Because of this behavior, many infestations go unnoticed until the colony becomes weak.

According to a government technical guide on varroa mites, the parasite is extremely widespread and has established populations in Asia, Europe, Africa, the Americas, and New Zealand. Almost everywhere

Biology & Ecology

Varroa mites reproduce only inside capped brood cells especially those of the male cells.

The reproductive cycle works like this:

1. A female mite enters a brood cell containing a bee larva shortly before the cell is capped.

2. Once sealed, she begins laying eggs.

3. The first egg becomes a male mite, while the rest become females.

4. The offspring feed on the developing bee pupa.

5. When the adult bee emerges, the mother mite and daughters leave the cell and infest other bees.

Mites strongly prefer drone brood, because drones develop longer than worker bees.

• Worker development: ~21 days

• Drone development: ~24 days

This extra time allows the mite to produce more offspring per cycle, accelerating population growth.

A female mite can reproduce multiple times during her lifetime. When brood is present from autumn till winter, mite populations can grow exponentially within one season and can destroy the colony.

Global Distribution

Today, varroa mites exist in almost every major beekeeping region of the world.

Important regions affected:

• Europe

• North America

• South America

• Asia

• Africa

• New Zealand

In some countries, many wild honey bee colonies disappeared after the arrival of varroa mites. Untreated colonies typically collapse within 1–3 years or less. The parasite originally evolved with the Asian honey bee (Apis cerana). That species developed natural resistance mechanisms.

When varroa mites jumped to Apis mellifera, the western honey bee had no natural defense and still not have any, which explains the severe global impact.

Risks and Damage

Varroa mites damage honey bee colonies in several ways.

1. Direct parasitic feeding

The mites feed on fat body tissue of bees, which functions similarly to a liver and immune system.

This causes:

• weakened bees

• reduced lifespan

• reduced immune function

2. Virus transmission

Varroa mites act as vectors for many viruses, including:

• Deformed Wing Virus

• Israeli Acute Paralysis Virus

• Kashmir Bee Virus

• Sacbrood Virus

More than 20 viruses have been linked to varroa infestations.

3. Parasitic Mite Syndrome

Heavy infestations lead to a condition known as Parasitic Mite Syndrome (PMS).

Typical symptoms:

• irregular brood pattern

• dying larvae

• collapsing colony population

4. Colony collapse

Without treatment, varroa mites usually kill colonies within months or a few seasons.

Signs of Infestation

Beekeepers should monitor colonies regularly because mites can be hard to detect.

Common signs include:

Visible mites on bees

Occasionally you can see reddish mites on:

• the bee thorax

• abdomen segments

• drone pupae

Deformed bees

Bees emerging with:

• twisted of deformed wings

• shortened abdomen

• weak movement

These symptoms are usually caused by Deformed Wing Virus transmitted by mites.

Weak colonies

Typical symptoms:

• declining population

• spotty brood pattern

• slow honey production

Sudden autumn collapse

Many colonies collapse in late summer or fall after mite populations reach critical levels.

Monitoring and Detection Methods

Professional beekeeping relies on regular monitoring.

The most reliable methods are:

Sugar Shake Method

• Collect ~200–300 bees form the colony and put them in a jar with a lid.

• Coat them with powdered sugar.

• Shake the bees an count the mites that got off.

Bees survive this method and can be returned to the hive.

Alcohol Wash

This method is more accurate but kills the sampled bees and personally i don't do it cause i don't like killing bees.

Steps:

1. Collect ~300 bees from brood frames.

2. Wash them in alcohol.

3. Count the mites that fall off.

Sticky Board Monitoring

You can buy a sticky board and place them under the hive.

Falling mites are counted after 24–72 hours.

This method estimates the total mite population in the colony but is not that accurate.

Control and Prevention Methods

Effective management requires an Integrated Pest Management (IPM) approach.

This combines several techniques rather than relying on chemicals alone.

Mechanical methods

Common non-chemical techniques include:

• Screened bottom boards to allow mites to fall out of the hive

• Drone brood removal (mites prefer drone brood)

• Powdered sugar dusting

These methods help reduce mite populations but rarely eliminate them completely.

Resistant bee strains

Some bee strains have been developed that show partial resistance:

• Russian honey bees

• Varroa Sensitive Hygiene (VSH) bees

• Minnesota hygienic stock

These bees detect and remove infected brood. I haven't check them but i don't expect any miracles.

Apiary management practices

Important preventive measures:

• avoid exchanging contaminated equipment

• maintain strong colonies

• reduce drifting between hives

• inspect colonies regularly

Advanced / Professional Approaches

Professional beekeepers often use chemical treatments when mite populations exceed safe thresholds.

Common treatments include:

• Amitraz-based products

• Formic acid treatments

• Oxalic acid treatments

• Thymol-based products

The formic acid, the oxalic acid and the thymol-based products are considered friendly treatment but all of these treatments must be used carefully.

Important rules:

• never apply during honey flow

• rotate treatments to prevent resistance

• You must follow legal pesticide regulations of your country.

Improper treatment can contaminate wax or honey and may harm bees.

Cultural and Historical Context

The varroa mite became a global problem during the second half of the 20th century.

It originally parasitized Apis cerana in Asia, where colonies evolved defensive behaviors.

Once the mite spread to Apis mellifera, global trade of bees allowed it to move quickly between continents.

Today, modern beekeeping practices assume that varroa management is a permanent part of beekeeping, similar to disease management in livestock.

FAQ
What is the varroa mite?

Varroa mites are parasitic mites that attack honey bees and reproduce inside brood cells. They weaken bees and spread viruses.

How do varroa mites spread between colonies?

They spread through:

• drifting bees

• robbing behavior

• swarms

• movement of hive equipment

Can a colony survive without treatment?

Usually no. In most regions untreated colonies collapse within a few years due to mite population growth.

What is the best way to detect varroa mites?

The most reliable methods are:

• alcohol wash

• sugar shake

• sticky board monitoring

These techniques estimate mite levels in the colony.

Why do mites prefer drone brood?

Drone brood develops longer than worker brood, giving mites more time to reproduce.

Are chemicals always necessary?

Not always, but most commercial beekeepers use Integrated Pest Management (IPM) combining monitoring, mechanical methods, and selective chemical treatments when thresholds are exceeded.

Can varroa mites affect honey production?

Yes. Infested colonies produce less honey because the bee population becomes weak and unhealthy.

Are varroa mites the main cause of colony collapse?

In most regions, yes. Varroa mites and the viruses they spread are considered the leading cause of honey bee colony losses worldwide.