Varroa Mite Monitoring: How to Test Your Honey Bee Colonies

Why Monitoring Varroa Mites Matters

A colony can look healthy and active at the entrance while carrying a Varroa infestation high enough to compromise its survival. Bees continue to forage, cluster and raise brood even as mite populations rise — often until the damage to the developing worker generation becomes visible in late summer or fall, at which point recovery is much harder.

Visual inspection at the hive entrance or on frames will not give you a reliable estimate of how many mites are present. Mites spend a significant portion of their reproductive cycle inside capped brood cells, where they are entirely invisible. Even during the phoretic phase on adult bees, the proportion of the colony carrying visible mites tells you very little about total population size.

Monitoring fills that gap. It allows you to:

• Assess infestation levels before deciding whether to treat
• Verify that a treatment achieved the expected result
• Detect rising mite levels between treatments before they reach a critical threshold
• Compare results across colonies and across seasons

One test taken once a year is not enough. Varroa populations change as the colony’s brood cycle progresses. Testing at relevant points throughout the season gives you the information you need to respond at the right time.

What Is Varroa Mite Monitoring?

Varroa mite monitoring is the practice of sampling your colony to estimate the current infestation level. It involves collecting a representative sample of bees or placing a monitoring device in the hive, then counting the mites present and interpreting the result against applicable guidelines.

Why You Cannot Rely on Visual Inspection

Even experienced beekeepers with good eyesight cannot reliably estimate a colony’s Varroa load by looking at bees. Adult female mites are small — approximately 1.1 mm wide and 1.6 mm long — and reddish-brown in colour. On a dark bee, they can be very difficult to spot, particularly during a routine hive inspection.

More importantly, a large proportion of mites in a colony with active brood are inside capped cells at any given time. You can examine every frame and see no visible mites on adult bees while the colony’s infestation level is already above the threshold that warrants treatment. Absence of visible mites is not evidence of a low or safe infestation.

Monitoring Before and After Treatment

Monitoring serves two distinct purposes in a Varroa management plan.

Before treatment: A baseline measurement helps you assess whether the current infestation level meets the threshold that applies to your colony, your province and the current season. Treating based on guesswork can mean treating too late, too early, or concluding that no treatment is needed when one actually is.

After treatment: A follow-up test confirms whether the treatment achieved the expected reduction. Not every treatment works as expected in every situation. Environmental conditions, product application, the presence of capped brood, and other factors can affect outcomes. Monitoring after treatment identifies cases where the infestation remains elevated and a reassessment may be needed.

The Main Methods for Monitoring Varroa Mites

Three methods are used most commonly by beekeepers to estimate Varroa infestation levels. They measure different things, require different equipment, and have different advantages and limitations.

How to Perform an Alcohol Wash for Varroa Mites

The alcohol wash provides a quantitative estimate of the proportion of phoretic mites in a colony. It is widely used because it is relatively straightforward to perform, requires minimal equipment, and produces a result you can compare across multiple tests and colonies.

What You Need for an Alcohol Wash

• A collection container or sampling jar
• A wash device with a mesh or screen lid for separating mites from bees
• Isopropyl alcohol (rubbing alcohol) or an alcohol wash solution as specified by the kit or protocol
• A light-coloured collection tray or container to count mites against
• A notebook or monitoring record sheet

How to Collect a Representative Sample

The quality of your result depends on where and how you collect the sample. A sample of approximately 300 worker bees from the brood nest is commonly used — this is the approach described in Ontario’s provincial monitoring guidance. Always follow the sampling protocol recommended for the kit or method you are using.

Collect the sample from a frame covered with nurse bees near the brood nest. These bees are more likely to carry phoretic mites than bees at the entrance or on honey frames. Shake or brush bees directly into the sampling container.

How to Count the Mites

After adding the alcohol solution, close the lid and shake gently for 30–60 seconds to separate the mites from the bees. Pour the liquid through the mesh into a light-coloured tray. The mites are small and reddish-brown; count them against the pale background of the collection tray. If counting in the field is difficult, collect the wash liquid in a sealed container and count later indoors.

How to Calculate the Varroa Infestation Percentage

This result is an estimate based on the sample collected, not a count of every mite in the colony. Sampling variation, timing within the brood cycle, and the proportion of mites currently inside capped cells will all affect what the sample reflects. A single measurement gives you a useful data point; repeated measurements across the season give you a trend.

Advantages and Limitations of the Alcohol Wash

• Advantages: Produces a consistent percentage result that can be compared across colonies and test dates; gives a clear, calculable figure; results are available immediately in the apiary.
• Limitations: The sampled bees do not survive; results depend on collecting an accurate and representative sample; the method detects mites on adult bees but does not count mites currently inside capped brood cells.

Monitoring Equipment — Alcohol Wash

How to Use a Sticky Board for Varroa Monitoring

What Is a Varroa Sticky Board?

A sticky board is a flat board with an adhesive surface that is placed beneath the hive’s brood box, usually below a screened bottom board. As mites fall naturally from adult bees — through grooming behaviour, movement, or the bee’s own activities — they drop onto the sticky surface and are held there for counting.

The board must be configured correctly for your hive. When used with a screened bottom board, a protective mesh between the bees and the sticky surface is typically needed to prevent bees from reaching and becoming stuck to the board.

How Long Should a Sticky Board Stay in the Hive?

Ontario’s provincial guidance describes monitoring periods of 24, 48, or 72 hours. Longer monitoring periods generally provide a more reliable estimate of mite drop, because daily variation in mite fall — due to weather, colony activity, and other factors — is averaged out over a longer interval.

Record the exact number of days the board was in place. This is essential for calculating the daily mite drop rate, which is the figure used to compare results across tests and colonies.

How to Calculate Mite Drop per 24 Hours

What Can a Sticky Board Tell You?

A sticky board count is useful for:

• Tracking trends in mite fall over multiple monitoring periods in the same colony
• Observing mite drop after a treatment (a significant increase in mite fall shortly after applying a treatment can indicate that the product is working)
• Identifying a sharp change that suggests the colony warrants closer investigation

What Are the Limitations of Sticky Boards?

Sticky board results are affected by several variables that make them harder to interpret in isolation:

• Colony size and population — a larger colony may show a higher mite drop simply because more bees are moving through the hive
• Bee grooming behaviour — some colonies groom more actively than others, which affects how many mites fall off
• Ants and other insects — they can remove mites from the sticky surface between when it is placed and when it is retrieved, which leads to undercounting
• Length of the monitoring period — a 24-hour count on a cold, quiet day may look very different from a 24-hour count during active foraging

Monitoring Equipment — Sticky Board

Is the Sugar Roll Method Reliable?

How the Sugar Roll Works

The sugar roll uses powdered icing sugar to coat a sample of bees, causing mites to detach. The bees are then rolled or shaken over a mesh screen or into a container, and the mites that fall through the mesh are counted. The bees can be returned to the hive after sampling, making this a method that does not require sacrificing the sample.

Sugar Roll vs. Alcohol Wash

The sugar roll is sometimes preferred by beekeepers who are reluctant to sacrifice bees or who are working with small colonies where sample loss is a concern. In those situations it can provide some indication of phoretic mite levels.

However, several factors limit the reliability of sugar roll results compared to alcohol wash:

• Mite detachment depends on the bees being adequately coated with sugar, the rolling technique, and the ambient temperature — results can vary considerably between tests and between individuals
• In warm conditions, the sugar may clump and coat the mites rather than dislodging them
• Studies comparing the two methods have found that the sugar roll generally recovers a lower proportion of mites than the alcohol wash, which can lead to underestimating the actual infestation level

Monitoring Equipment — Sugar Roll

How Often Should You Monitor Varroa Mites?

No single monitoring schedule works for all Canadian provinces. The timing that makes sense in British Columbia differs from Alberta, Manitoba, Ontario or the Atlantic provinces, because colony development, brood cycles and the timing of fall treatments all follow regional climate patterns. What matters is testing at points in the season where the results will inform a practical decision.

Spring Monitoring

Early spring monitoring, once the colony has resumed brood rearing and bee numbers have started to recover, gives you a baseline for the new season. If a fall treatment was applied before winter, a spring test can show whether mite levels were successfully reduced and whether the colony enters the season in good condition.

Summer Monitoring

During the main brood-rearing season, Varroa populations can grow quickly because abundant capped brood provides continuous reproductive opportunity for the mites. Regular summer monitoring — at least once during the peak brood period — helps you identify whether the infestation is increasing faster than expected and whether an intervention may be needed before the critical late-summer period.

Late-Summer and Fall Monitoring

The late-summer monitoring window is arguably the most important of the year. The worker bees that are raised in late summer and early fall will form the winter cluster and carry the colony through to spring. High Varroa infestation during this period — compounded by the additional mites entering from collapsing colonies in the surrounding area — can severely compromise the health and longevity of these bees.

Testing in late summer, before fall treatments are applied, tells you whether intervention is needed and helps you time the treatment correctly. Testing again after the treatment confirms the result.

Monitoring After Treatment

After applying a Varroa treatment, a follow-up test confirms whether the intervention achieved the expected result. The appropriate interval between treatment and follow-up monitoring will depend on the product used, the method applied, and current brood conditions — consult the product label and applicable provincial guidance rather than using a fixed number of days.

If mite levels remain elevated after treatment, the colony should be assessed further. Do not assume that the treatment worked without checking.

Understanding Varroa Treatment Thresholds in Canada

What Is a Varroa Treatment Threshold?

A treatment threshold is a reference point used to help decide when an infestation level is high enough to warrant a control intervention. It is not a biological absolute — a colony at exactly the threshold is not guaranteed to be in danger, and a colony just below the threshold is not guaranteed to be safe. The threshold is a decision-support tool based on research and field experience, not a fixed law of nature.

Why Thresholds Differ by Province and Season

Thresholds can vary depending on:

• The province or territory, because provincial beekeeping authorities set their own guidance based on local research and conditions
• The season — a mite level that may be acceptable in early summer may require immediate action in late summer, when the winter bee generation is being raised
• The monitoring method used — an alcohol wash percentage and a sticky board daily mite drop are not calculated or interpreted the same way
• The overall health of the colony and the presence of other stressors

Where to Find Current Canadian Recommendations

Treatment thresholds for Varroa management are set and updated at the provincial level. Rather than publish a single threshold table here — which could become outdated and does not account for provincial differences — we direct beekeepers to the current guidance for their region:

• Ontario: Ontario Ministry of Agriculture, Food and Agribusiness — Varroa Mites
• All provinces: Canadian Food Inspection Agency — Honey Bee Biosecurity Guide and your provincial beekeeping association or extension service

Common Varroa Monitoring Mistakes to Avoid

Relying on Visual Inspection Alone

Not seeing mites on your bees does not mean the colony has a low infestation. Mites inside capped brood cells are invisible during a routine hive inspection. Always use a sampling method to get a measurable result.

Sampling Too Few Bees

A sample that is smaller than the recommended size can produce a result that is not statistically representative. If you follow the Ontario protocol of approximately 300 bees, you can compare your results consistently across tests. Sampling 50 or 100 bees may produce misleading results that either overstate or understate the infestation.

Comparing Results From Different Methods

An alcohol wash infestation percentage and a sticky board daily mite drop are not directly comparable. Each method measures something different. Evaluate each result against the guidelines that apply to that specific method and the current season.

Testing Only Once a Year

A single measurement in spring, or a single measurement in fall, cannot describe the full arc of a colony’s Varroa history through the season. Mite populations change as brood production rises and falls. Testing at multiple points allows you to detect problems before they become critical.

Assuming the Treatment Worked Without Checking

A correctly applied treatment does not always achieve the expected result in every colony. Residual mites inside capped brood at the time of treatment, environmental conditions, and product efficacy can all affect the outcome. A follow-up monitoring test tells you whether the treatment worked — without it, you are relying on assumption.

Varroa Monitoring Record Sheet: What to Record

Recording your monitoring results consistently makes it much easier to detect trends, compare colonies, and evaluate the effectiveness of treatments over time. A simple paper record or spreadsheet is sufficient.

For each test, record at minimum:

Weather conditions, colony strength, and the presence of any other health issues at the time of testing are also worth noting. These details help you interpret future results in context, especially if you are comparing the same colony across multiple seasons.

Monitor First, Then Make an Informed Decision

Varroa cannot be managed effectively without measuring it. A colony that appears healthy may already carry a mite load that will compromise its winter bees. A treatment applied without a follow-up test may leave the infestation at a level that continues to cause harm.

The three key principles of Varroa monitoring are straightforward:

• Use a sampling method — visual inspection is not enough
• Different methods measure different things and cannot be directly compared
• Interpret your results using the current guidance that applies to your province and the current season

Once you know how to measure Varroa levels in your colonies, the next step is understanding why mite populations can rise again in late fall — even after an earlier treatment worked well.