How to Check for Varroa Mites

Field and Laboratory Tests for Mite Levels

Varroa mite checks can be simple, like the sugar shake and alcohol wash methods, or more intensive microscopic analysis. If the goal is to monitor Varroa mites for routine surveillance and treatment, then alcohol washing half a cup of bees (~300 adults) is sufficient. If the goal is more a complex differentiation between honey bee diseases, then laboratory testing by your local state department is more ideal.

Selecting Bees for an Alcohol Wash

Equipment required:

• Jar with a screened/mesh lid,
• Measuring cup/scoop,
  • Optional plastic tub to make scooping the bees easier.
• Alcohol of choice (methlyated spirits or rubbing alcohol),
• Cheesecloth (or similar) and container underneath to capture the mites/alcohol respectively.
  • Alternatively, commercial testing kits like the Veto-pharma EasyCheck tool can be used.

Now, open the hive and:

1. Select a brood frame containing nurse bees. Ensure the queen is not on the frame.
2. Shake the bees onto the ground (or plastic tub).
3. Scoop half a cup, ~300 adult bees, into the jar & add alcohol (if you haven’t already done so).
4. Seal the jar and shake/swirl to mix and dislodge the mites.
5. Pour the contents onto the cheesecloth and check for any mites caught in the cloth.

Selecting Bees for a Sugar Shake Test

Similar to the alcohol wash, you will need:

• Jar with a screened/mesh lid,
• Measuring cup/scoop (optional tray for dumping bees, as above),
• Icing/baking sugar – not regular granulated sugar,
  • The fine flakes of the icing sugar are more likely to stick onto the mites.
• Bowl of water or white paper for dumping the bees.

Now, open the hive and:

1. Select a brood frame containing nurse bees. Ensure the queen is not on the frame.
2. Shake the bees onto the ground (or plastic tub).
3. Scoop half a cup, ~300 adult bees, into the jar & add sugar (if you haven’t already done so).
4. Seal the jar and shake/swirl to mix the contents and dislodge the mites.
5. Pour the jar contents through the mesh onto the paper or waterbowl and check for mites.
   1. On paper, they would appear as a red-brown contrast against the white background.
   2. In water, they would float up to the surface while the sugar sinks.

Brood Rearing Phase and Mite Risks

The table below, adapted from the 2022 publication by the Honey Bee Health Coalition, proposes treatment threshold for mite populations based on the season and number of mites found. It forms the basis of the method presented below in calculating Varroa levels, and is a handy field guide for many beekeepers.

Determining Mite Treatment Thresholds

Whether your colonies require chemical treatments for Varroa mites is dependent on the season and brood rearing phase (table above). Assuming 300 bees are used in the field tests, the formula for mite load is:

Number of Mites / Number of Bees * 100

For example: it is Spring and the alcohol wash method of 300 bees found 7 mites. Putting into the formula above we have 7 mites / 300 bees * 100, which results in a mite load of 2.3%. Based on the table above, it would fall under the “Control Immediately” category to reduce the risk of severe infestations for the remaining season. Chemical treatments include oxalic acid and Flumethrin for controlling Varroa.

Keeping Track of Mite Counts

Add it to your logbook, you are writing notes after every inspection, right?

Monitor regularly. Some states may require you to submit alcohol wash results every few months as an indicator of your hives’ health. Log your data, mite counts and general observations. The counts could be used to make a graph of Varroa populations over time, and would look quite fetching. Likewise with treatments, consider conducting a mite test before and after application to gauge effectiveness.

Many ways to track, so long as you do it consistently.

Other Methods for Varroa Mite Checks

The 2022 publication by the Honey Bee Health Coalition evaluated a number of alternative field tests for Varroa mites, and explained why they are not as reliable. This list is not exhaustive, and if you know of other suggestions, do let me know.

Carbon Dioxide Injections

Carbon dioxide injections can be done in the aforementioned Veto-pharma EasyCheck tool with a bicycle tyre inflator. This method introduces low-pressure CO₂ into the closed system, knocking both bees and mites unconscious. The anesthetized mites detach from the bees and fall to the bottom of the container.

Bava and colleagues (2022) tested CO₂ injections against the sugar shake test, and found the latter to be more effective: CO₂ testing resulted in a greatly underestimated mite count when compared to the sugar shake. Additionally, incorrect use of the CO₂ test resulted in cold burns on the bee’s body, with prolonged exposure resulting in further deteriorations to the bee’s health. The authors suggest sugar shaking in place of CO₂ testing.

Ether Rolls, or Engine Starter Fluid

The reader can draw immediate conclusions about the safety of this method. Like the alcohol wash, this procedure kills bees but is less commonly used. Around 300 adult bees are placed into a clear jar with a sealed lid, and several sprays of ether are applied. The jar is shaken for a minute to let the ether mix with the bees. Eventually, mites stick to the sides of jar and can be counted.

Issues around this method are range from having mites being obscured by the bees inside the jar, to the environmental toxicity of ether and its flammability risks. Less reliable, yet just as lethal as the alcohol wash. Perhaps can be used as a last resort? For a visual on how this method is done, refer to this video.

Drone Brood Assessment

Since Varroa reproduces inside capped brood, uncapping sealed cells is a method for estimating (or rather, eliminating) mite populations from a colony. Mites have a preference for drone cells over workers, due to a longer larval period prior to capping (~9.5 days), and longer developmental time (24 from egg laying; Charriere et al., 2003). Coupled with their larger size, this gives mites more time and resources for reproduction inside the comb. That being said, in moderate-to-high infestation levels, the worker brood will also contain mites.

Enter the drone uncapper. In colonies with a suspected infestation, uncap the drone comb and note any mites that emerge. This method is unreliable for determing the colony mite count, even if you politely ask mites to distribute themselves equally across drone cells. Immature mites are white/translucent in colour and are difficult to see.

Drone uncapping has its place in in integrated pest management and is known as “drone trapping”:

1. Identify drone comb, and monitor it until most cells are capped.
2. Removed the capped comb (replacing the frames removed), and freeze it for 2-3 days to kill mites (and drones).
3. Return the now-thawed frames back to the hive. Repeat every 24 days (the length of a drone brood cycle).

Visual Varroa Inspections

Unless the reader plans on counting 300 individual bees, this method is only an indicator on the extent of infestations. If you find mites on adults, it is a solid indicator of a severe infestation, and management should promptly commence to prevent colony collapse and mite dispersal.

Sticky Board Debris Sampling

Sticky boards check mite populations based on the number of mites that fall from the hive in a given time period. It would serve as a good indicator of the “daily mite drop”, yet reliable results are difficult to obtain due to factors like ants and scavengers, who frequent the bottom board for hive debris. In some places like Germany, beekeepers who have a mite count greater than ten mites a day are told their hives are “severe infestationly” (reviewed in Conte et al., 2010), and should treat accordingly. However as with the visual inspections, the variations are too great for it to be reliable- some days may have twelve mites fall. Others, one or none.

Reporting Varroa data

At the time of publication in 2023, it was mandatory to report alcohol wash results in Australia no matter the outcome. As part of the government plan to monitor Varroa mites, the results help map the overall bee colony health in a given region. Researchers use this data to study infestation patterns, monitor treatment effectiveness, and assess the impacts on bee health. By understanding the pathologies of Varroa, we can (theoretically) develop better management techniques and policies… Like covid, manadatory things come and go, and now we just carry on managing Varroa to the best of our ability. Funny how things turn out

All up, bees are an important agricultural resource, and maintaining healthy populations is vital for food security. For those who would rather help native bees over Apis mellifera, then there are other methods available in the aforementioned article.

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