If you’re a beekeeper in Australia, then you can disregard this guide. For the rest of us, managing varroa mites is an ongoing battle that gets easier with experience.
There is no “one size fits all” approach to varroa mite treatments and each option has its limitations. More importantly, using a variety of ways to treat varroa mites is essential for avoiding resistance.
Quick facts you need to know
- Varroa mites are a serious threat to the honey bee around the world.
- Varroa mites prefer reproducing in drone brood cells.
- The mites may avoid chemical treatments by reproducing under capped brood.
- Controlling the mite population reduces the spread of viruses.
- Regular testing for varroa mites will allow beekeepers to act quickly once these parasites reach an unacceptable level.
- Treating varroa in the fall is a crucial part of overwintering survival.
How to treat varroa mites
Treatment approaches may be preventative in nature like buying resistant bees and using small cell comb. If mite numbers breach an unacceptable threshold, beekeepers can use non-chemical strategies like brood break and mite trapping or they can apply soft and hard chemicals.
Using a combination of two or more methods will improve efficacy and reduce varroa mite resistance.
1. Preventative strategies
A preventative approach to varroa mite control is focused on reducing pest reproduction. Common methods include utilizing mite-resistant bees and adding small cell comb.
Mite resistant bees
Researchers have successfully developed various bee stocks that have some resistance to varroa mites. When beekeepers choose to use mite-resistant bees it reduces the need for chemical treatments.
Varroa Sensitive Hygiene (VSH) bees can recognize when mites are present and they understand the severity of this invasion. VSH bees will quickly remove pupae from the hive that are infested with varroa mites. This contributes to a more hygienic hive and helps manage the mite population.
Ankle biters have been bred to encourage the trait of biting mites and dislodging them. Studies have found these honey bees had better overwintering success than other strains of bees, even without additional varroa treatments.
Scientists have also found that Russian bees experience slower varroa mite population growth compared to other types of bees. The percentage of their brood that becomes infested is lower, making them a good choice for beekeepers in varroa mites are a problem.
Small cell comb
Since the 1950s, the beekeeping industry has experimented with different-sized hexagonal foundations for honey bees. While wild bees build comb that has 4.9mm hexagonal cells, commercial comb was made using 5.4mm cells. This resulted in larger bees and more honey.
The disadvantage of larger cells is more space for varroa mites to reproduce. This has led researchers to consider decreasing the cell size to shorten the post-capping period. Whether this tactic results in the reproduction of fewer mites per cell is debatable.
Although the evidence isn’t conclusive that small cell comb reduces mite numbers, using this equipment won’t harm your bees.
2. Non-chemical strategies
Once varroa mites are discovered in the hive, the beekeeper may decide it’s time to act. If the use of chemicals doesn’t sit well with your philosophy, then try one of the following ideas. They don’t pack the same punch as commercial varroa mite treatments, but they will still get results.
A brood break will significantly reduce the amount of brood in the colony. It is a useful way to limit the number of protective homes for the mites to reproduce in.
Brood breaks can be accomplished by removing or caging the queen for around three weeks. A push in cage is a good option, restricting the queen to laying in a very small area of the hive. These cages are roughly four square inches and allow worker bees to attend to her.
After three weeks of restricting egg production, all the existing brood will hatch, forcing the mites out of their cells and onto adult bees. With no brood in the hive, honey bees increase their grooming behavior. Adding a screened bottom board during this period will help decrease mite numbers.
A brood break is an excellent strategy to implement during a dearth period to help ease the stress of reduced food sources.
Varroa mites prefer reproducing in drone brood, thanks to the extended post-capping period. The mites found under drone cappings are six times that of worker cappings!
Beekeepers can use this knowledge to their advantage by adding extra drone brood to the hive as a trap. Before the young drones emerge from their cells, the brood can be removed, along with the developing varroa mites.
After freezing the brood and killing off the mites, it can then be returned to the colony. Instead of freezing the frames, another option is to scrape the brood off and then return the clean frame.
Mite trapping is often not effective enough to use as a treatment on its own. However, it is great combined with other chemical treatments.
Screened bottom board
As bees groom themselves and move about the colony, it’s natural for varroa mites to sometimes fall off. In a regular hive with a wooden bottom, they’ll climb back onto their host.
Adding a screened bottom board will greatly reduce the number of mites re-attaching themselves to bees. They also decrease brood cell mite invasion which is good news for the hive.
Beekeepers who add a board will still find that varroa mites eventually reach their population threshold. To keep a colony healthy long-term, other control techniques should be used in conjunction with a board.
A sprinkle of powdered sugar over honey bees is an effective mite control technique. It encourages each bee to groom itself, resulting in mites dropping to the bottom of the hive. A strategically placed screened bottom board will pair well with this option.
While powdered sugar is a low-cost, non-intrusive way to weed out unwanted mites, it isn’t usually enough to eradicate the parasites. You may want to consider using chemicals as well, which we’ll look at next.
3. Soft chemical strategies
Soft chemicals are manufactured using natural ingredients and are a good midpoint between harsh chemicals and non-chemical approaches. Their application is recommended before resorting to hard chemicals.
Essential oils, organic acids, and hop beta acids all fall into the soft chemical category. These naturally derived products won’t leave residues in the hive’s wax and other products.
Keep in mind that any chemical should only be used when absolutely necessary. Even soft chemicals should only be resorted to when your inspections indicate it is necessary.
Oxalic acid comes from plants like kale, rhubarb, and spinach. It is a natural chemical that works well at controlling mites out in the open and attached to bees.
Whether you use a dribble or vaporizing oxalic acid, it won’t penetrate the brood cappings. That makes it a good candidate for controlling varroa in winter or early spring.
Oxalic acid isn’t a perfect solution and overuse can have negative effects on the colony. This could include decreased worker bee activity and a reduced life expectancy. Another pitfall of using this acid in high doses is that it can reduce the size of the brood area and increase larval mortality.
Beekeepers should never rely on oxalic acid as a standalone treatment. Instead, use it in conjunction with other strategies on this page.
Formic acid is derived from honey and is another natural weapon against varroa mites. It has an advantage over oxalic acid as it can penetrate wax cappings when highly concentrated. This means reproducing mites are fair game using this acid, which is a huge bonus.
One of the biggest challenges for beekeepers using formic acid is making sure the temperature is appropriate. The recommended range for use is 50-85°F. Hot weather has the potential for queen loss or increased brood mortality; cooler temperatures reduce the efficacy of the treatment.
Hops beta acids
Hops beta acids come from the hops plant and can be used to help reduce varroa mite infestations. It is best used where brood is limited as this acid won’t penetrate cappings.
This treatment can be applied any time of year even during extremes of temperature and through honey flow. However, beekeepers should keep in mind that the efficacy of hops beta acids will vary. Other treatments like formic and oxalic acid are generally more effective.
Beekeepers searching for an essential oil solution can try thymol which comes from the thymol plant. Its vapors are distributed through the hive thanks to bee activity.
As the treatment proceeds, worker bees will empty cells near the treatment zone. When applied in spring, the area of brood may be reduced.
There’s a delicate balancing act with this solution. The vapors must be concentrated enough in the hive to kill the varroa mites, but not so high that the bees are harmed.
Thymol is most effective when the temperature is between 68-77°F. We suggest avoiding this treatment when temperatures are expected to fall below 54°F.
Like all treatments, thymol has its disadvantages. Studies have found that thymol may have adverse effects on colonies and especially on larva. Source.
Thymol also lacks the strength to penetrate cell cappings. That means it won’t control varroa mites protected within brood cells.
Finally, thymol may result in an aggressive colony and induce robbing behavior.
4. Hard Chemical strategies
As the fall arrives, beekeepers may face large infestations of varroa mite in their hives. To give your colony the best chance of successfully overwintering, an application of hard chemicals like miticide or acaricide before the winter bees arrive is your best bet.
Hard chemicals will generally kill up to 95% of the varroa mite population. However, synthetic chemicals can harm bees and make them more susceptible to nosema disease. Resistance to these treatments is also a major concern.
The application of synthetic chemicals is best used as a last resort in integrated pest management (IPM).
Amitraz is the most popular synthetic acaricide on the market. It has a 99% efficiency rate against mites in honey bee colonies. Two commercial products that contain Amitraz are Apivar and Apitraz.
Apivar application is straightforward, requiring strips to be placed in brood boxes. Amitraz gets released and transported around the hive when the bees touch the strips.
The strips should be left in the hive for six weeks. During this time, Amitraz is continuously released, causing excitation and then paralysis of the mites. They fall from the backs of the hosts and can’t get back on.
Beekeepers should never use Amitraz during honey flow. Once treatment is completed, wait 2 weeks before adding a super.
Apistan is another hard chemical that kills mites by exciting their nervous system to exhaustion. It can be applied any time through the year, but it is most effective after honey flow in late summer.
Two polymer strips are hung vertically between frames in the brood box. They contain fluvalinate which gets transferred through the hive by bee activity.
Apistan should never be used during a honey flow. After 6-8 weeks of treatment, supers can be replaced immediately.
When should I treat varroa mites?
Beekeepers may decide to treat varroa mites at regular intervals based on the calendar method. That could mean treating the colony every three months, whether mites are spotted or not.
Other beekeepers may prefer testing the hive and treating it once a threshold is reached. For example, when the mean abundance of 2 mites per 100 bees is reached, treatment may be required.
We recently polled a group of 240 beekeepers and discovered that 80% used a combination of calendar and mite count.
How do I test for mite resistance to chemicals?
If your hive has a significant population of mites, place an Apistan strip (or similar treatment) in the brood box. Wait 24 hours then check the mite drop rate. If the count is in the hundreds, then you can assume the active ingredient is doing its job.
Can I treat for varroa mite with honey supers present?
Most commercially sold varroa mite treatments aren’t suitable for applying when honey supers are in. However, formic acid won’t have any negative effect on your honey supers and can be used year-round.
Summary of chemical treatments for varroa mites
|Treatment||Description||How to apply||Treatment duration||Temperature restricted?||Can use during honey flow?||When to use|
|Apistan||Contact based treatment using Fluvalinate as active ingredient||Hang strips in the brood box||6 weeks||No. Bees should be active.||No. Supers can be added immediately after treatment concludes||In the fall and spring|
|Apivar||Contact based treatment using Amitraz as active ingredient||Hang strips in the brood box||6 weeks||No. Bees should be active.||No. Supers can be added 2 weeks after treatment concludes||In the fall and spring|
|CheckMite +||Contact based treatment using Coumaphos as active ingredient||Hang strips in the brood box||42-45 days||No. Bees should be active.||No. Supers can be added 2 weeks after treatment concludes||In the fall and spring|
|Formic Pro||Fumigant based treatment using Coumaphos as active ingredient||Strips laid on top bars in brood box||1 strip for 10 days or 2 strips for 14 days||Must be 50-84°F during daytime||Yes||In the fall and spring|
|HopGuard II||Contact based treatment using beta acids and hop compounds as active ingredients||Hang strips in the brood box||14 days||Avoid using below 50°F if possible||Yes||Year-round, best with minimal brood|
|HopGuard 3||Contact based treatment using beta acids and hop compounds as active ingredients||Hang strips in the brood box||14 days||Avoid using below 50°F if possible||Yes||Year-round, best with minimal brood|
|MiteAway Quick Strips||Fumigant based treatment using formic acid as active ingredient||Strips laid on top bars in brood box||10 days or 14 days||Must be 50-84°F during daytime||Yes||In the fall and spring|
|Oxalic acid (dribble)||Contact based treatment using oxalic acid as active ingredient||Apply directly to bees using a syringe||1 treatment each week for 3 weeks||35-55°F when bees are in a loose cluster||No||The fall or early spring with little or no brood.|
|Oxalic acid (vaporizer)||Fumigant based treatment using oxalic acid as active ingredient||Fumigate using a vaporizer||1 treatment each week for 3 weeks||35-55°F when bees are in a loose cluster||No||The fall or early spring with little or no brood.|
To effectively deal with varroa mites (Varroa destructor), the beekeeper should employ a combination of mite population management strategies. There are many options to control varroa mite populations, including preventative, non-chemical, soft chemical, and hard chemical treatments. No choice is perfect so beekeepers should weigh up the advantages and disadvantages of each before proceeding.
We encourage beekeepers to initially focus on managing varroa mite numbers without using hard chemicals. If nothing is keeping the numbers down, then look at commercial chemicals as a final resort.
As the seasons pass, continue to rotate treatments to improve your odds of success and to improve the wellbeing of your honey bees.
Once you have your varroa mite population under control, you want to think about other potential threats. Check out our guide to keeping ants out of the hive to help protect your colony from another pest which no beekeeper wants in their hives.