Varroa mites are a major threat to the health and survival of your honey bees.
In this article, we’ll explain what new beekeepers should know about Varroa including:
- how to monitor infestation levels, and
- your chemical and non-chemical treatment options for managing Varroa as part of an Integrated Pest Management (“IPM”).
Some beekeepers define treatment as any manipulation of the colony to manage Varroa, chemical or not. For our purposes, we are using a narrower meaning: treatment is the use of chemicals whether synthetic or organic.
Varroa Destructor Mites
The aptly named Varroa destructor mite, which appeared in the United States in 1987, is a parasite that attaches itself to the honey bee brood and adult bees.
Varroa mites feed on the host leading to varroosis, a parasitic disease. Varroosis weakens the bee’s immune system making it more susceptible to other diseases and viruses. Varroa aid the spread of disease as they move around the colony.
A female Varroa mite is large enough to be seen by the naked eye at about 1.0 to 1.5 mm across and has eight legs. (To see its legs, you’ll need some magnification.) Reddish-brown in color, they look to me like a darkly rusted pinhead.
Impact Of Varroa Mites On Bee Colonies
Varroa can devastate your honey bee colonies. The Bee Informed Partnership (“BIP”), a not-for-profit organization working to improve understanding of bee health, reported colony losses over 37% in its latest survey. BIP says that as many as 60% of beekeepers report colony losses due to Varroa. The study showed that varroa mites are the “number one concern among beekeepers and a leading contributor to winter colony losses.”
The 2018 NYS Beekeeper Tech Team Report (available here) says that 61% of colonies sampled indicated a mite infestation level that requires “immediate treatment to prevent colony death”. It also says, “Varroa mite levels are a significant predictor of winter loss in New York State.” In the 2016 report, the survey sample indicated 90% of colonies had Varroa. The presence of Varroa is nearly universal among bee colonies.
There is no Varroa in Australia or Antarctica (as of now). If your apiary is in Antarctica, please send pictures!
No magic bullet eradicates Varroa. Most commercial beekeepers use some form of chemical treatment to keep the mites in check because of their potentially dire economic impact; however, a significant percentage of backyard beekeepers report using no treatment.
Note: Other types of mites than Varroa threaten honey bees such as tracheal mites. For our purposes here, all references to mites mean Varroa.
Varroa Mite Life Cycle
A basic understanding of the varroa life cycle helps you understand how an infestation can grow rapidly and overwhelm a colony.
A female varroa mite has two phases in its life cycle: the phoretic phase, where she attaches herself to an adult bee and a reproductive phase within a brood cell.
Phoresis is when an organism attaches itself to a host temporarily for the primary purpose of transportation. Female Varroa mites hitch rides on adult bees to travel within a hive and among colonies.
After a short period, the phoretic mite drops into an uncapped brood cell. Once the cell is capped, the mite attaches herself to the larva and begins to feed and lay eggs. One egg develops into a male mite (for mating purposes) while the rest are females.
When an adult bee emerges from the cell, the adult female mites come out with her to infect other bees or larva. The male mite dies in the brood cell when the nurse bees clean it out.
More mites can reach maturity in drone cells than worker cells because of the more extended development period of drones. Thus, more drone brood likely leads to higher mite counts.
Developing in brood cells means the Varroa population grows in concert with the bee population. With multiple eggs being laid in brood cells the Varroa infestation rate is exponential making it particularly dangerous to the colony.
Weakened by the mite, a bee becomes more susceptible to viruses that may be present in the colony. The mite can also spread these viruses (such as Deformed Wing Virus) as it moves from one host to another.
Mites spread among your colonies as they travel in the phoretic phase between hives on bees that drift among hives or robbers.
Left unchecked, varroa mites and the viruses they spread will eventually cause the colony to collapse. The following video describes the Varroa life cyle:
Monitoring Varroa Mites
The odds are very high that your colonies have some level of Varroa infestation. The purpose of monitoring Varroa is to determine the extent of any infestation. Armed with that knowledge, you can make an informed decision about whether to intervene.
Select a regular monitoring schedule (e.g., monthly). With a large apiary, check at least 10% of your hives for a representative sample. As a beginner with only a few colonies (10 or less), it’s better to monitor a much higher percentage, if not all, of your hives.
You may be able to spot Varroa with a visual inspection of the hive. While this will alert you to their presence, a more precise detection method is needed to determine the extent of the infestation.
You may see phoretic mites on the backs of some bees. However, since mites often attach to the underside of the bee, they may not be plainly visible.
Some Varroa mites fall off bees and plummet to the bottom board. If you’re using a screened bottom board, you can catch them on a pull-out drawer. (These screened boards also help keep small hive beetles and wax moth larva that fall to the bottom from damaging the colony.)
A lot of other things drop to the bottom of the hive so it may be hard to spot the mites. It’s best to look within a couple of days of cleaning off the drawer so that mites are more visible.
Look for spotty brood patterns and particularly, chewed down brood. Chewed down brood occurs when the bees prematurely uncap the brood to remove pupae and larvae along with mites. It could be a sign of high infestation.
If you notice a sudden drop in the bee population, look for Varroa as a possible cause.
The open wounds created by Varroa increase the possibility of viral infections that exist within the colony such as Deformed Wing Virus (DFW). DFW may be apparent in the form of deformed wings or other abnormal deformities and appearances. DFW is a reliable indicator of high Varroa infestation.
The methods described next are designed to provide a more accurate assessment of Varroa levels than just looking through the hive.
Uncapping Drone Brood
An uncapping fork (also called a cappings scratcher) is usually used to uncap cells to extract honey. You can also insert it under the cappings on drone brood at a slightly downward angle to pull the brood out for inspection.
Mites can be clearly visible against the white pupa. For a meaningful count, inspect at least 100 drone cells in a hive selected from different frames. You also look for any Varroa remaining in empty cells.
Generally, a count of 5% or less in the drone brood is considered a low to moderate infestation level. If your count is 20-25%, it’s a heavy infestation and you should consider immediate steps to mitigate it.
The National Bee Unit in the UK has an online Varroa Calculator that you may find useful to assess the results of drone brood uncapping and natural mite drop. Keep in mind that you may need to adjust your input based on your geographic region.
A sticky board is a non-absorbent sheet (preferably white) placed on the bottom board.
Coated with a thin layer of petroleum jelly or shortening (hence, sticky), it traps any mites that drop to the bottom of the hive. A screened bottom combined with a sliding drawer makes inspection easier. If you’re using a solid bottom board, the sticky board should be covered with a screen to keep bees off the “sticky” stuff.
You can make your own or purchase sticky boards from most beekeeping supply companies. Purchased sheets typically have preprinted grid lines to help you keep track of the count.
Arrange your sticky board and leave the hive alone for three days so that any mite drop occurs naturally. After three days, remove the board and count the number of mites. Divide the number of mites by 3 to get an average daily mite drop count.
The size of your hive is an essential factor in assessing a sticky board mite count. A count of 30 – 40 per day for a “standard” hive of 2 deeps and a couple of supers would indicate the need for mitigation.
Alcohol or Soap Wash and Powdered Sugar Roll
Two similar methods of doing a mite count are the alcohol or soap wash and the powdered sugar roll. Besides using different materials to free phoretic mites from bees for counting, the alcohol/soap method kills the bees sampled whereas the powdered sugar roll disturbs the bees but leaves them alive.
(In the course of beekeeping, you’re going to kill some bees by accident during hive inspections. We hate when that happens but have come to accept it. We prefer mite count methods that don’t harm the bees.)
Both methods require that you use about a ½ cup of bees from a brood frame. BE CAREFUL NOT TO TAKE THE QUEEN.
Alcohol or Soap Wash Equipment and Instructions
For this method, you’ll need:
- Standard protective gear, especially a veil, smoker, and hive tool as you would for a hive inspection. This time you’ll be removing some bees for the test.
- One of the following:
- A varroa count double jar (here on Amazon) which includes a mesh lid. )If you’re so inclined, you can make a double jar. Randy Oliver provides instructions at ScientificBeekeping.com. ) OR
- Two mason jars with a solid lid and a mesh lid. You can make a mesh lid or buy one at BettterBee.com OR
- Winter windshield washer fluid (a low-suds soap) or better yet, a 50/50 mixture of 70% isopropyl alcohol and water
- A ½ cup measuring cup OR a jar marked for the ½ cup level to get about the right number of bees (there are an estimated 300 bees in a ½ cup)
- A tub or bucket for collecting the bees. White is preferable as it makes it easier to do one last queen check.
Step 1 – Using your hive tool and smoker, remove a frame of bees and brood from a brood box. INSPECT CAREFULLY TO MAKE SURE THE QUEEN IS NOT ON THE FRAME. If you spot the queen, move her to another frame, or select a different frame and put the queen frame back in the hive. (Seeing the queen will give you great comfort that you have not inadvertently included her in your sample.)
Step 2 – Dislodge the bees from the frame into your bee collection container. With the container on a solid surface, you can give it a good thump to drop the bees. Some of the bees will fly off back to the hive, and that’s okay. Take one more look for the queen if you haven’t seen her yet.
Step 3 – With your measuring cup, scoop a ½ cup of bees and put them into the jar.
Step 4 – Pour enough alcohol mix or washer fluid into the jar about halfway or enough to cover the bees.
Step 5 – Close the jar and shake vigorously for about a minute to dislodge mites from the bees.
Step 6 – Using the mesh cover, drain the liquid into the other jar separating the bees from the wash and dislodged mites.
Step 7 – Look at the bottom of the jar and count the mites that have settled in the liquid.
Step 8 – Divide the number of mites counted by 300 (the estimated number of bees in a ½ cup) to the percentage of bees affected. For example, 6 mites ÷ 300 bees = .02 = 2%. See information below on assessing the mite count.
Sugar Roll Equipment and Instructions
As we mentioned, the sugar roll is like the alcohol/soap wash, except it doesn’t kill the bees. Much of the equipment needed is similar:
- Standard protective gear, especially a veil, smoker, and hive tool as you would for a hive inspection so you can remove bees.
- A jar with a mesh lid
- Powdered sugar
- Misting bottle with water
- Tub or bucket (preferably white) to collect bees off a frame
- A white plate for collecting sugar and mites after the roll. You may be able to use the tub/bucket, but it may still have bees in it when you’re at the mite counting step.
Follow Steps 1 – 4 from the alcohol wash method above to collect bees in your jar. The mesh lid will keep the bees in.
Step 5 -- Put enough powdered sugar in the jar to coat the bees – about a few tablespoons.
Step 6 – Shake and roll the jar vigorously to coat the bees thoroughly and dislodge the mites.
Step 7 – Let the jar sit for about 3 – 5 minutes. DO NOT SKIP THIS STEP. It will improve the mite fall resulting in a more accurate count.
Step 8 – Shake the powdered sugar and mites through the mesh lid onto your white plate.
Step 9 – Using the mister, dissolve the powdered sugar. The reddish-brown mites will become visible against the white plate.
Step 10 -- Count the mites.
Step 11 – Divide the number of mites counted by 300 (the estimated number of bees in a ½ cup) to the percentage of bees affected. For example, 6 mites ÷ 300 bees = .02 = 2%. See information below on assessing the mite count.
Step 12 – Return the sampled bees to the hive. Their mates will clean the powdered sugar off them.
This video from the Honey Bee Health Coalition demonstrates both the alcohol wash and sugar roll sampling methods:
Assessing Mite Counts
Keep in mind that, with these methods, the mite count only estimates the percentage of bees with phoretic mites. The higher this count, the higher you can expect the mite count to be in the brood. Some suggest doubling the mite count from the wash or sugar roll.
So how many mites are too many? Researching the topic of acceptable thresholds indicates there is no one-size-fits-all answer.
Honey Bee Health Coalition has an online Varroa Management Decision Tool here to help you decide. By answering some questions, you can find what’s considered an acceptable threshold depending on the colony’s phase. If your levels are acceptable, the tool provides preventative actions. If levels are above acceptable limits, seriously consider treatment.
Generally, a mite count of 1% -- 2% is acceptable. Mite counts between 2% and 3% suggest that you may want to take steps before the situation worsens. Greater than 3% indicates a high risk to your colony. This information provided in Honey Bee Health Coalition’s Guide to Effective Varroa Sampling & Control is downloadable here.
Talk to other beekeepers in your area. Find out how they are dealing with Varroa and what their experience has been with different levels of infestation.
Determine the progression of varroa growth in your colonies with periodic monitoring using a consistent method. Identifying the trend will give you a better handle on the risk to your colonies.
If you Google around the internet, you’ll find a debate between proponents of actively controlling mite populations with various forms of treatment (particularly, chemical treatment) and those that believe in treatment free alternatives as being more natural and beneficial in the long run.
Even if you opt to treat for mites, many of the procedures used by treatment free beekeepers can help keep your mite count down and reduce your need to use chemical intervention. You can incorporate both into an Integrated Pest Management program.
Varroa Treatment Options
If you opt to chemically treat your hives, you can choose between synthetic or natural pesticides designed to primarily target the mites, not the bees. They are often referred to as miticides.
Synthetic miticides are man-made compounds not ordinarily found in nature; natural ones use organic acids or essential oils.
Do not be lulled into a false sense of safety by the word “natural”. Some of these materials can be harmful if not used properly. For example, oxalic acid, while a naturally occurring substance, can be very harmful if you inhale the vapors. Use caution with all these products.
Varroa Mite Treatment Comparison
Common varroa mite treatments are compared in the table below. The information is intended as a general guideline. CAREFULLY READ ALL INSTRUCTIONS AND WARNINGS INCLUDED WITH EACH PRODUCT, ESPECIALLY REGARDING THE USE OF PROTECTIVE EQUIPMENT.
|Name||Active Ingredients||When to use||General Application Info||Length of Treatment||Temperature Restriction||Use during honey flow?|
|Apistan®||Fluvalinate||Spring and autumn||Strips hung in the brood chamber. Bees contact and transfer active ingredient.||6 weeks||None but bees should not be dormant.||No. Can add honey supers 2 weeks after treatment.|
|Apivar®||Amitraz||Spring and autumn||Strips hung in the brood chamber. Bees contact and transfer active ingredient.||42 - 56 days, not longer||None but bees should not be dormant.||No. Can add honey supers 2 weeks after treatment.|
|CheckMite+®||Coumaphos||Spring and autumn||Strips hung in the brood chamber. Bees contact and transfer active ingredient.||42 to 45 days, not longer||None but bees should not be dormant.||No. Can add honey supers 2 weeks after treatment.|
|ApiLife Var®||Thymol, eucalyptys oil, L-menthol||Early spring and after honey harvest||Tablet broken in 4 pieces, each place on top bars at the edge of the brood nest to fumigate the hive.||3 consecutive applications: 1st - 7 to 10 days; 2nd - 7 to 10 days; 3rd - 12 days||Between 64° and 95° F (18° and 35° C).||No. Add honey supers 30 days after treatment.|
|ApiGuard®||Thymol||Spring and autumn||Place open tray (which may require a spacer) in the hive to expose thymol gel. Bees contact gel and carry it through the hive.||2 consecutive treatments: 1st - 10 to days; 2nd - 2 to 4 weeks||Between 60° and 105°F (15° and 40°C). Avoid during nectar flows.||No. Manufacturer website is silent. Some forums indicate waiting 2 weeks.|
|Formic Pro®||Formic acid||Spring and autumn||Strips placed on top bars in brood boxes fumigate the hive with formic acid.||2 options: 14 day or 20 day||Between 50° and 85° F (10° and 29° C).||Yes.|
|Hop Guard II®||Hop compounds||Any time of year but best with less brood present||Hang strips over brood frame top bar so it hangs between frames.||30 days||Between 52° and 92° F (11° and 33° C).||Yes. Don't harvest wax and honey from brood boxes.|
|MiteAway Quick Strips®||Formic acid||Spring and autumn||Strips placed on top bars in brood boxes fumigate the hive with formic acid.||7 or 21 day treatment options||Between 50° and 85° F (10° and 29° C).||Yes.|
|Oxalic Acid||Oxalic acid dehydrate||Anytime there is no capped brood as it does not kill mites in cells||2 methods of treatment: dribble method mix of oxalic acid and light sugar syrup OR fumigation with a vaporizer.||3 consecutive weekly treatments recommeded||Between 35° and 55° F (2° and 13° C).||No.|
NOTE: Product names link to the manufacturer’s or distributor’s website for more detailed information except for oxalic acid (a generic product) which links to a video from the Honey Bee Health Coalition.
As we mentioned, follow all safety instructions for any miticide which may include, among other things:
- Wear chemical or acid resistant gloves
- Use protective eye gear
- Avoid inhaling fumes (best done by wearing a mask approved for your application)
- Avoid contact with your eyes, skin or clothing
- Wash up thoroughly after using miticides
- Store and dispose of any chemicals properly.
Oxalic acid vaporizers get extremely hot with temperatures well above 300°F (148.8°C). Beeswax and the wooden frames in your hive are both flammable. Check to make sure your vaporizer is not touching any burr comb or frame. You may want to consider a vaporizer that keeps the heat outside the hive (such as the ProVap 110 available here on Amazon). Vaporizers are expensive; you may want to skip them all together and apply oxalic acid via the “dribble method” which is covered in this Honey Bee Health Coalition video.
Check whether a product is approved for use at your location. For example, as of this writing:
- ApiLife Var is not registered in CA, AK, and DC per the Veto-pharma website.
- California requires a Grower’s ID issued by the Agriculture Commissioner for Apiguard according to one supplier.
You may see the names oxalic acid and formic acid and wonder “what the heck is ‘natural’ about that?”
- Oxalic acid (also called wood bleach…WHAT??) is an organic compound that occurs naturally in many foods including spinach, broccoli, cucumbers, brussel sprouts, and rhubarb. (Though mom never told me to finish my oxalic acid before I left the dinner table.)
- According to Wikipedia, formic acid “occurs naturally, most notably in ants” and “is a naturally occurring component of the atmosphere primarily due to forest emissions.” In addition to killing varroa mites, it eliminates tracheal mites, another honey bee pest.
In choosing any of the products, familiarize yourself with the drawbacks associated with them.
- All the synthetic miticides leave some amount of residue in honey and wax. Do not use them during honey flow with supers on. In some cases, it will dissipate over time.
- Treatments can have some negative impact on the bees, including impaired queen reproduction and increased mortality. The risk of these issues tends to be more significant when using treatments at temperatures above the recommended limit.
- Both Apistan® and CheckMite+® are not recommended in New York due to “adverse effects to bees, persistent residues in wax, and mite resistance.” See Varroa Mites: A Guide to Control Methods in New York here.
When purchasing treatments, be aware of how much you’ll need to treat your apiary. Order too little and you may not adequately address your mite issue. Over order and you might end up with product that you can’t use before its expiration date.
It’s good practice to vary your treatment options so as not to induce mite resistance over time.
Combine treatment free practices described below with your treatment options as part of an Integrated Pest Management plan. Minimizing the mite count with these cultural methods may reduce the need for miticides. That’s a good thing!
Varroa Treatment Free Options
Some beekeepers may have a strict definition of “treatment free” that includes any manipulation of the hive. For our purposes here, we are using a more limited meaning. “Treatment” refers only to the use of chemicals and compounds, whether synthetic or natural, like those described above. “Treatment free” refers to things you can do without chemicals.
Use Screened Bottom Boards
Instead of a solid bottom board, use a screened bottom board. Varroa (and other pests such as small hive beetles and wax moth larva) that drop from the hive are unable to crawl back up or attach themselves to bees.
Screened bottom boards do not have a significant impact on mite counts but may provide marginal help.
Adding an easily accessible sticky board helps in monitoring Varroa.
Drone Brood Management
Varroa reproduce more in drone cells because of the more extended development period. Many beekeepers remove capped drone cells to lower the mite count in the hive. You can cut out and dispose of many capped drone cells or use drone frames as a trap.
Plastic drone frames (usually green for easy identification) are available from most bee supply companies. These frames are embossed with large cell configurations inducing the bees to build drone cells for the queen.
Once the drone cells are capped, remove the drone frame, and place it in the freezer for a day or so. Freezing will kill the larvae and any mites. Return the frame to the hive, and the bees will clean them out. The cells can then be reused to trap more drone brood.
You can follow Randy Oliver’s design at ScientificBeekeeping.com and build your drone frames (the Oliver Trap Frame) to achieve the same results. This frame provides a small section of foundation at the top for honey storage. The lower part is a foundationless section and usually ends up with drone brood.
Be careful not to let the drone brood emerge (along with the mites). Freeze it first!
Breaking the brood cycle eliminates brood cells for a while, giving the mites no place to reproduce. Combined with average mite drop and bee grooming of phoretic mites, the growth of the mite population is arrested.
You can remove the queen from the hive and cage her temporarily or move her to another box with some attendant bees. Reunite the queen with the colony after about a week. Having limited her egg laying will break the brood cycle.
An alternative is to replace the queen with a new one, preferably from Varroa resistant stock, which not only breaks the brood cycle but can improve the genetic makeup of the colony.
Swarming is a natural bee behavior. The queen leaves the colony with a lot of workers and establishes a new colony elsewhere. Bees left behind raise a new queen with the eggs and brood in the original hive.
The new colony will be without brood in their new home while the bees build out comb for egg laying. Without brood cells, there will be no new varroa for a while.
In the old colony, the brood cycle is interrupted until a new queen can be raised, mated, and begin laying eggs.
Beekeepers achieve similar effects with an artificial swarm (a type of hive split). If you’re a new beekeeper, you’ll need extra hive equipment to accomplish this.
The best time to split is during a colony’s spring population increase. Do this only with healthy colonies and in time for both groups to build up for the winter
Ideally, you’ll have queen cells for the bees to raise a queen. If not, you can introduce a mated queen to the moved hive.
This step can also prevent a colony from swarming (and losing half your bees) and has the added bonus of giving you an inexpensive new colony.
One of our hives swarmed this year, but we were fortunate enough to recapture them and create a new colony. It was like getting a free bee package!
Varroa Resistant Bees
Consider getting mite resistant bees or introducing a mite resistant queen to change your colonies genetic makeup.
According to a study at NC State, Russian bees are more resistant to Varroa than Italian honey bees.
Breeders have been developing Varroa Sensitive Hygiene (VSH) bees that can be bred into any race. These bees exhibit behavior that helps control the mite population. They will pull out infested brood preventing mites from maturing.
The American Association for the Advancement of Science has an interesting article about breeding varroa-resistant bees:
This year we got a package of Saskatraz bees developed by The Saskatraz Hybrid Project. According to their website, Saskatraz stock is bred for honey production, wintering ability, and resistance to mites and brood diseases. We’ll see how it goes.
Powdered Sugar Dusting
Some beekeepers dust the bees with powdered sugar. Sugar collects on the bees causing mites to drop. Bees also remove sugar from each other and, in the process, dislodge Varroa.
Technically, I guess this is a form of treatment, but it involves no chemicals and doesn’t harm the bees.
Bee Gym (Really?)
UK-based Vita Bee Health makes a chemical-free varroa grooming aid called the Bee Gym explained on their website. In theory, bees knock off mites by rubbing on various parts of the device.
I have no idea if it works, but if you’re serious about treatment free beekeeping, it may be worth trying.
Limit Robbing and Drifting
Varroa mites can hitch a ride into one of your colonies on a robber or drifting bee.
To minimize drifting, vary the angle/direction of hive openings if you have space. Bees are great navigators but can easily slide into a neighboring hive in error.
Even without the risk of varroa infestation, you should protect your hives’ general safety with robbing prevention. Our article on Summer Nectar Dearth provides details on robbing prevention.
Doing all these tests for Varroa will be meaningless if you don’t track the data. Record the timing and results of all your sampling and treatments for future reference. It’s the only way to monitor how your hives are doing.
See our article Record Keeping For Beekeepers
(A Guide To Why, What & How) for more information.
Varroa mite infestation is a serious threat to the health and viability of your colonies. Take the time to learn as much as you can to make informed choices.