Varroa mite management in the hive is a topic relevant to all beekeepers, and there is a wealth of information available online and in beekeeping books. This article is intended only as a brief overview of various methods used to deal with varroa mites in your hive.
Varroa mites are a parasitic pest of the honeybee, discovered in the early 1900’s in Asia and appearing in the United States in 1987. Since its introduction into the European honeybee population, the varroa destructor mite has become the most serious pest the hives have to contend with. Varroa mites attach themselves to the bee (larvae and adult) and feed off their bodily fluids. In the process they serve as a vector for a variety of viruses that further weaken and can eventually kill a colony.
A common mistake of beginning beekeepers is to assume if you don’t see mites on your adult bees then you don’t have any mites in the hive. Mites are nearly impossible to spot on a moving bee, but there are several methods to check your hive’s mite levels.
- Alcohol Wash: The alcohol wash is the most accurate method for detecting mites. Take a 1/2 cup of bees (approximately 300 bees) from the brood nest. Don’t get the queen! Place the bees in a cup and cover them with rubbing alcohol, swish thoroughly, and then pour through a screen with holes large enough to allow the mites to fall through and small enough to leave the bees behind. It works best to pour into a clear container. Count the number of mites dislodged from the bees and divide by 3. This will give you the rate of infection per 100 bees. Example: 12 mites divided by 3 equals 4 mites per 100 bees, or a 4% infestation. This method does kill the bees.
- Sugar Roll: The sugar roll is similar to the alcohol wash, but use powdered sugar instead of rubbing alcohol. If you shake the sugar and dislodged mites through the screen and into a bowl of water, the sugar will dissolve and you can easily see the mites. This method is slightly less accurate than the alcohol wash, but it does not kill the bees.
- Sticky Boards: A Vaseline or vegetable oil covered piece of cardboard is placed under a screened bottom board or on top of a solid bottom board. The sticky board is removed at a later time to count the number of mites that have fallen and gotten stuck. They are generally counted at 24 hours and again at 2-3 days. This is the least accurate method of counting mites, but will definitely let you know if you have a severe infestation.
- Drone Brood Sampling: Open 50 drone cells in various areas of the hive. Double the number of infested cells and that will give you the % of infected brood cells in the hive. This method is not very accurate and can only be done with there are ample drone brood cells.
Each of these sampling methods will give you a final numerical result. To properly interpret your results you need to compare your infestation rates. You can compare your rates before and after treatment to make sure the treatment was effective. You can compare one hive to another, or one yard to another, to help you determine which hives are managing mites well on their own. Compare this month’s results to last month’s to find out if your problem is getting worse or if the bees are coexisting with the mites without being overrun. Compare your rates to other beekeepers in the area and ask at what threshold they begin treating their hives. Remember to compare apples to apples! Only compare your results to others from the same sampling method, as each method varies in how effective they count the actual mites.
Now that you know your mite infestation rates, it’s time to choose a management method. Beekeeping approaches to mites range from a hands off, let the bees sink or swim on their own style all the way to a scorched earth, use all available chemicals all the time approach. It’s up to you do chose the beekeeping style that suits your goals and personal worldview.
- Manage with genetics-purchase varroa resistant queens for your hives, or do not manage varroa at all and breed from any hives that do survive
- Drone trapping-place frames sized for drone brood in the hive and remove them before the capped drones emerge. Freeze the frames and repeat. The idea is to remove a percentage of mites with the drone brood and interrupt the mite population growth curve throughout the summer. Don’t do this if you can’t be 100% sure you can remove the drone frame before they emerge! If they emerge you have turned your mite trap into a mite bomb that will quickly overwhelm your hive.
- Powdered sugar treatments-sprinkle a cup of powdered sugar throughout your hive once a week for 4 weeks. By coating the bees with sugar, you encourage them to groom each other and they remove mites in the process. This doesn’t effect mites in the capped brood, so it has to be repeated as more mites and bees emerge.
- Screened bottom board-the idea is that mites fall off the bees and down through the screened bottom board and can’t get back onto another bee. Minimally effective at best.
- Brood break-splitting a hive and letting it requeen itself can set back the mite population enough that they can’t catch up and overtake the bees before winter sets in.
- Apiguard-a product made from thymol essential oils, may reduce queen laying and cause bees to beard outside the hive, treat twice at two week intervals, not for use during honey production
- Apilife Var-thymol, eucalyptol, menthol, and camphor oils, treat 2-3 times for a week to 10 days each, not for use during honey production, need to wait a month after treatment before adding honey supers since the oils can taint the taste of the honey
- MAQS-mite away quick strips. Strips impregnated with formic acid, which is a natural product. Formic acid is naturally present in honey and MAQS strips can be used with honey supers on. It kills mites in capped brood, but only works at temperatures from 50-92 degrees F. There are reports of queen loss and damaged brood, usually when MAQS is used at the higher end of its effective temperature range.
- Oxalic Acid-natural acid used in vaporization or dribbled onto bees. The dribble method can cause bee damage and should only be done once a year. Neither dribbling OA or vaporizing it in the hive is able to kill mites in capped brood. The dribble method is used once a year during a broodless period, generally midwinter. The hive can be vaporized once a week for 3 weeks at any time of the year.
- Hop Guard II-natural product derived from hops. It is safe to use with honey supers on, but is not legal in all states and works best when there is little to no brood present.
- Apivar (amitraz)-synthetic pesticide, added to the hive in a slow release strip that stays in the brood area for up to 2 months. The strips must be removed at least 2 weeks before honey supers are added and it leaves a residue behind on the wax and honey. Mites can become resistant.
- Apistan (fluvalinate)-synthetic pesticide, can harm queens and drone reproductive health, has a long half-life, leaves behind a residue in wax, cannot be used during honey production, mites can become resistant
- Checkmite (coumaphos)-synthetic pesticide, should not be used in colonies rearing queens, is not legal in all states, also leaves behind a reside and mites can become resistant, do not use with honey supers on.
What may happen to your hive if you don’t manage mites? You may see signs of PMS, or parasitic mite syndrome. When a hive has a higher level of mite infestation than they can handle, they start showing signs of PMS. In the adult bee population you may notice high mite numbers in your mite samplings, a dwindling of the adult bee population, crawling bees in the area in front of the hive, bees with abnormal wings, and repeated queen supersedures. The brood may be spotty and begin to show signs of diseases like foulbrood, chalkbrood, or sacbrood. Examination of the empty comb may show white granules, which are mite droppings. Eventually the adult population dwindles to an unsustainable level and the colony dies.
Varroa management is the most important issue beekeepers are currently facing. There is no way to not deal with mites. Even if you choose to completely ignore your mite levels and do nothing to help the bees cope, you are inadvertently choosing to select for survival genetics and should be prepared to lose anywhere between 0 and 100% of your hives every year.
I’ll admit I have not been very good at sampling varroa in my hives. 2015 was the first year I checked for mites, and I used the sticky board method on one hive. I saw mites on the board and treated the entire yard, but never rechecked to make sure my treatment was effective. I do not use any synthetic chemical miticides in my beekeeping operation, preferring to stick with naturally derived treatments instead. I treated with MAQS in August and one round of oxalic acid vaporization (OAV) right after Christmas. I had 100% overwintering success and my hives came out booming this spring. From here forward I am going to monitor at least a percentage of my hives on a regular basis, both before and after treatments. When I choose which queens to breed from, I want to have a history of how well they tolerate varroa so I can gradually improve the natural resistance in my hives. Without accurate records I would just be guessing, and that’s not my style.
For a more in depth look at varroa, check out Randy Oliver’s site at www.scientificbeekeeping.com. He does a wonderful job with setting up experiments and reporting his results.