parasites varroa mites

Of mites and men

Every year at about this time, new beekeepers overwhelm the social media with claims they can save the honey bee (and the world) with copious applications of powdered sugar. The onslaught is as predictable as the tide and just as insistent. I actually feel sorry for them. If they ever really studied the Varroa life cycle and how it complements the Apis life cycle, they would realize that powdered sugar is a great idea with very little promise as a long-term control.

So here, resurrected from an earlier post, is a quick rundown of the pros and cons in this contentious debate.

How it works

The theory behind powdered sugar dusting it that the bees will groom the sugar off themselves and the hapless mites will drop from the bees and fall through the screened bottom board and out of the hive. Mites on the ground soon become food for something else. Good riddance. Any inert powder applied to the bees will have a similar effect, but powdered sugar is a good choice because it is readily available, inexpensive, and harmless to the bees.

Most sources I consulted recommend one cup of powdered sugar per brood box. However, those who use bellows-type applicators use less. Those who use powdered sugar dropped through a food strainer use considerably more. As I said, the sugar is harmless to the bees, and even the small amount of corn starch found in commercial powdered sugar produces no ill effects.

Powdered sugar also has no harmful effect on mites. Some folks think the sugar makes it harder for the mites to hold onto the bee, others say it doesn’t affect the mite’s grip whatsoever. Most experts think it is simply the act of grooming that dislodges the mites: in an attempt to rid themselves of the sugar, they end up flicking away the mites. Consequently, most mite drop after a powdered sugar application occurs within the first few hours and decreases quickly after that.

What are the limitations?

Unfortunately, powdered sugar only affects phoretic mites. Phoretic mites are the ones riding around on the bodies of adult bees; they are the ones you can see. But by far the most mites, especially during spring and summer, are inside the cells of capped brood. These mites are protected by the comb and are unaffected by blizzards of powdered sugar.

That means that powdered sugar must be applied regularly to the hive in order to remove mites as they hatch along with brood. In his experiments, Randy Oliver found that the more treatments you applied, the more mites you “killed” (dropped out of the hive). Treatments every week killed more mites than treatments every two weeks, which killed more mites than treatments every month. Oliver found that the only treatment schedule that effectively suppressed mites over long periods was once per week.

But according to the University of Florida Institute of Food and Agricultural Sciences, when bee brood is present, a female mite may stay in the phoretic state from 4.5 to 11 days before she climbs back into a brood cell. That means that even with a once-per-week treatment schedule, many of the mites will evade the sugar dust completely.

Another factor is the method of application. Some experiments have shown the best coverage is achieved by removing every frame from the hive, treating both sides, and then replacing the frame. This is an egregious amount of work and a huge disruption of the colony, especially if done on a once-per-week schedule. Imagine the disruption to a triple deep hive if you were to tear down the colony once a week and dust both sides of each frame. In fact, except for hobbyists with just a few colonies, it would be virtually impossible.

Other experiments have shown that dusting the top bars only is fairly effective and more efficient, as long as at least some of the sugar immediately falls through to the bottom of the hive. But again, with multiple deeps, dusting the top bars only has very little effect on the lower boxes.

Another issue is humidity. Powdered sugar is amazingly hygroscopic, meaning it has an attraction for water. If you keep bees in a humid climate, or if your hives are full of moisture, the sugar will clump on the bees instead of dusting them, a situation that reduces the efficacy of the treatment. You end up with a hive full of bees and mites and clumps of wet sugar.

The good news

In spite of the negatives, sugar dusting has been found to significantly reduce adult mite populations at times when little brood is present. Colonies in a late summer nectar dearth or loosely clustered winter bees may be effectively treated with powdered sugar. Also packaged bees, swarms, and shook swarms—units without brood—may benefit from the treatment as well.

My own opinion is that powdered sugar dusting is effective only when little or no brood is present, and when it is used in combination with other Varroa management protocols such as drone trapping, queen sequestration, splitting, and the use of organic acids. Except under the most onerous treatment regimens that are highly disruptive to the colony, powdered sugar dusting by itself is insufficient for long-term mite management.



  • It might just be easier to take all the capped brood from one hive and give it to another. Then a week later donate the rest of the new capped brood to that hive. Now you have basically one hive that is full of mites and another that has donated all of it mites away in the capped brood.

    Limit the “mited” queen from laying until all brood hatches and then let her lay again. The mites will jump 3 or 4 at a time into these new larvae cells and basically commit suicide by killing the larvae. With that crazy workforce in the “mited” colony, it might actually even give you a bumper honey crop if done during the flow.

  • Great post Rusty. I went to a day of workshops on varroa run by our UK National Bee Unit Inspectors recently. They strongly emphasised that you cannot rely on sugar dusting alone to keep varroa levels down – if you do your colonies will die.

    • Eric,

      I have tried a number of different ones, but I have had best results with ApiLife Var. In fact, the years I used that particular product I was able to overwinter all hives successfully . . . other products, not so much.

      That said, I hate using the stuff. You have to remove honey supers and close up all vents and screens so the hive gets almost no airflow for three weeks. I don’t like the smell, the directions are confusing, and the bees tend to beard outside the hive because it gets hot in there with no airflow.

      However, it kills the mites, spares the bees, and is made from a naturally-occurring substance. Apiguard is a similar product but you have to make room for the gel container, something you don’t have to do with ApiLife Var. I had bad results from HopGuard and lost a lot of hives. I find formic acid (Mite-Away) a bit over the top. My bees reacted strongly to it so even though formic acid is naturally found in honey, I don’t like to use it.

      Generally, I use ApiLife Var one time (three weeks) in late summer and that’s it.

  • Was wondering, has anyone ever tried making their sugar water feeders with sulfur well water to help fight the mites?

  • Hi Rusty,

    Thanks for your blog. I’ve been reading it the last few years. A real wealth of useful information! I put in a sticky board to get a sense of the mites in my hive. Shockingly, after 24 hours I counted almost 400 mites. That being said, this hive has a lot of bees in it. I got the nuc in May and its got a deep with 3 medium supers packed full of bees.

    I’ve seen no big die offs or large numbers of larvae being pulled out..and while they guard the hive vigilantly on the porch, they’re docile when I go in the hive. (Typically, my hive’s demeanor has let me know if something going on in the hive needed attention.) I had decided since this is their first year to leave them the honey and thought I would harvest in the spring to be certain they have enough for the winter. But now I feel I should treat them…I don’t use chemicals in my garden or with my bees.

    I’m curious what your thoughts are on treating with essential oils? I have read that if you are going to use essential oils, you should take honey before…which then makes me wonder what are the oils doing to their honey you leave in the hive? As well as how do you determine how much honey you can take from a newly established hive…? My unfortunate experiences so far is I’ve left it all for the spring and none of my hives have made it through the winter in the past 3 years for various I just have extracted the honey then and gotten new hives. I LOVE having bees I have learned so much from them and find them endlessly fascinating…but this is becoming a depressing and expensive cycle of loss. Any thoughts or insights would be most appreciated.


    • Wendy,

      These are hard questions to answer. To begin, though, if you are going to harvest honey, you don’t want to expose it to essential oils because it will end up smelling and tasting like whichever oil you used. Use spearmint, for example, and it will taste like spearmint instead of like honey.

      If you got 400 mites in 24 hours you will lose this colony unless you treat, and I don’t think any essential oil will do it for you. Sometimes the essential oils can help keep the mite count down if it is low to start with, but you’ve got crazy many mites. And remember, it isn’t the mites that do in the colony but the viruses they carry that is the problem.

      If you decide to treat I recommend one of the preparations approved for organically grown honey, such as those containing thymol or formic acid. Even though we would all like to keep bees naturally, I’m not for letting them die every year. I think we have an obligation to either work toward breeding resistant bees (something you can’t really do with one hive) or treat in a way that suits your personal philosophy. But letting them die every year doesn’t benefit either us or them.

      • Thanks. I’m certainly not for “just letting them die” every year either, which is why I’m trying to determine what the best thing is to do. The number of mites with previous hives have been less than 50.

        • Wendy,

          Sorry if that sounded critical; it wasn’t meant to be. I thought you meant you lost all your bees during each of the past three winters. Anyway, the trouble with sticky boards is that the numbers mean different things depending on when you did the count. If you have lots of brood in the hive and a 24-hour mite count of 20 or 30, that is huge. If you have only a little brood, 20 or 30 isn’t quite as bad. I know people who treat at two or three mites. Another variable is the size of the colony, of course. More bees can support more mites. You may consider doing a sugar roll test, as this gives you a better (although still not perfect) idea of the actual number of mites. An alcohol wash will be even more accurate, but it kills the bees in your sample.

          As for how much honey to leave in the hive, 80-90 pounds is a good number, less if you live in the southern states.

    • Alex,

      You have to read the temperature parameters on the package and then compare them to what you have. I think you can find the information online so you will know before you buy it.

  • Hi Rusty! Thank you for the overwhelming amount of information on your site. I’m a new beekeeper, having gotten my first two hives last year. I was at a beekeeping meeting a couple weeks ago that talked about swarming and the benefits of catching a swarm. They were saying that swarms were superior genetic stock as they were strong enough to swarm but from reading your articles it seems like swarms could also have mites. Would this method of using powdered sugar be a good treatment to do when getting a swarm? And do you usually check swarms right away for mites?

    • Or maybe not a super generic stock, but just that they are stronger than getting packaged bees. Do you find this to be true or can spring swarms be laced with mites and disease?

      • Amy,

        I have no reason to believe swarms are stronger than packaged bees. Probably some are and some aren’t. A swarm may even arise from a fairly new packaged bee colony, sometimes only a couple of months old. Spring swarms will almost always have mites, and if they have mites, they probably have viral diseases, too.

    • Amy,

      If you live in the US, essentially all honey bees will have varroa mites. There is no harm in doing a powdered sugar treatment, although there is probably very little benefit unless you do it constantly, about twice a week. Do I check swarms right away? Not usually. I assume they have mites, however.

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