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.

Rusty
HoneyBeeSuite

Comments

Aram
Reply

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.

Emily
Reply

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 : GardenFork.TV
Reply

Do you have any suggestions for which brands of organic acid treatments to use? thanks, eric.

Rusty
Reply

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.

steve
Reply

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

Rusty
Reply

Steve,

I haven’t heard of it. Anyone else?

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