IPM 5.5 Fighting Varroa 5.5: Biotechnical Tactics II
The Oliver 15-second sugar dust method
Before I even considered advocating sugar dusting, I knew that no one with more than a hive or two would be out there using the suggested application methods of flour sifters or squeeze bottle puffing. It was far too time consuming! So I bought 50 lbs of powdered sugar from my local baker (it’s cheaper that way) and set out to see if I could come up with an easier, quicker method. I did.
1. A 5 gal bucket with a screw top lid to hold the fine confectioner’s sugar. Hobbyists can use any airtight kitchen container. Large operators may wish to use a rectangular plastic waste basket on a caddy that also holds the screen.
2. A bee brush with a 1-cup measuring cup taped to the handle (large operators will need a cup with a strong handle). Fluffing the sugar once by tipping the bucket will make it much easier to scoop.
3. A wood-rimmed moving screen of (strong) steel window screen. The rim should be ¾” on the top side (to contain the sugar), and at least 3/8” on the other (to space the screen above the top bars). I used 1/8” hardware cloth at first—it’s faster to sift, but doesn’t do as good a job at breaking up the lumps of sugar.
4. The colony should be on a screened bottom (I’m assuming this, but have not tested to see if it’s truly necessary).
1. Smoke the colony.
2. Remove the cover and smoke the bees down off the top bars.
3. Put the moving screen over the frames, and then use the cup to spread powdered sugar on the screen over the cluster area. Use 1 cup (approx. 100g) for 1-story colonies, or 2 cups for double deeps.
4. Flip the brush around, and use it to sift the sugar through the screen.
5. Lift the screen, and continue to use the brush crosswise across the top bars to sift the sugar into the beeways.
6. Replace the cover. We do this entire operation handily in less than 15 seconds!
7. Mites will begin to fall within seconds. If you’ve put a dry stickyboard under the screened floor, you can get a good indication of your mite level in an hour.
Tools for the Oliver 15-second sugar dust. Note the cup duct taped to the brush handle as a time-saving measure. Window screen in wooden frame.
Use one cup of sugar for singles, two cups for doubles.
Brush the sugar through the screen over the cluster of bees.
Lift the screen, and brush the sugar crossways across the frames so that it all falls on the bees. The whole process takes less than 15 seconds!
Kill two birds with one stone by combining dusting with other hive procedures. Feeding pollen supplement here.
This is a frame from the bottom brood chamber of a double, two minutes after dusting the top bars of the upper box with two cups of sugar. Note the sugar that has fallen through onto the top bars, and onto the bees and combs.
Close up of the bees from the frame in the previous photo. Note the sugar dust on their bodies, even though we dusted the box above.
1. In this case, more is better. Use enough sugar so that some falls through the screened floor.
2. Test your technique by pulling frames of bees from the bottom box in about two minutes. They should be obviously dusted white.
3. Keep yer powder dry! Damp powdered sugar clumps too much to dust the bees efficiently. Store it in a warm, dry place.
OK, sugar dusting has a proven track record, a mathematical explanation for its efficacy based upon mite population dynamics, and can be done quickly and cheaply (less than 25¢ to treat a 2-story colony). Why does it work, and will it harm my bees? Luckily, this question has largely been answered, both from practical experience, and scientific research. Sugar dust adheres to a mite’s ambulacra (foot pads) (Fakhimzadeh 2000), apparently causing the mite to lose its grip on the bee. Dusting may, in addition, stimulate bee grooming behavior (Macedo & Ellis 2002). It is a mechanical method of mite control, rather than chemical. It does not directly kill the mites—they fall out of the hive and can’t return. Fakhimzadeh (2001) found that direct heavy dusting resulted in greater mite drop than light blow dusting, and that no sugar particles were found in the bees’ trachea (breathing tubes). Heavy dusting may cause significant egg removal, and loss of a fraction of the older larvae (Aliano & Ellis 2005). This loss would be of little consequence, since a portion a day’s quota of eggs represents a relatively minor investment to the colony. Fakhimzadeh (2001) also found that dusting at frequent intervals did not appear to affect brood production, colony strength, queen survivorship, or honey production. Note that he dusted with less sugar 15g (about 1/8 cup per colony) than is currently recommended. His control of mite buildup was also less. I have not heard reports of problems due to dusting with 2 cups per colony.
There are drawbacks to sugar dusting. First, its application is dependent upon fair weather. It may also draw ants. Janet Brisson reported that sugar dusting during a nectar dearth may initiate robbing. I suggested that she try the old trick of removing all the hive covers in the apiary when you begin. That stopped the robbing problem. The question has arisen as to the best time of day to dust. I don’t know. Most mites hang out mostly on younger bees around the brood nest, so it may not be important to dust all the foragers. We still have lots to learn!
Some practitioners suggest banging the side of the hive after application to dislodge the sugar and stir up the bees. This makes sense. I’ve had an additional brainstorm: I’ve figured out how to effectively infuse powdered sugar with menthol, in the hope that it will agitate the mites, and cause more to drop. But first I need to test it to see if it kills brood. I’ll keep you posted on the results.
The beauty of sugar dusting is that you can do it as often as needed to control the mite. If your bees pick up extra mites from collapsing colonies, hit ‘em with sugar. Use the “Shoot first and ask questions later” method of dusting and taking a mite sample at the same time with a stickyboard (it doesn’t need to be sticky if you use enough sugar so that it falls on the board). If you see a lot of mites, dust weekly; if there are few mites, wait a month. When your colonies are broodless, a few sugar dustings would be expected to knock the snot out of the mite population, since they are all exposed to sugar at that time. I’ll try to get some numbers next winter.
I have been corresponding with the California Department of Pesticide Regulation. I explained how sugar dusting (and grease patties for tracheal mite control) were used, and asked them for an opinion as to whether they would be considered as pesticides, and therefore subject to regulation. Their response was:
“Randy, the two products of discussion are food products that are
normally consumed and have labels that do not make any pest control
claims. The way you are using them is to either create a barrier to the
mites or mask the smell of the bees so the mites won’t be attracted to
them. These actions are usually not thought to be methods of pest
control that need to be registered. These are like home-remedies. As
long as the food product labels do not make any pest control claims
like kills, controls, repels, etc. mites in bees, these are not
pesticide uses and do not have to be registered.”
Surprise—powdered sugar dusting really kills drops a significant proportion of the phoretic mites, and that exerts a strong effect on mite reproduction. It’s safe, doesn’t hurt the colony, can be used even when they’re storing honey, works any time of year that the bees are not in tight cluster, is cheap, and only takes 15 seconds! If you use an insert, it will even tell you how soon you should dust again.
The one-two punch—30 seconds to knock out varroa!
Drone brood trapping and sugar dusting—what a combination! The first punch gets mites in the brood; the second knocks them off the bees. Do them both at the same time every four weeks during spring, and sugar dusting alone at other times as needed. It’ll take you 30 seconds at colony, and cost you less than a quarter. Doesn’t get much better than that!
Either or both of these methods can be used during a honeyflow! I have not yet tried dusting down through the honey supers, but I imagine that the technique would be more effective if you lifted the supers and dusted the top of the brood chamber. Better yet, get the mite level down before supering, so you can wait until you pull the honey (but don’t wait too long).
Now let me be clear. I have limited experience with sugar dusting myself. I’ve dusted about 100 lbs of sugar so far, and have the technique down, but have not yet used it in my operation to any extent. We dusted 80 colonies in an almond orchard this spring, but there was not enough mite drop to make it worthwhile to dust the rest at that time. But I’ll sure be dusting later this season! I’ll let you know how it goes.
Update January 2015–we no longer use sugar dusting, as it simply takes too much time for the amount of benefit. Feedback from hundreds of small-scale beekeepers who have relied on sugar dusting alone has not been favorable. We have far greater success with thymol (Apiguard), formic acid, and oxalic acid (when colonies are broodless).
My new website
I’ve had requests from all over the world for reprints of my articles. I thought of combining them into a booklet, but realized that it would be out of date as soon as it was printed. So I decided to start a website for the express purpose of summarizing the state of knowledge on varroa management, general beekeeping, and California almond pollination, based upon practical application of scientific research, commercial experience, and tested methods from all countries. My goals are to keep it a concise source of information for the busy beekeeper, and to update it with feedback from readers, researchers, and field evaluation. It should be up by the time you read this! Log on to randyoliver.com.
I wish to thank Janet Brisson, Zion Guinn, Joe Carson, Jerry Hayes, Marion Ellis, and the students from Nevada County Science Center, who counted mites and bees. I especially appreciate the generous donation from the 2007 Honeybee, Beekeeping, and Environment Symposium sponsored by Summerfield Waldorf School and Beekind, Sebastopol, Calif. in support of my ongoing research.
Coming next month: Chemical weaponry—the IPM fallback position
Tips: Put a 3/4″ rim on both sides of the screen frame. By having more clearance above the top bars, dusting goes faster. Always check to make sure some excess sugar falls through the screened bottom–this tells you that you have used enough sugar. Avoid dusting on windy days!
Q: Can I use ordinary powdered sugar from the store, even though it contains starch?
A: I have not heard of any negative effects upon the bees due to the small amount of starch, even from beekeepers who have been dusting for years. This question has been debated ad nauseum on the Web. Starch naturally occurs in some pollens, and bees seem to be able to process it. You’re only talking about some 200 micrograms of starch per bee per dusting. I will be performing experiments on confined bees to see if the small amount of starch is a problem. As of this time, go ahead and use normal powdered sugar from the grocery. If you purchase it from a bakery in bulk, ask for the finest grind.
Q: How often should I trap and dust?
A: Start in spring as soon as the bees begin foraging. You want to minimize colony disruption. Every time you pull the drone trap frame, you stand a chance of injuring the queen. Try trapping and then dusting on the same visit every four weeks (28 days). Take a one-hour mite count (see below) to see if you can wait another month. I’m working on finding if a 10-minute mite count will work.
Q: What is the “threshold” number of mites after a dusting, that would indicate that dusting should be repeated in a week?
A: I do not have a number at this time, but will soon be running experiments to find out. Let’s do a little theoretical math: Let’s say that you don’t want the mite level to get above a 2% infestation. Therefore, you’d be concerned if the level approached 1%, since it could double in a month. Please refer to my Strategy article. You can accept a higher infestation late in the season than you would accept early. In spring, you might want to keep the level below 1/2%.
If a colony has a 1% infestation of the adult bees, and there are 30,000 bees (moderately strong), then there would be 300 phoretic mites. If dusting knocked off one third of those in the first hour, you would get a count of 100 mites. Therefore, until I get further data, I’d dust in two weeks if you got a 1-hour post-dusting mite drop of 100 mites from a moderately strong colony. Early in the season, try to keep the count below 50 mites dropping in the first hour.
Q: I am a new beekeeper this year so please keep this in mind. The question that I have is: what makes the bees decide to fill the bottom of your frame design with only drone comb rather than establishing worker comb? I love the simplicity of your design and plan to incorporate it into my hives.
A: This is normal bee behavior during a spring nectar flow for any space at the periphery of the broodnest. It is also normal to store honey at the top.
Q: Should I use the drone trap frame in a starting colony that is still in the first brood box?
A: Updated 7/25/07 Trap frames appear to work best in the upper brood chamber, generally position 3 or 4, in the springtime.
Q: Do I need to break down the brood chamber to dust?
A: Based upon the photos in the article, I’d guess no, but have not confirmed this experimentally.
Q: Can I dust with honey supers on?
A: The method does not contaminate your honey, so the answer is yes. However, the supers may need to be lifted, in order to effectively dust the top of the brood chamber. I’ve had some success in dusting 3-deep colonies by using 4 cups of sugar, but the bees in the bottom brood chamber do not get covered as evenly as when you dust a double deep with 2 cups.
Q: I was wondering if you have a plan for your drone trapping frame you would be willing to share.
A: Yes. Cut the ends off a grooved top bar. Saw a strip of plastic worker foundation to 2-1/2″, turn the top bar upside down between the end bars to pinch the foundation in place, and nail in place. The amount of exposed foundation should be 1-7/8″ or less (or some colonies will raise a line of worker brood at the bottom). Some plastic foundations have raised cells, and the cut edge won’t fit into the existing frame grooves (Permadent works well). If necessary, you may have to use a table saw to cut the grooves wider before you assemble the frames.
Q: What do you think of adding a drone frame 2 weeks apart, one in the top hive body and one in the bottom hive body? Would this set them too far back in worker brood or could it possibly maximize mite harvests? One frame in each box may also target mites in each box?…
A: I’d just do the top box with my design. Less colony disruption, With my frame design, bees would put worker brood in th top section of the frame if the frame were placed in lower box. It might expose more mites to the frame, but might not be worth it due to additional colony disruption, chance of killing queen, and time to split the boxes.
Q: I think 4 weeks is a little too long to keep drone brood in. I work in a 2 to 3 week rotation, but with the rain and traveling, it was almost 4 weeks before I was able to get into the hives and the drones had started to hatch out.
A: The ideal timing would be as soon as all the drone brood is capped. That could theoretically happen as early as day 13, if the bees built comb in two days, then the queen layed eggs in every cell in one day. However, that is unlikely to happen. Remember, each individual drone cell only traps mites on days 8 and 9—none before, none after. So removal at 2 weeks might render the mite trapping largely ineffective.
Giving an allowance of three days for the bees to build comb before the queen starts laying, the trap frame would begin trapping mites on day 11. Removing the comb at week 3 would allow 10 days of trapping, but you’d still have a safety margin of 6 days left before the first drones could emerge (and release mites) on day 27.
Waiting until day 28 (4 weeks) you might have a few drones hatching, but you would have far more mites still trapped in the frame. So my recommendation would be: if you have the time to check the frames at 3 weeks, and most of the drone brood is capped, replace it. This timing would give the greatest efficacy, but only if there is little open drone brood remaining on the comb. Otherwise, just wait for 4 weeks, for a no-brainer timing.
Even simpler–cut out drone brood any time after it’s capped, but not before. Be sure to cut it out before it emerges!
Q: Can I use an empty frame in the nest as a drone trap, or is having some comb overhead for honey important?
A: Sure, the only reason for split frame is to make it easier to save the bees’ honey while cutting out the drone comb.
Q: Or can an I use a frame with drone size wax foundation without the wires for each month’s treatment?
For some good graphs showing the importance of drone brood for varroa population growth, see http://www.csl.gov.uk/science/organ/environ/bee/diseases/varroa/varroamodel.cfm
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