An Improved, But Not Yet Perfect, Varroa Mite Washer
I keep looking for a quick, easy, and accurate way to monitor mite infestation rates. I’ve happily used the mite shaker bottle for some years, but it has its shortcomings. I’d like to ask my readers to help me improve the design.
As I detailed in the July issue, the shaker bottle gives only about 87% recovery of mites. The vigorous shaking also tires my arm when I’m sampling from a number of hives. Since in some of the field trials that I run I need to repeatedly collect mite data for entire yards of bees, I decided to build a shaker table that could wash the mites from a dozen bee samples at a time.
In designing the table (by trial and error after error), in order to determine the best sort of container and agitation, I carefully studied the motion necessary to wash the mites from the bees (using small pieces of white paper mixed with the bees to track their movement). My first discovery was that vigorous shaking was entirely unnecessary! The problem with the shaker bottle is not that the mites don’t get dislodged—it is that they get caught up in the bees’ bodies above the screen as the alcohol drains down.
I found that mites immediately release their hold on the bees when they are immersed in alcohol, and can be dislodged by relatively gentle agitation. The trick is to make sure that all the bees get agitated, and that once a mite is shaken loose, that it can drop free of the bees into a reservoir below. This requires that the bees are constantly and loosely suspended in the alcohol, and that the fallen mites are not stirred back up into the bees again.
I found that the right circular motion in a tapered container kept all the bees suspended in motion above a screen, and that the alcohol reservoir below remained relatively calm. The second thing was how to recover the mites from the reservoir—when I tried a drain at the bottom, there was too much splashing of alcohol when I drained off the mites for counting. So I worked on a design with a nested filter that I could use to lift the bee sample free of the washed mites.
My “final” design is able to quickly obtain 100% percent recovery of the mites (confirmed by vigorously shaking and rewashing over 25,000 bees)! The design worked so well that I now use the new wash cups in the field. No more sore arms, and nearly 100% mite recovery in less than 30 seconds.
The wash cups are simple, cheap, and easy to build. Unfortunately, they are a bit too flimsy and heat-sensitive for rough and tumble field use (they can warp in direct sunlight on a hot day), but I have been unable to find better alternatives. So I decided to share what I’ve learned to date, and hope that someone more innovative than me can come up with a better design. Until then, the current design would be perfectly adequate for taking repeated samples so long as one handles the cups reasonably gently. So I sweet-talked my wife Stephanie into snapping some photos of me building and using the Improved Mite Wash Cup.
The mite washer uses two Solo (TP-16) 16-oz drink cups and one snap-on lid. You could probably scam a couple from a local restaurant, or order 50 online for about $10. Use a heated blade to cut off the lower portion of the cup at the existing indent.
Now take some bee package cage screen (which has a mesh size large enough for mites to pass through), and press it into a 70mm lid (regular Mason size), pushing it hard into the “corner.” Then cut off the excess around the rim of the lid.
Now flip the screen over and press the center down. Then use something with a point to lift it out.
Insert the screen into the bottom of the cup this way (cut edge down). Use a soldering gun and a strip of the cut-off portion of the cup to weld the screen to the cup in several places (this is the trickiest, but most crucial, step in the entire process). I have yet to find a glue (hot or cold) that holds well enough).
I found that the dimension across the top of the screen must be at least 2¾”– 2½” is too narrow (the bees won’t tumble properly). Also, the screen cannot project up on the inside of the cup too much, or again the bees don’t tumble. For this photo I flipped the screen upside down from the design that I’ve been using, in order to make it easier to weld. In my original design, the bottom of the screen was even with the cut edge of the cup, which lowers the screen slightly, and perhaps performs even better. Please experiment and let me know!
The screen cup now drops right into an unmodified cup. You can see the cutoff guide that I used near the bottom of the lower (uncut) cup.
In the apiary, pour some rubbing alcohol into the cup assembly. Ultimately, you will need at least ½” of alcohol above the bees. This cup works for a 1/2-cup (~300-bee) sample, but even better with a 1/3rd cup sample (about 200 bees). See http://scientificbeekeeping.com/sick-bees-part-11-mite-monitoring-methods/ for details on how to take a bee sample.
After you’ve dumped in the bee sample from a brood frame into the cup assembly, check to make sure that there is at least a half inch of free alcohol above the bees, snap on the lid, and then hold the cup loosely at arm’s length, with your arm hanging straight down. Swirl the cup in a small circular motion with a loose wrist. Watch the bees to make sure that you’ve got the motion right—that all the bees are tumbling.
The free alcohol above the bees, the tapered sides of the cup, and the friction of the screen at the bottom all seem to be necessary for a good tumbling action. The mites drop like rocks into the relatively still alcohol in the bee-free space below.
Swirl for 30 seconds (that’s exactly the amount of time that it takes to hum the “I wish I were an Oscar Mayer wiener” jingle twice through). I tested the recovery rate by washing 8 samples (averaging 30 mites each, counting the number of dropped mites every 5 seconds. I averaged 90% mite recovery in the first 10 seconds!
After swirling, simply lift out the screen cup containing the washed bees–the mites will all be in the cup below. It then takes about 15 seconds for all the mites to settle to the bottom (I prepare the next cup during this time). You don’t need to use this much alcohol for a 200-bee sample (which I’ve come to prefer for quick and dirty mite monitoring).
You can easily see the two mites from this sample. Since there were about 300 bees, divide by 3, indicating an infestation rate of less than 1% (one mite per hundred bees). For a 200-bee (1/3rd cup) sample, simply divide the number of mites by 2 to get your mite rate.
If you carry an extra outer cup and a teacup strainer, it’s quick and easy to filter and reuse the alcohol for the next wash.
I WANT TO HEAR FROM YOU
OK, it’s your turn! Please help me to figure out how to improve this design for a field-sturdy mite washer. I thought I had it with the clear acrylic Stir ‘n Sip cups that come with a plastic straw—but couldn’t make them work due to their narrowness. For now, I just carry a few of these cups in the truck. They make mite monitoring a breeze!
Update Dec 2013 I’ve now found similar clear cups made from polypropylene (e.g., Starbucks cold drinks). The recycling number on the bottom is “5.” These cups are stronger and much easier to heat weld with a soldering iron (and could be glued with MEK).