The treatment that we use and recommend is actually a combination of two organic treatments that we have found to be highly effective for killing and/or removing varroa mites. First, we use powdered sugar dusting to rapidly dislodge large numbers of phoretic mites from the bees and remove them from the hive via the screened floor. Powdered sugar works by two means, the first being that it works like ball bearings under the feet of the mites and prevents them from maintaining a good grip on their host. The second thing that happens when powdered sugar is applied, is that the bees immediately start grooming themselves and each other in an effort to remove the sugar from their bodies, thus knocking off mites at the same time. Regardless of exactly why, minutes after the treatment is applied powdered sugar and mites will rain from the bottom of the hive and onto the ground below. Speaking of that, if you have a problem with particularly aggressive ants, you might want to leave your sticky board in place during and for a short while after this procedure to catch the sugar, so as not to attract them.
Note: It is highly recommended that you make your own powdered sugar for this purpose. Nearly all store-bought powdered sugars contain corn starch, which is used as an anti-caking agent. Bees cannot digest corn starch and since it's inevitable that they will eat some of the powdered sugar, it's best to make your own.
In combination with powdered sugar dusting, we follow up with the application of a thyme oil/mineral oil mixture that quickly kills large numbers of mites. The thyme oil vapors will remain in the hive for several days before they completely evaporate, which means that even mites that were in capped cells at the time of application may be killed when they emerge days later.
In order to get started, you'll first need to make some powdered sugar. This is easily done by pulverizing regular, white, granulated cane sugar in a blender set on low. You'll need 1/2 cup of powdered sugar per hive body, but don't try to process more than 1/2 cup at a time in your blender or you are likely to burn it up. It only takes about 30 seconds to pulverize each 1/2 cup of sugar. Take a good look at it each time you make a 1/2 cup, to make sure that it looks as powdered sugar should and, if necessary, shake it up and blend it a bit longer until the desired result is achieved.
Besides the powdered sugar, you'll need a varroa treatment screen. This is simply a piece of 8-mesh hardware cloth pulled tight and stapled to a wooden frame that fits over the top box of the hive. Its purpose is to keep bees from pouring out of the top of the hive while you are treating.
Lastly, you'll need a small drip-bottle of thyme oil, a 32-ounce bottle of food-grade mineral oil, and a small squirt bottle. Open the bottle of mineral oil and add 18-20 drops of thyme oil to it. Close the bottle back up and shake it vigorously to mix the oils together. Pour a small amount of the mixture into the squirt bottle and then store the rest away for future use.
Now that you have the essentials, put your tool box together before heading out to the hives. Add to the items listed above, a well lit smoker, a roll of paper towels, a hive tool, a bee brush and a brand-new, small (2 inch), inexpensive bristle or foam paint brush.
Once you've got everything you need, get suited up and head on out to the first hive you'll be treating. As always, smoke the bees lightly through the entrance and/or the screened floor before opening the hive. After a moment, remove the roof, the quilt and the window screening. Use your smoker to convince the bees that are starting to pour out of the top to go back down into the hive. Use your bee brush to move any stubborn bees out of the way before placing your varroa treatment screen onto the top of the hive, as is shown below.
Most of the time your hive will consist of only two hive bodies when you are doing varroa treatments. Occasionally, you may have three for whatever reason, but you should never have more than that if you are managing your hives properly. Remember that you need 1/2 cup of sugar per hive body.
Once your varroa treatment screen is in place, pour, as evenly as possible, the first 1/2 cup of sugar onto the screen.
Next, use the paintbrush to work the sugar through the screen, between the top bars and down into the hive. Again, try to get the sugar as evenly distributed as possible.
Once you've worked in the first 1/2 cup of sugar, do the same for the next, and then the third if you're using three.
By now, your bees are working so hard to get all of this sugar off of their bodies, that it is highly unlikely they will any longer have interest in what you're doing. You should be able to remove the varroa treatment screen without being bothered by them, but before you do, prepare for the next step.
Tear off two sheets of paper towel and fold them at the perforation so that they are doubled up. Set the double paper towel on the varroa treatment screen and use your squirt bottle with the thyme oil mixture to make a # type pattern on the towel.
After you've applied the oil mixture to the paper towel, remove the varroa treatment screen, with the towel still on it, and set it aside somewhere. There will still be some powdered sugar on the top bars that you were not able to brush off through the screen. Since the bees are now quite occupied, you should easily be able to use the paint brush to clean off the top bars and brush the remainder of the sugar down into the hive. Once you've done that, place the paper towel, with the oiled side down, on the top bars. This paper towel can remain on the hive indefinitely, but if you do subsequent powdered sugar treatments, you should replace it with a fresh one. You are now ready to reinstall the window screening, the quilt and the roof and move on to the next hive to be treated.
Within minutes after closing up the treated hive, powdered sugar, hive trash and mites will start to build up on the ground below. Again, if you have significant trouble with ants, leave a (dry) sticky board under the hive for an hour or so to catch the mites and powdered sugar, rather than letting it all land on the ground, and slide the sticky board out and empty it into a small trash bin every 15 minutes or so during that time. Looking closely at the photo below, you can see at least a dozen mites that have been removed from the hive. This photo was taken just minutes after performing the treatment.