Vaporizing to kill Varroa Mites

By Steve Winchell

Testing:

You can be sure that you have mites in the late summer and fall. I do not bother to test to see if I have mites, I just treat with Oxalic Acid vapor and see how many mites I kill. If I see no dead mites three days after I treat (which never happens), I will wait three days and treat again to see if I kill any mites. Remember that at any time, 60 to 75% of the mites in a hive are under the capped brood cells, so testing or treating with Oxalic acid can, at most find 25 to 40% of the mites present in the hive, and testing with an alcohol wash kills about 300 bees.

Frequency:

In the February 2018 American Bee Journal article “The Varroa Problem: Part 15”, Randy Oliver mentions that “some experienced European beekeepers recommend repeating the vaporizations at shorter intervals - every 4 days - in order to prevent any mites from exiting and reentering the brood between treatments”. Randy tested his spreadsheet model and saw a rapid drop in the number of mites using treatments every 4 days, but he tested with only 4 treatments over 16 days, so by the end of the time period of his model - 28 days -  the mite count came back up without further treatments. Since then, we have found out that the oxalic acid is only effective for 72 hours in the hive, so you really need to treat every 3 days. As for the number of treatments, you need to continue treating every 3 days, if you can, until you see no more dead mites for two consecutive treatments. 

Timing:

I like to vaporize in the morning before the field bees leave the hive for the day, that way I get more phoretic mites and there will be no, or at least fewer, bees returning to the hive while you are working, but around sunset is also a good time to treat. But as the days get cooler in the fall, you need to pay attention to the temperatures. The bees will start to cluster at 50 degrees, and the bees with the most mites are the nurse bees that are in the center of the cluster. The bees cluster close enough to keep in the heat, but this will also keep out the oxalic acid vapors, so to be effective, you should treat when the temperature is above 50 degrees, therefore you may find that your only choice is in the middle of the day.

Supplies:

· Vaporizer

· Car Battery

· Oxalic acid (sold as wood bleach at lumber stores)

· Masking tape for upper entrances or other gaps

· Damp cloths to block the lower entrance

· Bottom board inserts if using screened bottoms

· Mask rated for organic acid vapors

· Latex gloves (I use 9 mil) to keep the oxalic acid off your fingers

I place a damp cloth across the bottom entrance of each hive, then I use Masking Tape to close up the upper entrances and finally I insert the wooden boards under the screened bottom

I set the battery close enough to reach several hives then attach the cables to the battery to allow the vaporizer to pre-heat. I also place a small amount of Oxalic Acid into the vaporizer – about half the size of a Pea. I stand back and watch to see which way the wind is blowing – you do not want to breathe any Oxalic Acid Vapor! (You should be wearing a mask.)

When the vaporizer is heated up to temperature and the test Oxalic Acid is gone I take a deep breath and hold it (again, a mask is safer), pull the damp cloth aside and place the vaporizer in the entrance of the hive, I put 1/4 tsp scoop of Oxalic Acid per hive body into the Vaporizer, slide the vaporizer into the hive and replace the damp cloth. Then I step back (up wind) and breathe. (Note that the Oxalic Acid will melt and begin to vaporize as soon as it is placed into the hot cup so you will need to be very careful, you may want to wear a mask rated for this type of organic acid!) After about two minutes, all of the Oxalic Acid will be vaporized and out of the cup.

Take another deep breath and hold it. You can now pull aside the damp cloth and remove the vaporizer – be sure that it is empty before you remove it. I usually tap it on the side of the hive stand to knock off any ash, dead (cooked) bees or spilled Oxalic Acid before I go to the next hive. Note the time, you will want to leave each hive sealed up at least 10 minutes after you remove the vaporizer.

Repeat steps 3 and 4 keeping the vaporizer hot makes the process go fairly fast.

Depending on how many hives you have it may be time to go back to the first hive to un-seal it. Again, you will want to wait at least 10 minutes after you have removed the vaporizer before you un-seal the hive I spend this time putting the vaporizer and battery into my cart. I then start by removing the masking tape since there are always guard bees waiting at the upper entrances and if some field bees are out they will be gathered at these upper entrances waiting to get back in. Next I remove the damp cloth from the bottom entrance and finally I remove the board from under the screened bottom. I use the damp cloth to wipe any spilled Oxalic Acid and dead mites from the previous treatment from the board. I replace the board and leave it in for three days (until the next treatment) so that I can see how many mites I have killed. I repeat treating every three days until I see no dead mites after two consecutive treatments.