Oxalic Acid
Oxalic acid is a cheap, easy, non-contaminating and effective mite treatment.
Methods
Oxalic acid is distributed in a beehive by two methods. One method involves spraying or dribbling an oxalic solution. It has the same drawbacks as using powdered sugar. A second method involves sublimating oxalic acid by heating it to about 300 degrees F. There are very few drawbacks to using oxalic vapors.
Building an oxalic evaporator is simple. It can be built in less than five minutes and will cost less than $10. Ace Hardware Stores carry all the parts. My evaporators consist of two parts, a magazine and a distributor. The magazine is filled with oxalic and is screwed onto the distributor. The device is inserted into the hive. Then it's heated with a propane torch.
The distributor is the part of the evaporator that distributes the oxalic vapor from the magazine into the hive interior. Different kinds of distributors can be built to accommodate different hive configurations. It's actually harder to describe an evaporator than it is to build and use one.
I have built two different kinds of evaporators. My vent evaporator fits into a 3/4 inch hole drilled into a super. My entrance evaporator is inserted into the hive entrance.
Vent Evaporator
The distributor, shown on my finger tips, consists of a brass 3/4" adapter with the threads ground down on a taper to fit in a 3/4" hole, a long 2" nipple, and an L.
Tightly assemble these parts together using Teflon tape and a pipe wrench. Grind the threads on the 3/4" adapter down on a taper. Leave enough of the threads so that they will securely bite into the wooden edge of the hole in the super.
- The magazine, shown on my palm, consists of a long 2" nipple, and a cap. Tightly assemble these parts using Teflon tape.
- When the magazine is hand tightened onto the distributor, it looks like this. And it is attached to hive as shown.
- Make sure the threads are seated in the wood which will hold the adapter securely in place. If the threads are just seated in propolis or wax, the adapter will fall out when it's heated.
New Prototype Vent Evaporator
I have been experimenting with a different vent evaporator. This evaporator is made out of ½" copper pipe, a 45 degree elbow, two caps and five small screws. It is assembled with Teflon tape and held together with the screws. Brazing could be used to replace the screws. Don't solder it together.
The small piece in my palm is a measuring cup. It is not heated like the magazine. It can be cut off at the proper length for the right dosage. After filling it with oxalic, it is inserted into the evaporator. The evaporator is rotated into an upright position and rapped a few times until the oxalic falls out of the measuring cup and into the evaporator. The measuring cup is removed and the evaporator inserted into a 3/4" hole drilled into the hive body. It is heated at very low heat for 3 to 4 minutes.
The thinner metal heats and cools faster. I don't use water to cool it. There is less condensation in the evaporator with the 45 degree elbow. And the measuring cup is easy and cleanly filled.
I wondered about the longevity of the Teflon tape and the screws. So far, no problem. This evaporator can be built for less than $3.
Entrance Evaporator
The entrance evaporator is inserted into the hive entrance. The distributor consists of a length of 3/8" OD copper tubing, a compression fitting, and an L fitting. These are tightly assembled using Teflon tape and a pipe wrench.
The magazine consists of a nipple, and a cap. Tightly assemble these using little Teflon tape.
When the magazine is hand tightened onto the distributor is looks like this.
New Prototype Entrance Evaporator
I have been experimenting with a new entrance evaporator. It's constructed like the copper prototype vent evaporator with an additional piece of copper pipe. This pipe is flattened on one end. It is inserted into the elbow after the evaporator has been charged with oxalic.
I expect the Teflon on the inserted pipe will need to be replaced more often, but it should work for beekeepers who prefer to treat from the bottom. This evaporator has all the advantages of the thin metal and 45 degree elbow. This model resists the plugging that sometimes occurs on the brass model.
Evaporator Operation
The basic operation is the same for all evaporators.
Read and understand the information in an oxalic acid MSDS. They are available on the internet. Basically, don't get it in your eyes, breath the vapor or dust, eat it, or leave on your skin. Don't underestimate the vapor's effects. It is composed of steam, formic and oxalic acid. If you have handled caustics, it won't surprise you. But if you haven't, take every precaution.Use the appropriate safety gear. This is a no-brainer. How many dead mites would you trade for your kidneys and lungs?
- Remove the magazine from the vaporizer.
- If using the entrance evaporator, make sure the tubing isn't plugged. I've plugged up mine by spearing a propolis lump on the bottom board. If the tube is plugged, oxalic vapor will vent around the magazine threads. But most of it will condense next to the plug in the tubing creating a super plug. The tubing can be heated to remove plugs. When in doubt, run a little water through the tubing to check the flow rate.
- Fill the magazine with the proper amount of oxalic acid. Research indicates that 1.5 to 2 grams per super is sufficient. By coincidence, my magazine, when filled to capacity, held just the right amount for my hives. This allows me to fill the magazine without using any measuring devices. The open end of the magazine is inserted into a small plastic bag containing oxalic acid powder. The powder is manipulated through the plastic into the magazine. There's very little exposure.
- Attach the magazine to the vaporizer. Hand tighten it.
- Insert the vaporizer into the hive entrance or twist it into the vent hole if using the vent evaporator.
- some recommend sealing the hive up while treating. Paper towels can be used. They can be reused for other hives and then tossed. I have found little difference between sealed and unsealed hives. As my hives don't have any upper ventilation, I no longer seal up my hives.
- Heat the magazine until the oxalic acid is vaporized. I use a propane torch running on the lowest setting for 4 minutes. Vapors will be given off at about 1 1/2 minutes. At about 3 minutes, most of the oxalic will suddenly vaporize. Start heating the flat face of the L and gradually shift the heat downward toward the magazine. Oxalic sublimates at about 150 degrees C. It decomposes at about 180 degrees C. Remember you are sublimating oxalic not smelting copper or brass:>)
- Cool and remove the vaporizer. The vaporizer can be cooled by pouring water over the brass.
- When it's cool enough to handle, remove the vaporizer from the hive and recharge it. Be sure the magazine threads are dry before filling or the powder may stick to the magazines threads.
- Ten to fifteen minutes after treating the hive, remove all the stuffing and let the bees out, if you have sealed up the hive.
- Cleanup. Clean the vaporizer with hot water. Then wash hands, etc.
- Store the vaporizer and the oxalic acid powder in a very safe place away from children and pets.
Vent or Entrance Evaporator?
I've tested both types of evaporators and found little difference in their effectiveness. But I like the vent evaporator much better when the bees are flying.
- Hive activity is not disrupted by its use.
- The beekeeper can stand and effectively treat from any position.
- The flame and heat are away from the beekeeper, flying bees and ground vegetation.
- The distributor is maintenance free.
The entrance evaporator will work with hives lacking the vent holes. In theory, it should distribute the oxalic fumes more effectively than the vent evaporator. But I haven't noticed any difference in practice. It should be more effective when the bees are clustered. If I were treating when the bees aren't flying, it would be my choice.
12 Volt Electric Evaporators
An electric evaporator has some advantages over one heated by a torch. They are faster, as no cooling time is required between hives. And all the heat/vaporization occurs inside the hive and away from the beekeeper. And there are no matches or open flames, an important factor when the fire danger is high. The only disadvantage I've found is that they can't be used in a hive with a migratory bottom. They are just too fat.
Heilyser, a Canadian company, offers several different models. If I had lots of hives to treat, I would strongly recommend using their electric model. These folks make a great product and provide great service/support. I originally bought an evaporator from them. It was a fine piece of machine work, but wouldn't fit in my hive entrance, as I use migratory bottoms that create a 3/8" entrance.
Some beekeepers have built electric evaporators using diesel engine glow plugs/igniters. See: dalcolapiaries or drobbins
Commercial Equipment
Several types of oxalic acid vaporizers are on the market. The European version is basically a 12 volt, electrically heated pan. Eastern European models are very elaborate with pumps, heaters, etc.
Cowan has a commercial prototype in the works.
