Fumigating with Acetic Acid to Decontaminate Brood Chambers

By Paul Kelly

The control measures for the honey bee gut parasite Nosema include:

  1. maintaining strong colonies with prolific queens
  2. ensuring that colonies have adequate stores of honey and pollen
  3. selecting apiary sites with good air drainage, wind protection and exposure to the sun
  4. feeding sugar syrup medicated with Fumigillin
  5. fumigating ‘deadout’ colonies with acetic acid before reusing them for making up new colonies

We have been fumigating our deadout colonies at The University of Guelph for over twenty years. It is a simple, inexpensive method of killing the Nosema spores in the honeybee feces that can be seen inside affected colonies. This method was developed by the British researcher L. Bailey and is described in a January 1957 American Bee Journal article. We have modified his methods somewhat.

Eighty percent, food grade, acetic acid is available from chemical supply companies. It is essentially a concentrated form of vinegar. Acetic acid is corrosive and needs to be handled with extreme care. Material safety data sheets should be provided when you purchase the acid. Read these thoroughly and follow all suggested safety precautions. Safety goggles, a respirator, rubber gloves and a rubber apron are required. Wash water should be readily available in case of contact with the acid.

Indoor Method

  • Heat an isolated and sealed room to between 25 and 30 degrees Celsius (77-86 F). This temperature should be maintained for the duration of the fumigation.
  • Stack brood chambers four high on a closed pallet. The bottom boards should be removed and burr comb should be scraped off the bottom and top of the frames to ensure that the boxes fit together tightly.
  • Place a glass pie plate or similar container on top of the frames in the top box.
  • Put an empty super on top of the brood chambers. Any holes in the boxes should be taped shut; minor cracks are not an issue.
  • Pour 500 ml. of 80% acetic acid in the container.
  • Cover the stack with a hive lid or inner cover.
  • Close the door and place warning signs in the appropriate locations to prevent accidental injury from exposure to the fumes or contact with the acid.
  • The acid will evaporate in approximately one week. Check after one week and leave for longer if necessary.
  • Air the equipment out for several days before using.

Outdoor Method

The same methods as above apply but stacks of brood chambers should be sealed as much as possible. Vapour barrier plastic, stretch wrap or tape can be used to seal the holes and cracks. Place the stacks in a location protected from the wind and with full exposure to the sun. This method will only work when outside temperatures are in the 20 to 30 degrees C range. Appropriate measures should be taken to prevent accidental exposure to the acid.

Fumigation with acetic acid is effective at killing Nosema spores but not American Foulbrood (AFB) spores.

Originally Published in the Ontario Bee Journal

Here is a source in Ontario for acetic acid: ANCHEM – Your Chemical Solutions