Summer Treatment for Varroasis Widely Used in Europe

This method has already been demonstrated on a video produced by Bayer, the manufacturer of Bayvarol.

Formic Acid Treatment is the only treatment to date (apart from heat treatment) which kills the Varroa mite in the Brood cells.

Heavy infestations on Varroasis found in German colonies during the summer are treated by a procedure which gives the beekeeper the opportunity to treat his/her bees immediately without contamination of honey harvest and hopefully save the bees by timely intervention. Using formic acid the treatment procedure is extremely simple but requires to be carried out methodically.

Equipment required

  • A measure of 60% concentrated Formic acid (1 Litre)
  • Acid proof gloves.
  • Safety spectacles or goggles.
  • Suitable particle filter face mask.
  • Suitable piece of absorbent material (a square kitchen sponge will suffice)
  • Large bucket (2 gallon size) full of fresh water.
  • Brood box with floorboard sealed (foam rubber strip will suffice) and a
  • Crownboard.
  • Spare brood box and a full complement of drawn brood combs.
  • Coloured drawing pins.


  • When Varroasis has been diagnosed in a colony nothing is done until early evening at which time the bees are subdued.
  • if the colony is not strong: Supers are removed and the bees are shaken from the frames in these supers in front of the hive. The bees will return to the brood box.
  • If the colony is very strong: All of the supers are removed and the bees shaken from the supers in front of the hive as in para 13. Another brood box filled out with drawn deep frames is placed on top of the original brood box with a queen excluder between the two brood chambers.
  • The honey supers are removed to a bee proof location.
  • The following day or as soon as possible after the above operations have been carried out a spare empty brood box is prepared by placing it on a floorboard with the entrance sealed and air tight (a strip of foam rubber or even a strip of rag will suffice!).
  •  A crownboard is prepared such that it can be placed on top of this spare brood box to form a closed lid. This lid is sealed later using masking tape or some other similar adhesive strip.
  • The infected colony is subdued.
  • All of the brood combs in the brood nests are examined.
  • All combs in which most or all of the brood is sealed are identified. Coloured drawing pins are used to mark these combs.
  •  All combs which contain mostly unsealed brood are also identified.
  •  A suitable absorbent material is placed on the floorboard of the previously prepared empty spare brood box.
  •  a square domestic kitchen sponge is suitable.

The following necessary precautions are taken

suitable mask, acid proof gloves and safety glasses are worn, and a bucket with fresh water is provided. (If at any time formic acid comes in contact with skin, wash copiously and immediately with fresh water.)

When removing gloves after procedures involving formic acid, wash gloved hands completely in fresh water to remove all traces of formic acid from gloves before attempting to remove them.)

  • The absorbent material is soaked with 40ml of 60% (percent) formic acid, using a veterinarians syringe.
  • The crownboard is placed on spare brood box temporarily.
  • All the bees are shaken from the previously identified frames containing primarily sealed brood back into the parent hive.
  • Each frame of sealed brood without bees is placed into the spare brood box containing the formic acid pad.
  • When the brood box is full or all of the selected sealed brood frames are inserted, the crownboard is put in place and taped closed. Making the box airtight.
  • The box is left sitting in sunlight for 90 minutes, the ambient temperature being at least 15c on the day selected for the above procedures.

The weather forecast is checked prior to the fumigation being done, forward planning makes it more possible to achieve the desired conditions.

  • After the fumigation exercise is completed the brood combs are replaced in any colony if more than one colony was treated. Gloves and other protection are still worn during this operation. Never be tempted to work with formic acid without suitable protection.
  • The procedure is repeated the following week, fumigating the combs in the infested hives which were identified as having primarily open brood at the previous inspection.

The residual formic acid on the returned combs is said to be lethal to the adult mites in the infested colony and appears to go a long way to reducing the adult mite population sufficiently to give the colony the chance to prosper.

The adult mite fall in the colonies is checked either weekly or daily as a matter of routine from then on, to plot the progress of any residual infestation. If after around 14 days from the final fumigation the mite fall is more than 5 mites per day the above described procedures are repeated.

The supers are returned to the hives around two days after the fumigation is done in each case. Formic acid exists in honey naturally and is no longer viewed as a contaminant by the veterinary authorities in Europe.

The dosage of formic acid has to be varied depending on ambient conditions and beekeeper experience.

Read all you can about the mite and get to know it well. Only in this way will you be able to keep on top of the infestations which will be a continuous presence in your colonies from the initial find.