Formic Acid Therapy in the Fight Against Varroa destructor

Formic acid is one of the most effective tools in the modern beekeeper’s arsenal, valued especially for its unique ability to penetrate through the cappings of brood cells, which allows the elimination of mites feeding directly on the brood. As a saturated organic acid it occurs naturally in floral honeys and is considered safe for the quality of bee products, provided that the appropriate technological protocols are observed.

1. Technical parameters and environmental conditions

The success of the treatment depends on precisely matching the acid concentration and evaporation rate to the external conditions.

• Concentrations: Technical formic acid at concentrations of 86% to 99% is used for therapeutic purposes. The 60% concentration is also frequently encountered, recommended for top-dosing methods.
• Temperature: The optimal range of external temperatures is 14–25 °C. Permissible lower threshold: 10–12 °C. At temperatures above 25 °C evaporation becomes too rapid, posing the risk of losing the queen or killing the brood. Below 8 °C the acid crystallises and loses its effectiveness.
• Density: Concentrated formic acid has a density of approx. 1.2126 g/cm³.
• Evaporation rate: The safe standard is evaporation of approx. 10 ml of acid per day.

2. Application methods

Formic acid can be administered by various methods, each of which requires strict safety precautions (use of gloves, protective goggles and a respirator).

Polyethylene bag method (Most popular)

1. Preparation of the insert: Place three sheets of cardboard 3 mm thick and 15x25 cm in size into a polyethylene bag measuring 20x30 cm.
2. Dosing: Pour 30–50 ml of concentrated acid (86–99%) into the bag and seal the upper edge tightly.
3. Activation: Once the acid has been fully absorbed by the cardboard, make two holes with a diameter of 1.5–2 cm on one side of the bag.
4. Application: Place the bag holes-down on the frames above the centre of the brood nest, using spacer strips 1–1.3 cm high.

Bottle with wick method

1. Pour 30–50 ml of acid into a 100 ml bottle.
2. Insert a cotton wick, leaving 2–3 cm protruding outside.
3. Hang the bottle on an empty frame placed between the outermost combs of the brood nest.

Specialised evaporator method

1. Fill the evaporator body with hygroscopic material (cotton wool, gauze) and pour in up to 50 ml of acid.
2. Unscrew the cap by 1–2 turns to create an evaporation gap of approx. 1.5 mm width.
3. Place the device on the frames under the crown board, close to the back wall of the hive.

3. Treatment schedule and prevention

• Timing: Treatments are carried out twice: in spring (May, after the cleansing flight) and in late summer/autumn (September, after the honey harvest).
• Frequency: Two series of treatments are carried out as standard, 12 days apart. The exposure time of the acid in the hive should be 3–5 days. In the case of long-acting evaporators, the treatment may last 8–14 days.
• Ventilation: During treatment, closing the entrances is not permitted; they should be fully open.

4. Overview of additional applications

Formic acid at lower concentrations finds use in the disinfection and prevention of other diseases:

• Disinfection of combs and hives: A mixture of 10% hydrogen peroxide and 3% formic acid is used (or 0.5% acid in cases of septicaemia).
• Addition to syrup: For health purposes, a 10% solution of the acid is administered at a dose of 2 tablespoons per 3 bottles of syrup.

A correctly carried out formic acid treatment achieves an effectiveness of 75–97.7%. The key to success is avoiding hot weather, ensuring free ventilation and rotating preparations every 3–4 years to prevent the development of resistance in the parasite population.