Varroa products fall into two groups, and the distinction shapes how a programme is built.

Organic acids

No established resistance has been reported; this makes them the solid leg of the programme.

• Formic acid: The only one that penetrates sealed brood, so it works even when brood is present. It is very sensitive to temperature: in heat it can harm the colony, in cold it is ineffective
• Oxalic acid: Reaches only mites on adults. Highly effective in a broodless period, weak when brood is present. Applied by dribbling or sublimation
• Lactic acid: Sprayed onto the bees. Suitable for small colonies and artificial swarms

Synthetic acaricides

Usually strips with long release. Effective and easy to apply.

Two significant drawbacks:

• Resistance develops. Reported worldwide in the amitraz and pyrethroid groups
• They can leave residues in wax. Fat-soluble substances accumulate and re-enter the cycle through foundation

Licensing

The product used must be licensed for bees in your country. A licensed product has a tested dose, known residue behaviour and a defined withdrawal period.

Preparing unlicensed mixtures means uncontrolled dosing, residue risk and accelerated resistance.

Rules of application

• No treatment while supers are on. Residues pass into the honey
• Observe the withdrawal period
• Follow the dose and duration on the label. Underdosing kills the susceptible mites and leaves the hardy ones; it accelerates resistance
• Do not leave strips beyond their period. A spent strip means a constant low dose
• Watch the temperature. Decisive with organic acids

Resistance management

• Rotate the active substance; the mode of action must change, not the brand
• Include organic acids in the programme
• Use non-chemical methods: brood interruption, drone brood removal
• Measure efficacy after every treatment

Safety

• Organic acids are corrosive; use gloves, goggles and a suitable mask
• Store products in their original packaging
• Record the product, date and dose; this is a legal requirement in many countries