Use of oxalic acid
Oxalic acid is an active ingredient that can only kill Varroa mites that are outside the brood cells. Therefore, the anti-varroa treatments carried out with products containing oxalic acid as active ingredient must be applied in complete absence of capped brood.
The factors to be considered in case of oxalic acid treatments:
- Available registered veterinary medicinal products
- Devices for trickling (e.g. syringes)
- Devices for sublimation (sublimators)
- Personal Protective Equipment: gloves, white overalls, gas mask with filters for organic acids
- Devices for caging the queen
Oxalic acid treatment should be administered in brood absence to ensure an optimal treatment efficacy.
The complete absence of brood can be achieved under natural or artificial conditions.
The complete absence of brood can occur:
- in winter due to cold weather as well as in summer,
- as soon as a natural swarm is collected,
- by carrying out a total brood removal,
- after caging/confining the queen.
Oxalic acid treatment is authorised in organic beekeeping (please check out also the national regulations). It is important to rotate the active ingredients used for treating the bees to avoid the development of drug resistance (although no resistance to oxalic acid is currently known).
Oxalic acid treatment can be applied by trickling the drug in liquid form (sucrose or glycerol solution) or by sublimation using various types of commercially available sublimators. In all cases, the instructions on the drug package leaflets must be followed carefully and Personal Protective Equipment must be used.
Liquid solutions can be dispensed with a clean syringe, by trickling slowly onto the bees when most of the bees are in the nest (e.g. early morning or late evening) so that most of the bees get in contact with the medicine. If the drug is administered in winter, warming up the solution might be advantageous.
Albeit the sublimation method for the administration of oxalic acid drugs is a very common practice, it has several disadvantages:
- the need to wear appropriate PPE (e.g. full-face mask with organic acid and dust filter),
- the risk of inhaling oxalic acid crystals that persist inside the nest,
- the need to purchase the sublimator,
- the difficulty in dispensing the drug and ensuring the all the bees get in contact with the medicament.
In terms of advantages, the sublimation of oxalic acid guarantees reduced time for simultaneous administration and allows the operation to be carried out without the necessity of opening the hives.
The sublimation should be started from the top of the hive, as the vapour generated are heavier than the air and it spreads by gravity more evenly inside the hive (and tend to precipitate downwards). It may be useful to rotate the cover to administer the sublimation treatment from above, to create a sublimation chamber and to optimise the distribution of the product inside the hive. The sublimation should be carried out when most of the bees are present in the hive (early morning or late evening). Sublimation should not be carried out with too low temperature as the treatment would not be effective if bees are clustering.
Warnings: May depend on the regulations in force in the given country.
Please check out the B-THENET Platform for the Best Beekeeping Practices tailored to each country in the national language, co-developed with practicing beekeepers in the National B-THENET Centres of those countries (Austria, Belgium, Croatia, Denmark, Germany, Greece, Hungary, Italy, Poland, Slovakia, Slovenia, Spain, Sweden).
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