Oxalic Acid by Vaporization (Sublimation)
Behandlungsmittel
In vaporization, crystalline oxalic acid dihydrate is heated in an electrically heated device until it sublimates.
In vaporization, crystalline oxalic acid dihydrate is heated in an electrically heated device until it sublimates. The resulting vapor spreads through the closed hive and settles as a fine crystalline film on bees and combs. The mites absorb the acid through contact. Unlike trickling or spraying, no liquid is introduced into the colony. Physically, the method is delicate: oxalic acid sublimates at about 157 °C but already decomposes from around 190 °C, partly into formic acid. The temperature control of the device therefore determines whether any active substance reaches the colony at all.
Vaporization, too, is a purely contact-based method and only reaches the mites sitting freely on the bees. Mites in the capped brood remain unaffected. Treatment is therefore tied to broodlessness and is used as a final mite treatment in late autumn or winter, at outdoor temperatures of about 2 to 10 °C and without flight activity. In the broodless colony, efficacy rates of around 95 percent are achieved, comparable to trickling and spraying.
The authorization status is decisive. For years, vaporization was not permitted in Germany because no veterinary medicinal product approved for it existed. Since September 2023, an approved powder for use in the hive has been available, which makes the method permissible. However, this authorization is not a general release of oxalic acid vaporization: only the approved product may be vaporized, at the approved dose of 2 grams per colony, and expressly only with the two vaporizer models for which efficacy and safety data are available. The Federal Office of Consumer Protection and Food Safety has made clear that no data exist even for other devices that appear structurally identical. Cold fogging of oxalic acid is not approved.
User protection is regularly underestimated with this method. Sublimation produces a fine oxalic acid dust in the air that strongly irritates the airways, eyes, and mucous membranes. Long-sleeved protective clothing, acid-resistant gloves, tightly fitting safety goggles, and an FFP3 respiratory mask or a suitable gas mask are required. Simple FFP2 or surgical masks explicitly do not provide adequate protection. Work should not be carried out against the wind, and other people should not be present in the vapor area.
Common mistakes are treating colonies that are not broodless, using unapproved vaporizers or other oxalic acid products, and using technical-grade oxalic acid from chemical suppliers. The latter is not permitted: organic acids may only be applied to bees as approved veterinary medicinal products; neither beekeepers nor veterinarians may obtain them from chemical suppliers. The application must be documented in the Colony Register. For honey, the information in the respective package leaflet applies; as a general rule, treatment is carried out after the last honey harvest.
Quellen (4)
- BVL: Hinweise zur Anwendung des Tierarzneimittels Varroxal 0,71 g/g Pulver für den Bienenstock in Bezug auf die geeigneten Verdampfer (15.03.2024)
- LAVES Institut für Bienenkunde Celle: Was man über Varroxal, das bislang einzige zugelassene Varroazid zum Verdampfen, wissen sollte
- LWG Veitshöchheim: Merkblatt Varroa 3, Medikamentöse Standardverfahren
- Emmerich, I.: Zugelassene Arzneimittel für Honigbienen in Deutschland, Berliner und Münchener Tierärztliche Wochenschrift 2018