Thymol
Behandlungsmittel
Thymol is a phenolic substance that occurs naturally in the essential oil of thyme and a number of other flowering plants.
Thymol is a phenolic substance that occurs naturally in the essential oil of thyme and a number of other flowering plants. In beekeeping it is placed in the colony in carriers such as gel, wafers, or strips, from which the active substance slowly sublimates into the hive air. The exact mode of action is not fully understood. It is assumed that thymol disrupts the mites' olfactory orientation and, above a certain concentration in the hive air, acts directly lethally via protein denaturation.
Thymol only reaches mites sitting freely on the bees, not those in the capped brood. An effect on brood mites arises only indirectly, as the mites that leave the cell with the hatching bees are gradually killed over the long treatment period. The effect sets in with a delay and reaches its maximum only two to three weeks after the start of treatment. Thymol is therefore unsuitable for rapidly reducing mite levels in heavily infested colonies.
Efficacy depends heavily on outdoor temperature. About 20 to 25 °C is optimal. Below 15 °C too little active substance sublimates and the treatment becomes insufficient. At daily maximum temperatures above 30 °C, stress and mortality of bees and brood increase noticeably. The bee institutes name further restrictions: treatment should start by mid-July at the latest, the colonies must have been cleared of supers and given an initial feeding, and feeding is barely possible during the several-week treatment. Where there is a risk of robbing, thymol should be avoided.
Typical problems include starting treatment too late, continuing to feed during treatment, propolization of the carriers, and use in forest honeydew areas, where the institutes explicitly do not recommend thymol. Because the persistent thymol odor bothers the bees, brood near the carriers can be removed by the colony. Natural mite drop is no longer meaningful during a thymol treatment; infestation can then only be determined via bee samples. A subsequent winter treatment with oxalic acid in the broodless state is required in every case.
Thymol-based products are approved as veterinary medicinal products and are available without prescription. The withdrawal period for honey is zero days, provided they are not used before or during the nectar flow. The residue aspect is important: thymol is fat-soluble and accumulates in the wax, from which it passes into the honey in a linear relationship. No honey may therefore be harvested from combs that were in the colony during treatment. When handling it, direct skin and eye contact should be avoided; thymol can trigger contact eczema.
Quellen (4)
- Emmerich, I.: Zugelassene Arzneimittel für Honigbienen in Deutschland, Berliner und Münchener Tierärztliche Wochenschrift 2018
- Landesanstalt für Bienenkunde Hohenheim: Hinweise zur Anwendung von Thymolpräparaten
- LLH Bieneninstitut Kirchhain: Infoblatt Varroazide
- LWG Veitshöchheim: Bayerisches Varroabehandlungskonzept, Medikamentöse Standardverfahren