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Integrated anti Varroa Treatment using Oxalic Acid and Thymol

By Klaus Klebs

Translated from the Schweizerische Bienen Zeitung 5/2004, page 18 by A.E.McArthur MIL


My anti Varroa Management System consists of a short period thymol treatment carried out in Spring using a thymol impregnated kitchen sponge. This procedure is followed by queen rearing, nucleus formation and shook swarm formation. From summer to autumn a series of titleernating procedures is carried out using the thymol impregnated sponge and oxalic acid fumigation with the VarrEX sublimator.

My anti Varroa procedures are  based on the following principles:

Production of Thymol Sponges

It is known that oxalic acid fumigation does not kill mites in the sealed cells, for this reason I decided last year to use essential oils – especially thymol which possesses varroicidal or disorientation properties, against the mite.

Measures taken in 2003

The thymol sponges were placed under the crown board behind the brood and left in place for 18 days. These sponges were removed 14 days before to the first supers were placed.

During the summer after feeding when no supers were on the hives I fumigated twice with oxalic acid and subsequently carried out another 2 treatments using the thymol sponges. The thymol sponges are not used in the colony during feeding since this may encourage robbing.


The Varroa drop in the test colonies, which had 12 – 14 combs was not particularly heavy. After the insertion of the thymol sponges the daily mite drop increased and then stabilised. A subsequent oxalic acid fumigation treatment did not result in an increased mite drop.

During 2003 in the 12 test colonies which were checked every day after a thymol application and a subsequent oxalic acid treatment only 100 mites dropped, this was significantly less than in previous years.

Method of Treatment

I carry out a triple thymol sponge treatment (in the Spring for three weeks, 14 days before the nectar flow; then after the honey harvest and feeding, I apply the thymol sponge again twice over two four week periods) as well as two oxalic acid fumigations in late summer and then again 3 weeks after the first frost to remove the residual phoretic mites.

Thymol Sponge

The application of the thymol sponge has shown a good result. The sponge is placed under the crown board. Applies from above gives a better disrtibution of the vapour. In the spring I reduce the mite populations by carrying out a 3 week long thymol treatment. Due to the danger of thymol contamination of the honey the sponge is removed 14 days before the supers are added. Thymol is wax soluble but evaporates relatively quickly. A heavy thymol dose causes a reduction in brood rearing. The sponge should not be placed close to the entrance due to the danger of starting robbing.

In contrast to earlier years, in 2003 no significant drone sacrifice was carried out in order not to disturb the colony harmony and to achieve optimum queen mating at the mating station in my vicinity.

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