Wash Method (Mite Count)
Lexikon
The alcohol wash, also called the washing method, is considered particularly accurate among the common methods for determining Varroa infestation.
The alcohol wash, also called the washing method, is considered particularly accurate among the common methods for determining Varroa infestation. A sample of about 300 bees, which corresponds to roughly 30 grams, is taken from a brood comb, preferably one with open brood, killed immediately, and then shaken vigorously in a container with alcohol or a detergent solution. The liquid is then poured through a double sieve, and the detached Varroa mites are caught in the finer sieve, where they can be counted.
Because the bees in the sample are killed in this method, the alcohol wash is more invasive than the powdered sugar method, but it is considered much more reliable, even at low infestation levels, because hardly any mites remain stuck to the bees' bodies or are distorted by moisture. In the literature it is therefore often described as a kind of gold standard among the direct sampling methods.
For evaluation, the number of mites counted is related to a standard quantity of bees; it is usually given as mites per ten grams of bees. Since a hundred bees weigh about ten grams on average, this value can be read directly as a rough approximation of the percentage infestation of the sampled bees.
A common mistake in practice is to take the sample not from a brood comb but from a pure food or honey comb, where considerably fewer mites are present than in the brood area, so that the colony's actual infestation is underestimated. Equally important is killing the sample bees quickly and completely, since otherwise individual mites can leave the sample before it is counted.