Wash Method (Mite Count)
Lexikon
The wash method, also called the alcohol wash, is regarded as particularly accurate among the common procedures for determining varroa infestation.
The wash method, also called the alcohol wash, is regarded as particularly accurate among the common procedures for determining varroa infestation. A sample of about 300 bees, roughly equivalent to 30 grams, is taken from an open brood comb if possible, killed immediately, and then shaken vigorously in a container with alcohol or a dish soap solution. The liquid is then poured through a double sieve; the dislodged varroa mites remain in the finer sieve and can be counted.
Because the sampled bees are killed in this procedure, the wash method is more invasive than the powdered sugar method, but is considered significantly more reliable, even at low infestation levels, because hardly any mites remain stuck to the bees' bodies or get skewed by moisture. In the literature it is therefore often described as a kind of gold standard among direct sampling methods.
For evaluation, the counted number of mites is related to a standard quantity of bees; it is common to state it as mites per ten grams of bees. Since one hundred bees weigh about ten grams on average, this figure can be read directly as a rough approximation of the percentage infestation level of the sampled bees.
A common mistake in practice is taking the sample not from a brood comb but from a pure food or honey comb, where far fewer mites are found than in the brood area, which underestimates the colony's actual infestation. Equally important is killing the sample bees quickly and completely, since otherwise individual mites can leave the sample before it is counted.