Varroosis (Varroa Mite)
Krankheiten
Varroosis is the disease of a honey bee colony caused by the mite Varroa destructor.
Varroosis is the disease of a honey bee colony caused by the mite Varroa destructor. The mite originally comes from the Eastern honey bee Apis cerana and has spread worldwide to the Western honey bee since the 20th century. It reproduces exclusively in capped brood: the mother mite enters the cell shortly before capping, lays eggs there, and the developing mites feed on the pupa. Drone brood is markedly preferred because it stays capped longer and allows the mites more offspring.
In the colony, heavy infestation shows up as damaged young bees with crippled wings or a shortened abdomen, patchy brood, opened or sunken cell cappings, and mites sitting on adult bees. Brown, shield-shaped mites can be found in the debris on the bottom board insert. Because the mite also transmits viruses such as the deformed wing virus and weakens the bees, colony collapse is often not the result of mite numbers alone but of the interplay between the parasite and the viral infection. A collapse in late summer or autumn is typical, often combined with robbing by neighboring colonies.
Infestation can be measured rather than estimated. Common methods are debris diagnosis using a bottom board insert, in which the natural mite drop is counted over several days and converted into mites per day, and the powdered sugar method, in which a measured bee sample is dusted with dry powdered sugar and the falling mites are counted. Opening capped drone brood also provides clues. The threshold values above which treatment is required depend on the month and region, so beekeepers should follow the treatment concept of the responsible bee institute and document the figures.
Control is a concept spanning the whole year, not a single measure. In spring and early summer, removing drone brood reduces infestation. After the last honey harvest comes the summer treatment, often with formic acid via a suitable evaporator or through methods involving brood removal or splitting and treating. In winter, when the colony is broodless, the final mite treatment follows with oxalic acid, applied by trickling or vaporizing with a product approved for this purpose. A follow-up check on mite drop belongs after every treatment.
Treatments must not be applied during the nectar flow or with a honey super in place, and homemade mixtures and unauthorized products must not be used. Only veterinary medicinal products approved for bees may be used, and every application must be documented in the colony register (Bestandsbuch). Anyone who postpones the summer treatment damages the winter bees that are reared in August and September. There is no reporting requirement for varroosis in Germany, but there is a general obligation to keep one's own colonies healthy.