Varroosis (Varroa Mite)
Krankheiten
Varroosis is the disease of a bee colony caused by the mite Varroa destructor.
Varroosis is the disease of a 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 foundress mite crawls into the cell shortly before capping and lays eggs there, and the developing mites feed on the pupa. Drone brood is clearly preferred because it stays capped longer and allows the mites more offspring.
In the colony, a heavy infestation shows up as damaged young bees with crippled wings or a shortened abdomen, patchy brood, opened or sunken 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 deformed wing virus and weakens the bees, the collapse is often not the result of mite numbers alone but of the interplay of parasite and viral infection. A collapse in late summer or autumn is typical, often accompanied by robbing by neighboring colonies.
The infestation can be measured instead of 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 sample of bees is dusted with dry powdered sugar and the mites that fall off are counted. Opening capped drone brood also gives an indication. The thresholds above which treatment is necessary depend on the month and region, so you should follow the treatment concept of the responsible bee institute and record the figures.
Control is a year-round concept, not a single measure. In spring and early summer, removing drone brood reduces the infestation. After the last honey harvest comes the summer treatment, often with formic acid using a suitable evaporator, or with methods based on brood removal or on splitting and treating. In winter, when the colony is broodless, the remaining mites are removed with oxalic acid by trickling or vaporizing with a product approved for this purpose. Every treatment must be followed by a check of its success via the mite drop.
Treatments during the nectar flow or with a honey super in place, homemade mixtures, and unapproved products are to be avoided. Only veterinary medicines approved for bees may be used, and every application must be recorded in the colony register. Anyone who postpones the summer treatment harms the winter bees that are raised in August and September. In Germany, varroosis has been notifiable since 11 March 2026 under the Animal Disease Reporting Ordinance (Annex 2), but with considerably more limited consequences than American foulbrood. In addition, there is the general obligation to keep one's own colonies healthy.