The Varroa mite(Varroa destructor) originates from Asia and parasitizes bees and bee brood. It reproduces in the bee brood. In addition, it is a vector of various bee viruses. Both the parasitization and the transmitted viruses damage bees and brood stages. It has been present in Austria since about 1980 and is now found in every bee colony. It is an important trigger of colony collapses and is associated with high winter losses.

In Asia, the varroa mite lives in colonies of the Eastern honey bee(Apis cerana). In the course of evolution, these bees have developed effective defense mechanisms to keep varroa infestation low. Therefore, infested colonies of this bee species do not perish from varroa mite. In the last century, Western honey bees(Apis mellifera) were brought to Asia by humans and thus came into contact with the varroa mite. As a result, the mite was able to use the Western honey bee as a host as well, and spread almost all over the world. Currently, the varroa mite is found in Asia, Europe, Africa, North and South America.

Varroa mites are generally present in every bee colony. During the breeding season of the bees, the varroa mites multiply in the colony and thus become a serious problem. For reproduction, the Varroa females migrate into brood cells that are ready for mating. The complete development from egg laying to mating of the young females then takes place in the closed brood cell. During this time, both the mother mite and the offspring feed on the bodily fluids of the bee larva. With the hatching young bee, the mature, already mated Varroa females also leave the brood cell and transfer to other bees. Thus, a new cycle begins again.

The number of female offspring per reproductive cycle is different in worker and drone brood. In worker brood, one to two adult daughter mites are produced per mother mite, while in drone brood two to four daughter mites are produced due to the longer mating period. This can lead to high infestation numbers and the development of varroosis symptoms in the course of the season.

Infestation of bee brood has the greatest impact on the health of the colony, as the brood is damaged by the mites in the course of its development (withdrawal of nutrients from the bee larvae, transmission of viruses). Infected bee larvae give rise to damaged young bees with shortened lifespan, crippling and reduced performance.

Varroosis is the symptom pattern that occurs in colonies of the Western honey bee in the course of a massive varroa infestation - usually in combination with virus infestation. The symptoms affect both the adult bees and the brood. Only when there is already severe damage to bees and brood, the symptoms of varroasis become obvious. However, even if the colony looks strong and healthy at first glance, a dangerously high number of varroa mites may already be present.

Typical signs of a colony with varroosis are bees with shortened, crippled wings, with shortened abdomens, varroa mites visible on bees and combs, and a patchy brood nest. Colonies dead from varroosis were typically strong until recently and were producing abundant honey. Now, either the hive is largely empty of bees or there are still large quantities of dead bees in the bottom board. On the combs are capped, not hatched brood cells, which usually contain large amounts of mites. Often there are several mites in one brood cell. Usually there are also abundant honey and pollen stores. Such colony collapses usually occur in late summer, fall and winter.

To get the varroa mite under control, an integrated concept of varroa control is required. This must be planned and coordinated with the farm. It consists of a combination of successive measures to reduce infestation over the course of the year. The measures have to be adapted to the seasons, the period of the grape harvest, the state of the colony and the type of operation (conventional or organic beekeeping). For details on the integrated concept of varroa control, please refer to the technical information below and the PDFs in the download area.

All methods of varroa control that stop or slow down the growth of the varroa population in the colony serve to prevent varroasis. Particularly worthy of mention here are the biotechnical methods that do not involve the use of veterinary medicines. These methods can also be used during the breeding period, when veterinary medicines may not yet be used. Their effectiveness is based on the fact that in colonies with brood, the majority of varroa mites are found in the capped brood cells. If this brood is partially or completely removed from the colony, the mites in it are also removed. This delays the development of a critical varroa infestation. For details on biotechnical methods, please refer to the technical information below and the PDFs in the download section.

Another prevention strategy is breeding varroa tolerant bees. Breeding aims to select colonies that are themselves capable of limiting Varroa mite infestation to such an extent that no, or reduced, additional control measures are required. In the existing bee population, those colonies are identified that are more resistant to the mite due to their genetic characteristics. These colonies have the ability to remain healthy and productive despite Varroa mite infestation. Information on this can be found in the folder "Varroa mite - selection for varroa tolerance" in the download area.

The Varroa mite has been present in Austria since about 1980 and can now be found in every bee colony. According to the new EU Animal Health Law (AHL), infestation with Varroa spp. (varroosis) is notifiable. Analogous to the previous regulation, it is planned that notification will only be mandatory in the case of epidemic occurrence of varroosis. Details are currently being worked out (as of January 2021).