The Varroa mite is common and numerous in bee colonies in worldwide. The Varroa mite has been observed in bee colonies in Europe and the USA since the end of the 19th century. According to various reports, the only country in the world where the Varroa mite does not occur is Australia. See the section Pollen and microbial diversity of this website for an explanation of this phenomenon. Other mites are found in bee colonies besides the Varroa mite. Over time, the Varroa mite has become the dominant mite species in bees.
Winter mortality and Varroa
The brochure ‘Effectieve bestrijding van varroa’ [Effective Varroa control] (WageningenUniversity, 2010) states the following: “In most cases, winter mortality of honey bees is attributable to this disease.”
The thought that Varroa is responsible for the high bee decline and winter mortality is inaccurate, and therefore incorrect. A bee colony can thrive in the presence of the Varroa mite. Since about 1980, bee decline and winter mortality have been limited to a maximum of 15%, despite the presence of Varroa mite.
A key question, that the scientific institutions have never posed, is why the Varroa mite is present in the first place, why it has been able to establish itself and become dominant. That this has crossed over from the Asiatic honeybee Apis ceranae to the European honeybee Apis mellifera may perhaps be true. The factors that ensure the Varroa mite thrives in many parts of the world, particularly in Europe and the USA, have not been traced. It is generally considered that the tropical honeybee is more resistant to the Varroa mite. However, the basis for this resistance mechanism is unclear and is not explicitly documented.
Varroa and viruses
The currently high bee decline and winter mortality in relationship with the Varroa mite is attributed to the viruses which the mites supposedly carry and with which they infect the bees. The presence of viruses in mites has been shown, as well as the fact that these can also infect bees. Why the quantities of these viruses in bees has subsequently substantially increased remains, to this day, unclear. This may be related to the weakened immune system in the bees. The virulence characteristics of the viruses are more important than the infection itself. The viruses are always present.
Varroa infection is controlled with organic acids and thymol, as well as with Amitraz. As explained in the section How formic acid, oxalic acid and thymol work of this website, the effect of formic acid, oxalic acid and thymol relies on a change in the microbial system. How Amitraz works is explained in the Amitraz section of this website.
Why is Varroa mite present in bees?
The presence of the Varroa mite in bee colonies can be explained with the model of microbial competition. In other words, a bacterium that the mite carries thrives in more alkaline conditions. The role of the viruses is, at the most, incidental.