Infestation Level
Lexikon
The infestation level describes how heavily a colony is affected by the varroa mite at a given point in time, usually expressed as the ratio of the number of mites to the number of sampled bees, or as the daily natural mite drop.
The infestation level describes how heavily a colony is affected by the varroa mite at a given point in time, usually expressed as the ratio of the number of mites to the number of sampled bees, or as the daily natural mite drop. It is therefore the central measure that beekeepers use to decide whether and when a treatment becomes necessary.
The infestation level is determined through various procedures, each of which intervenes in the colony to a different degree: the powdered sugar method and the wash method give a snapshot from a sample of living bees, while evaluating the natural mite drop via the varroa board estimates the infestation level indirectly, from the number of dead mites that fall by themselves. Because all three procedures only capture a slice of what is happening in the colony, and the mites are not evenly distributed within it, each individual measurement always provides only an approximation of the true overall infestation.
What matters especially for interpretation is that the infestation level considered critical shifts markedly over the course of the year. During the brood-intensive season, the mite reproduces heavily within the capped brood, so an infestation level that would still be harmless in early summer can already be much higher just a few weeks later. In broodless phases in winter, by contrast, even a comparatively low natural mite drop is regarded as a warning sign, because hardly any young mites are then growing up hidden in the brood, and each dead mite makes up a larger share of the total population.
A common mistake is to assess a single measured infestation level without reference to the season, or to directly compare values from different measurement methods. Because the wash method, the powdered sugar method, and evaluating the varroa board each capture a different slice of what is happening in the colony, their results are only interchangeable to a limited extent and should, when in doubt, be interpreted together with the recommendations of the bee institutes.