Edlinger’s Varroa Indicator
Work out the varroa mites in your colony
The number of varroa mites in a colony is a very important factor for the health and survival of a colony. With Edlinger’s varroa indicator, the number of varroa mites lying on the varroa tray can be projected onto the whole colony, giving you a better picture of where things stand.
The indicator is named after its developer. It was developed over a period of five years, during which many thousands of brood cells had to be opened and the varroa infestation counted.
Only three details matter: the day the mites on the tray were counted, how long ago the tray was last cleaned, and the number of mites found. From these, the indicator works out the approximate number of varroa mites in the colony and how many could be successfully controlled in a broodless state and in a colony with brood.
Result
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The assessment takes the month of the count into account: in spring and late autumn the same mite drop weighs more heavily than in May and June. The projected number of mites is not affected – all year round it is the daily drop times 333.
Mite drop and treatments in one place
You record counts and varroa treatments with date, product and quantity right at the apiary. Your treatment journal builds up along the way.
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The calculation goes back to the beekeeper Kurt Edlinger, who developed it over several years. It is described, among other places, in the German Wikipedia article Varroamilbe.
Frequently asked questions
When do I have to treat against varroa?
The indicator shows three levels: up to about 900 assessed mites nothing is needed, above that you should keep watching, and from around 1,100 you must treat. Assessed means the projected number, weighted by the month of the count.
Where do the thresholds and the factor 333 come from?
From Edlinger’s own method, which was developed over five years – many thousands of brood cells were opened and counted along the way. The calculator reproduces it unchanged: the daily mite drop times 333 gives the number of mites in the colony, weighted by a monthly factor between 0.9 in June and 1.8 in December.
It is a method in its own right and does not always match the damage thresholds of the bee institutes. Common recommendations put the limit at around one mite per day in May and June, and five to ten in July and August depending on the source. If you count in early summer, keep that in mind and follow the stricter figure when in doubt.
Why does the month of the count matter?
The same mite drop means something different depending on the time of year. In spring and late autumn it weighs more heavily than in May and June, when the colony is at its strongest. The number of mites shown stays the same – only the assessment shifts.
What does “treatable in a broodless colony” mean?
As long as there is brood, most of the mites sit in sealed cells and are protected from any treatment. In a broodless colony they sit on the bees and can be reached. The indicator uses fixed shares for this: around 80 per cent in a broodless state, around 20 per cent in a colony with brood. This is exactly what the winter treatment of the remaining mites is based on.
What is the difference between the two treatment lines and “of these, on the bees”?
The first two lines come from Edlinger’s method and state how many mites a treatment typically catches: around 80 per cent in a broodless state, around 20 per cent in a colony with brood. These are fixed shares, regardless of the state of your colony.
The third line says something else: where the mites are sitting right now. In a broodless colony practically all of them are on the bees and can be reached; as long as there is brood, the larger share is hidden in sealed cells. This line follows what you enter for the brood state and adds to the projection without changing it.