If you’re doing an alcohol wash or sugar shake to count mites, you just divide the number of mites by the number of bees in the sample, then multiply by 100 to get the percentage of the hive with varroa infestation: e.g. (No. of mites / 300 bees) x 100 = % Infestation.

If you’re doing a sticky board count, you can follow some general guidelines to get a percentage: according to a CAPA paper on the economic threshold for varroa mites [PDF file] on the Canadian prairies, a natural mite drop of 33-34 in a 24-hour period is counted as 5-6% infestation. But there are different numbers for counts if you’ve used Apistan or Check-mite or formic acid to get the drop — they lay it all out in that paper, so it’s worth having a look.

The CAPA information about economic thresholds — what kind of varroa infestation the colonies can tolerate before the bees and honey production starts to suffer — is specific to the prairies and it’s different at the different seasons of year, but that should give you a starting point. And of course you’ll want to be putting in sticky boards to test throughout the season, so you have a good idea of whether your numbers of mites are going up or down from one test to the next, and how quickly!

Hope this helps.

Thank you