Again I used the sticky board to count the mites in my hive. The last time I did this was in June, and back then, after the requisite 3 days of waiting I counted 30 mites.
This time I found 68. The threshold – the point at which you need to consider treatment – is a “mite fall” (the amount of mites that fall onto the sticky board as the bees grooms themselves) of 40-50 a day. So we’re still good. I don’t think I’ll do a treatment for varroa destructor. Their populations dwindle in the Fall and throughout Winter anyway. First of all, the queen stops laying eggs and that’s where the mites prefer to hang out, in the capped cells of brood where they can suck to their delight. Secondly, mites can’t stand the cold.
The brood population and the thermoregulation of the nest are related. The queen stops laying eggs in the Fall, and during the broodless period a colony will maintain a surface temperature of around 10 degrees C, just a few degrees above the honeybee’s chill-coma threshold, and 18 degrees C at the core. They only start warming up around the winter solstice, to around 34 C, when the queen starts laying eggs again. (*)
But then there’s the tracheal mite to consider. This sucker usually thrives throughout winter. I’ll have to do some research.
(*) I am reading Honeybee Ecology, by Thomas Seeley, a wonderful book that I most heartily recommend. It’s an academic (but) highly readable book. It’s not about practical beekeeping but the information it provides makes the practice of beekeeping much more transparent.