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Calculating varroa mites per thousand bees

Homemade sticky boardsIf you want to monitor the varroa mite levels in your bee hives, it's a good idea to take counts at multiple times rather than using one snapshot to assess the long term health of your hive.  So I repeated my three day stickyboard counts this week.  To refresh your  memories, the mother hive dropped 44 varroa mites per day in mid September while the daughter hive dropped 12 per day.

My new count showed nearly the same mite fall for the mother hive --- 41 mites per day --- but it seemed like the varroa mite population in the daughter have had undergone a population explosion.  This time, the daughter hive dropped 200 total mites, or 67 per day!

An increasing varroa mite population in the autumn is bad news, but I decided to get a bit more scientific before I started to worry.  Mite fall is a problematic way to monitor varroa mites since a large population of bees will naturally drop many more mites than a small population of bees.  The way to deal with this error is to estimate how many bees are currently in your hive and calculate mite fall per thousand bees per day.

Estimating bees per frameNo, I didn't sit in front of the hive and count heads all day long.  Instead, I looked through both hives, counting how many frames (or portions of frames) were covered with bees.  A deep frame completely covered with bees on both sides holds roughly 2,000 workers, so I was able to come up with population estimates for both hives.

Remember how I started feeding the daughter hive a few weeks ago since I was concerned that she was going into winter with too few honey stores?  One of the troubles with fall feeding is that it can prompt the queen to lay lots of eggs at a time of year when the hive doesn't need that many workers.  The mother hive --- not fed, so changing her population based on the natural ebb of the seasons --- had roughly 9,500 bees in the hive.  On the other hand, the daughter hive had bulked up drastically and now housed 18,250 bees!

Brood from fall feedingThe good news is that when you divide the mite fall figures by the population of each hive, it turns out that the daughter hive is in fine shape.  The mother had roughly 4.3 varroa mites fall per thousand bees per day during my test while the daughter had 3.7 mites per thousand bees per day.  Given all of the wiggle room in my measurements, I'd say mite populations in each hive are roughly equal on a per bee basis.

The bad news is that the daughter hive has way too many workers in it!  She has put away the 22 pounds of sugar I gave her and now has 48 pounds of capped honey, but I'm a little concerned that the massive population of workers will eat right through it before winter comes.  Hopefully once the unnatural "nectar flow" disappears, the hive will kick out those extra workers ASAP.

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Good info, as always.

I'm curious to how you would have treated for varroa if you had discovered that the hives were overrun with varroa.

Comment by Greg S Fri Oct 7 09:55:18 2011
That's an excellent question, and one I was pondering seriously when I thought the daughter hive was overrun. Mainstream beekeepers put in chemical strips at this time of year to kill varroa mites, but I obviously want to avoid that. I made a post last winter about treating varroa mites organically. A lot of the tips in that post I already use as a matter of course, but if I needed to take a quick dent out of their population, I'd probably try smoking with black walnut leaves, dusting with confectioner's sugar, or using thyme or mint in the hive.
Comment by anna Fri Oct 7 15:00:18 2011

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