In case you missed this: varroa kills hives & infects your neighbors' hives. If you have not yet tested your hives it's important to do that now!
Please see below for info on how to test.
If you've tested and need to treat, MAQS strips (formic acid treatment) are available now.
This is the method we like best. A 72-hour (three-day) dropcount is the standard.
At this season, if your count is 10 or more over 72 hours you need to treat.
If you use a screened bottom board, it's very simple to test and it doesn't disturb the honey bees at all.
Cut a piece of white plastic or cardboard poster board that will slide beneath your bottom board without scraping. Before you place it, spray it with Pam to make it sticky.
Time your test. When time is up, pull the board out carefully so the debris stays in place and is not scraped off, and count your bee mites. You can tell a varroa mite from a bit of pollen or wax by squashing with a fingernail - bee mites won't crush so easily.
If you don't have time to use the sticky board, powdered sugar roll is the other benign test. You get a quick answer, but the bees you use will be shaken up a lot. Info sheet on sugar roll test method here.
Note that powdered sugar is good for testing but not for treatment -- see discussion below.
You can observe varroa in capped drone cells by opening a cell and looking for a brick-red mite on white drone pupa. Presence of mites is an indicator of infestation, but not a reliable way to measure.
Formic acid treatment is effective. It is well-supported in the scientific literature, and also recommended under biodynamic regimes. It kills mites inside capped cells as well as those on adult bees. It also kills tracheal mite. Formic acid is naturally found in honey. You can even treat with honey supers on if need be. And it is registered for use in the USA.
For all these reasons, it is the treatment of choice for us, especially at this time of year.
Many beekeepers prefer MAQS formic acid strips because they are easy and safe to use if you follow the instructions.
Application temperatures need to be between 50 and 92F so don't delay.
Our goal is to go being overwintering with young, healthy bees that can live until spring!
Regarding powdered sugar as a tool in varroa control, (as opposed to its use in testing), many people like the idea, but it is not effective: It has no impact on the 60% or so of the mites inside cells at any given time; even with repeated applications meant to address emerging mites, at least one significant study showed no impact on mite counts at all. Bottom line: It just won't save your bees' dying from varroa.
Varroa is one of the most serious threats to your bees, and you can do something about it: Test & treat.
Thanks to Jim Fischer for this article.