Finished dusting four hives with powdered sugar on Saturday.
I'll put the sticky boards down next Friday, and pull them Sunday. That's when I'll do another mite count.
The combination of powder and a screened bottom board is part of a natural program of preventative maintenance. I've got two hives I treated with Apiguard--- they had a high varroa infestation, so I went to a stronger treatment (thymol, an essential oil), after which I'll dust them.
All an effort to avoid using Apistan or other pesticides that mites across the world are already becoming resistant to.
There is controversy over the efficacy of the powdered sugar treatment. This link http://www.ibra.org.uk/articles/20090217_5 is a summary of a study which says it's pretty much useless.
However, beekeepers everywhere use this--- again, not as a cure-all, but as a part of an overall mite control program. The goal isn't eradication, the goal is to help the bees cope with a manageable number of mites. In the end, the real solution will be mite-resistant bees--- there are a number of breeding programs underway towards that end.
Anyway, I promised to show, not tell... so here's a video demo of the Powdered Sugar method.