When I pulled the mite boards out last week, after three or four days in the hive, I counted 1 to 2 mites per square inch. These boards were put in just before the dusting. Surprisingly, the boards were not covered with powdered sugar.
I just basted now basted the boards in olive oil and slipped them into both hives at 7:15 PM tonight. We will see what the mite count looks like after three days with no powdered sugar.