Mites in capped brood cells escape exposure until they emerge from the cell with the adult bee. Residues - fluvalinate mixes with oils and waxes. Leaving strips in over winter might result in a build up of residues in the wax. Resistance - mites are not equally susceptible to fluvalinate. Some strong hives may need three strips, some weak hives will only need one.
Place strips down between the frames so that they contact each side of the cluster.
The average hive will likely need two. No , with one exception. There is no sure way of knowing if enough fluvalinate remains in a strip to guarantee that it will work a second time. Store strips in a cool, dry and dark location wrapped in aluminum foil in an air-tight bag. Avoid direct sunlight.