The principal behind talcum powder treatment is that you dust the
bees fairly thoroughly with talc (plain unscented) and in grooming
themselves to get rid of the talc, they also pull off the mites
living on their body surfaces.  One problem is that the mites are
often left alive so they may be able to crawl back up into the hive
and reparasitise bees, with little effective reduction in numbers
having been achieved. I have seen this in a number of books but it
isn't used by anyone I know personally. Andrew.