Jerry: There is circumstantial evidence that mites lose host preference (read
availability) to young bees in the fall. Giordani found mites all over the bee,
eggs too, and Sachs reports that the chelicerae are strong enough to go through
the chitin in the thorax.  Maybe they only need the trahcea to lay eggs in, and
can (overwinter??) externally.
 
Just a thought, and some gleanings from the articles I've read.
 
diana