I attended a lecture on forensic entomology some weeks ago. One of the
points that the speaker made was that the rate at which eggs hatch and
larvae mature is dependent on temperature. If the brood is held at a
slightly higher temperature (not high enough to be lethal to either bees
or mites) the shortened time for the bee to mature and leave the cell
might not be long enough for the mites to reproduce.

                                                Best regards

                                                Donald Aitken