I had read in (I believe) the American Bee Journal that varroa don't
only live on honeybees, but that they also can live on other insects
in the area, such as Bumblebees. Due to differences in incubation periods,
the bumblebees don't die off, and so the varroa are merely a pesky
parasite to them. If memory serves, didn't varroa originate in
India, where the incubation period for the Indian honeybee wasn't
as long, thereby making varroa only a parasite there, too?
 Since I'm a newbie to the list- if this type of unsubstantiated
general recollection is inappropriate, please let me know.
 Phil Wood
 Univ. of Mo=Columbia