Hi,
     Sounds like an interesting project. As far as I know, most Bombus
queens [the species in this region anyway] make their nest selections
in the spring after emerging from their overwintering burrows in which
they remained in diapause (sp?) after mating in the fall. I've found
several areas where many tens or up to a couple of hundred queens were
emerging from a patch of ground only 3 to 4 meters in diameter. I think
it would also be intresting to find out how/why these locations are
selected in the fall after the queens have been mated.
     I have some sources which I could forward if you are interested.
Unfortunately they are at home but it would be no trouble to dig them
up. I will post them along within the next few days.
 
                                       Cheers
                                              Brooke M. Oland
                                              Plant Industry Branch,
                                              Harlow Institute,
                                              N.S.D.A.M.,Truro,N.S.