Dear Dr.Moller
Perhaps the following references will be of use to you.
 
Gary,N.E. & Page,R.E.(1989).  Tracheal Mite (Acari:Tarsonemidae) Infestation
             Effects on Foraging and Survivorship of Honey Bees (Hymenoptera:
             Aidae).    J.Econ.Entomol.   82(3):734-739
 
Danka,R.G., Rinderer,T.E., Hellmich II,R.L. & Collins,A.M.  (1986)
             Foraging population sizes of Africanized and European Honey Bee
             (Apis mellifera L.) colonies.    Apidologie 17(3):193-202.
 
 
Both papers describe how the authors looked at foraging bees.  And in the
latter paper, the methodology of actually sampling the foraging population
is outlined.
 
Perhaps (albeit crude) you could try and simply move the original hive, whose
foraging population you wish to sample, some two feet away from the original
hive site, and replace it with another identical hive on the same spot.
Into the substituted hive, place stores.  I have been told that this is a
 simpleway of looking at the number of bees leaving the hive.
 
Peter Bowen-Walker  [log in to unmask]