Problem:  evaluating varroa resistance by correlating mite populations
to honeybee populations w/o using a chemical treatment (which would skew
the population).
 
One solution:  At the U of Manitoba, varroa research programs have used
a shaking test, where a specific sized sample of bees is soaked in
Alchohol and shaken for 5 mins (on a mechanical agitator).  This process
dislodges the mites which fall to the bottom of the container, where
they can be collected and counted.  This will give you a mite/bee ratio
for the hive (w/o any test to the hive directly).  This test must be
corrected for the variations of mite and bee populations (i.e. Bee
populations naturally increase quickly at certain seasons, thus
appearing to reduce the mite/bee ratio).
 
Hope this helps, Phil.