Re: These misterous bees
calbee, i notice your join date is 2011. is this colony in it's third year? do you know how to identify mite frass on the brood combs? sounds like a generous offer from jrg13, why not take him up on it?
unless you have performed a proper test for mites and/or examined the brood combs there is really no way you can rule them out. i agree with the others that mites are at the top of the list of suspects.
sorry about your bees.
journaling the growth of a treatment free apiary started in 2010. 20+/- hives