Hello,
Are you SURE nosema killed your colonies?  Nosema weakens colonies but rarely
kills them.  What makes you think it was nosema?  When did you find them dead?
What did you observe in the colonies?  When is the last time you inspected
them to see their condition?  What was their condition then?  Have you still
got some of the dead bees?

It is estimated that about 60% of all the colonies in the U. S. have some
degree of
nosema, particularly those that have been confined for long periods of winter
without having 1, 2, or 3 days to make cleansing flights.  VERY FEW beekeepers
feed Fumidil-B because it generally DOES NOT KILL.  I don't take chances, I
feed Fumidil-B in late October and early November every year and have for
perhaps 30
years, and have never had nosema in my 100+ colonies; and I advise all
beekeepers to feed Fumidil-B since a feeding only costs about $2/colony, but
most ignore my
recommendations.  My bees are always alive and ready to work.  I am reminded
that
I can't do very good work or very much work when I have a case of diarrhea,
and I figure that "neither can a bee", so they get Fumidil-B every year.

Answer some of my questions, and I might be able to help you; but I doubt that
nosema killed your colonies.  The great majority of the time bees that are
sick from
something else and hence are weakened by that malady, get a normal touch of
nosema and die, not from nosema, but from whatever weakened them first.

By the way, what state are you in?

George Imirie
EAS Certified Master Beekeeper
Beginning my 69th year of beekeeping in Maryland
Author of George'e PINK PAGES