Bob said:

>  Looking back I suspect nosema ceranae played a big part. Because the
> problems were in late summer and fall none of use suspected nosema. We did
> not know nosema ceranae was in the U.S. Our samples did show three virus.


Bob, I also keep N ceranae high on my suspect list, as a potential accessory
to the crime.  What is important to understand, is that neither varroa,
tracheal mite, nor either species of nosema are likely to kill a healthy
colony unaided.  Rather, these parasites both stress the bees, and allow
proliferation of various viruses, which then kill the colony.  The effect is
amplified in times of poor nutrition, or with bees especially lacking in
certain genetic immune components specific for certain pathogens.

Recent research in bee viruses is likely to discover viruses that we did not
previously know existed in this country, which may well act synergistically
with nosema, varroa, and/or other viruses within the bee.

As you wisely stated recently, the immediate practical advice to beekeepers
would be to control the parasites, which would then help to control viral
replication.  However, a better understanding of the viruses, and the bees'
immune and/or genetic response to them may also be of great value to
beekeepers.

Randy Oliver

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