>Unlike with varroa, African bees, etc, we have no idea how or when this
"invasion" occurred.

Actually, we know that it happened in many areas by 2006, in some areas as
early as 1995, but hadn't reached a number of areas by 2010.  Perhaps the
best evidence of recent invasion, at least in Western Europe, is that of
Botias (2012), who analyzed some 240 frozen samples of honey dating back to
1988. The found that  "The first honey sample
in which N. ceranae was detected dates back to the year 2000."

The above, plus the data from the Bee Disease Lab, make a strong
circumstantial case for a fairly recent introduction, and an epidemic
beginning around the year 2000 in the U.S.  The epidemic appears to me to
have peaked in both Spain and the U.S. before 2010.

 >N. ceranae may have been widespread but undetected for decades, and
became prevalent as an opportunistic infection due to stressors such as
varroa, virus, or pesticides (or all of these). Correct me if I am wrong

The above is plausible, but I have reason to doubt that it is due to varroa
(studies have not found a correlation) or to pesticides (my bees are rarely
exposed to pesticides, but have plenty of N ceranae).  On the other hand,
the virus/nosema link is more plausible.  The data from the recent Monsanto
trial should answer that question.

--
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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