Re the invasion of N ceranae, a question was raised to me as to why it took
a while for it to go epidemic after its original invasion.  This is
actually not unusual.  The same happened with varroa in Asia, and with DWV
everywhere that varroa went.  The original parasite was not well adapted to
the novel host, and needed to evolve to fully exploit the host population.

It appears that it may take some years for enough mutation, gene swapping,
and natural selection to occur for a novel parasite to become virulent
enough to initiate a true epidemic.  Then the epidemic runs its course,
either exterminating the host, or the host coevolves enough resistance
mechanisms that the parasite becomes relatively benign, other than brief
flare ups either during stress or when a mutation occurs.

In my own operation, it appeared that N ceranae may have peaked in the
2005-2010 period, and is now becoming less of a problem.  This also
happened (earlier) with chalkbrood, tracheal mite, and possibly AFB.  On
the other hand, EFB is enjoying a resurgence.

Host/parasite relationships initially are not static.  I suspect that
particularly virulent strains of N ceranae were about in the early years of
this century, just as particularly virulent strains of IAPV were hammering
us at that time.  Both the RNA viruses and nosema are notable for rapid
evolution and genetic exchange, so we can likely expect dynamic
host/parasite adjustments from time to time.
--
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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