>4.45 million spores per bee is a serious infection

Hi Jason.  It depends.  Here in Calif, a springtime count of 5M from a
sample of foragers is nothing to worry about.  Even in autumn, going into a
cool winter (occasional snow, but flight nearly every week), I find
virtually no correlation between such a count in house bees, and subsequent
colony strength or survival.

But as Medhat (and Steve Pernal) point out, things will likely be different
if the bees are confined for the winter.

I currently suggest that any bee samples for nosema be taken from under the
cover or from an outside comb, which gives a more representative sample
than an entrance sample.  And the individual gut squash of 10 bees,
although closely correlated with a mass sample, gives more indication of
the actual impact of nosema upon the colony.

I'm trying to steer clear of Pete and Jim's tiff, but I have been in
continuous deep conversation with every major player involved with *Nosema
ceranae* since 2006.  I agree with Jose about the ambiguity and confusion
regarding nosema in general, and N. ceranae in particular.  Too many
conclusions have been drawn based upon too little field data.

I go back to Ingemar Fries, who long maintained that N apis was mainly a
problem for bees kept at the colder limits of their range.  I see only
slight differences between the effects of infection by either of these
"nosema cousins," although N ceranae is clearly better adapted to warmer
areas.  They both appear to be opportunistic pathogens, to which bees can
evolve (or be selected for) resistance.  And either can deliver the killing
blow to a colony stressed by other factors.

In general, I find that my strongest and best honey-producing colonies
rarely have more than 10% of the population infected with nosema (usually
zero).  On the other hand, my weaker or poorly-performing colonies may have
20% or more infected.  But since I do not find nosema levels to be a clear
predictor of colony performance, I strongly suspect that nosema is
opportunistic at going epidemic in colonies already stressed by something
else.  And then, due to positive feedback, the effect can snowball.  If
more than 50% of the bees in a colony become infected, this can snowball
into sudden colony depopulation.

There are still misconceptions floating around about nosema, such as it
causing dysentery.  If a colony suffers from dysentery from any cause (poor
food, yeasts, or nosema) and *also* has some bees infected with nosema,
then the dysentery certainly accelerates the transmission of the spores.
But dysentery doesn't equate with nosema.

Their prevalence and impact upon the colony appear to be closely
intertwined with colony nutrition.  Well-fed bees live longer, and appear
to better tolerate an infection by nosema, and may thrive despite
alarmingly high spore counts.  In warm areas, colonies tend to purge nosema
in summer (although I continue to hear reports of high levels of infection
during summer in some areas--I do not understand why).

I strongly suspect, as does Jerry, that nosema is far more of a problem if
the bees are already immunologically stressed by chilling, poor nutrition,
and viruses.  Similar to Juanse, I now focus upon dealing with those
factors, rather than worrying about nosema.

I have worked with several commercial beekeepers who came to the conclusion
that too much fumagillin was hurting their hives more than helping them,
but this was in warm areas.  There is plenty of older research indicating
that treatment with fumagillin at appropriate times may benefit colonies in
cold-winter areas (and some unpublished research of my own that suggested
the same during the CCD epidemic).

In summary, we still have a poor understanding of N ceranae.  It rapidly
invaded the U.S. between 2001 and 2010, and as expected with the invasion
of a novel parasite, likely had a strong impact during the initial invasion
wave (which corresponded temporally with the CCD epidemic, perhaps not
coincidentally). But in my California operation (and Juanse's in Chile) we
don't even worry about it any more.

Why it still appears to be an occasional issue in other areas remains to be
determined, and could well be related to the stocks of bees kept.  As I've
previously written, I consider nosema to be a "smoldering epidemic"--always
there, but requiring some other stressor to flare up enough to knock out a
colony.


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

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