>
> >the mites 'piled into' the capped brood and escaped oxalic treatment?  I
> know theres no definitive answer from the group, but wondering if there is
> a known limit to how many mites will invade a brood cell, if there is a
> limited amount of brood.


They could certainly pile into a brood cell.  But that pupa would then
die.  Unless the bees had strong hygienic behavior and quickly uncapped
that cell, the mites would also die inside.  In any case, they would be
unsuccessful at reproduction.

I just spent some time doing more intense modeling of the mite numbers in
my breeding program, and came to the realization that I was overlooking
something.  I made the error of assuming that all the nucs that I make each
spring start with enough mites to gauge their  degree of mite resistance
via alcohol washes over the course of the season.  My deeper modeling
indicates that this is not necessarily the case.

A problem arises if the oxalic treatment that I apply to the nucs in April
is highly efficacious.  If I reduce the starting mite population in an
April nuc to 20 mites or less (total), then that colony will exhibit very
low mite wash counts all season long, clear through the next spring.  I am
observing this as I take my 11-month mite washes, in which only a handful
of colonies were able to hold their mites in check (although I've still got
three colonies exhibiting mite washes of zero after nearly a full year
without treatment).

The bottom line is that if a colony starts with less than 25 total mites in
spring, and experiences less than a 500-mite immigration over the course of
the season, it would by alcohol wash assessment erroneously appear to be
"resistant," although the true reason was that it simply didn't start with
enough mites to determine whether it was truly resistant or not.

Charlie has questioned the degree to which immigration is related to the
fall mite spike.  My revised modeling suggests that part of the spike that
I'm seeing is due to the low starting mite population, but it would still
take a lot of immigration in my operation to obtain the high spikes that I
observed.


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

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