Joe wrote:  this study appears to have struck a great hole in the non 
virulent
theory.

This study certainly reaffirms the one unsolved aspect of varroa 
management--immigration from susceptible colonies.  But I don't know if I'd 
go so far as to say that it demolished the non virulent hypothesis.

In my area of California, robbing occurs any month of the year, and it would 
be extremely difficult to imagine nonvirulent mites evolving here, 
especially with the constant influx of managed bees.  However, I don't know 
if we can extrapolate the conditions in my area, nor in Germany, to short 
season, cold winter areas, where colonies don't collapse until after it's 
too cold to rob, such as on Gottland Island.  There's no reason that 
nonvirulent mites couldn't evolve there.  So I'm not sure that the theory is 
universally dead.

It's pretty obvious to me that it is far more probable for mite resistance 
and tolerance to evolve in the bee, especially since I see it happening 
(with the help of directed selection) in my own apiaries, and, in your feral 
colonies, Joe.

In the study cited, 12 colonies apparently picked up phoretic mites by 
robbing out 2 collapsing colonies, or a 16% loss of the entire bee 
population in the area during the short period of the study.  I'd be curious 
as to the rate of fall collapse in feral colonies in the Arnot forest, or in 
your area.  If a resistant colony picks up an extra 200 mites late in the 
fall, it may indeed be only a relatively moderate increase in infestation if 
they are already carrying say, 1000 mites at that time of year (a typical 
load for a mite-tolerant colony at that time of year).  If the colonies 
exhibit strong varroa sensitive hygiene and grooming behavior, they may well 
be able to tolerate that degree of influx.

Some 2000 mites were apparently picked up from two collapsing colonies--an 
average of 1000 mites per colony.  It would be of interest to model the 
dynamics of a feral population, as to what percentage of colonies could 
collapse while it's still warm enough to rob, what the infestation level at 
time of collapse was, the efficacy of transfer of the surviving mites, and 
the degree to which the receptor colonies were able to expel them.  The 
result of interest would be to maintain a stable population of colonies. 
Any modelers out there?

Randy Oliver 

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