> Small point, but the mites do not vector pathogens. 

They do vector viruses.

"Step One" is that a wide range of viruses are
present at low levels in "apparently healthy" colonies.

http://aem.asm.org/cgi/reprint/70/12/7185.pdf



"Step Two" is that varroa suck on the hemolymph of the 
few bees that have viruses, and spread them to not only
any subsequent bees that they feed upon, but they also
spread it to other mites that feed upon those bees.
The mites are the unwitting carrier of viruses that
the bees already had, spreading multiple viruses to
many bees, which spread them to many varroa, and so on.

http://aem.asm.org/cgi/reprint/72/1/606.pdf




> They weaken the bee so any pathogen has a chance. 

This may well be a factor in practical terms, 
but a weakened bee is not a requirement for 
infection - the viruses can infect "healthy bees" 
with ease.

> Vector assumes the diseases is with the mite,
> such as mosquitoes are a vector of malaria.

Judy Chen proved that individual mites do carry 
individual viruses, and some mites carry multiple
viruses, all infecting bees they bite, which then 
themselves become vectors for infecting other mites.
She even uses the term "vector" in her papers.

This is why multiple mites per brood cell is 
such a big sign, as Judy found that there was a
direct relationship between number of mites per
cell, and the odds of that bee (and all the
mites in the cell) having one or more viruses at 
hatch-out. 

*******************************************************
* Search the BEE-L archives at:                       *
* http://listserv.albany.edu:8080/cgi-bin/wa?S1=bee-l *
*******************************************************