The resistance/tolerance (two different phenomena) of 
African/Africanized bees is not as clear cut as many think.  And even 
murkier is the question of what mechanism(s) may have the greatest 
effect in curbing varroa mites.  The advancing front of Africanized 
bees through northern South America, Central America, and even into the 
USA did not carry or encounter varroa until after the bees had been 
in each country for some time.  So what emerged in Brazil as 
resistance/tolerance may have occurred there and not in other 
countries.  The real (or perceived) need to treat confirms this view: 
Brazilian beekeepers in general do not treat, in other countries they 
claim to have to treat or varroa will take over.  Puerto Rico seems to 
have developed a unique subtype of Africanized bees- gentler, and not 
requiring treatment.

As for mechanisms, the literature from Brazil documents a number of 
mechanisms (infertility of mites in brood, grooming, 
uncapping/recapping, generalized hygienic behavior), as isolated 
reports, but as best as I know no one has looked at them in concert to 
extract the relative contribution of each one.  E. Guzman-Novoa did 
that in Mexico and found no single strong mechanism.  In terms of the 
effect of uncapping/recapping in reducing mite growth in colonies, the 
effect on reproduction is relatively small, at least relative to the 
effect of highly specific removal of infested worker brood cells at the 
level of colonies with VSH (varroa sensitive hygiene).  

 

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