Robin mentioned Braula - well I haven't seen one of those for about twenty years.  They used to be common in colonies, but since we have been pouring all these miticides in the hives, I guess it has become extinct here. 
I think that the small cells have enabled the bees to develop (learn?) some sort of behaviour (chewing out for example - but there must be others as well) that enables them to keep the Varroa population at a sub-lethal level.  Maybe it's a combination of Varroa not being able to reproduce as successfully on small cells and  anti-varroa behaviour.  Clearly the colonies on large cell have a much harder time with Varroa and need at least one treatment annually with an effective miticide or they will just become over-whelmed and collapse - it seems like the rapid increase in Varroa just doesn't give them time to react with any sort of behaviour that effects the Varroa population.  Always keep in mind that Lusby said that small cells was only about one third of this approach to combating Varroa - the other two being breeding and proper nutrition.
Best regards
Roger White
Superbee Cyprus.

::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
-- Visit www.honeybeeworld.com/BEE-L for rules, FAQ and  other info ---
::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::