Lovely to see everyone chipping in on 4.9mm .....

Aaron asked:
> My question is, if indeed a smaller cell size makes for varroa tolerance
> what is it about a smaller cell size that impacts the varroa populations?
> Is it because there simply isn't enough room for the mites to be
successful?
> Is it something else (varroa moves to the suburbs where there's wide
open spaces)?  What is it?

Oh, I do like speculating!  How's this for starters:

i) as Aaron suggested, not enough room.  The mites can't move around so
freely in the cell so the male can't locate and mate with the females.
Sterile females result.
ii) maybe the cramped space makes it harder for mites to get to feeding
sites.
iii) maybe they can't get out of the way and get trapped more readily behind
the cocoon.
iv) small cell size somehow awakens hygienic behaviour of some kind, perhaps
more efficient uncapping of infested cells.  Didn't you observe something
like this Barry?
v) doesn't small cell size slightly accelerate the duration of the
larval/pupal stages?  If so, those last hours prior to emergence might make
a difference in nos of mature, mated female mites emerging.
vi) changes in temperature of the brood nest, pheromone levels, and other
sorts of arthropod lifestyle indicators that we may never understand.
vii) all of these working together?
viii) none of the above!

But, having speculated that real, tangible mechanisms for the possible
effect on Varroa of 4.9 are possible, I have to agree the mechanism doesn't
really matter.  It does though help give people some assurance that it might
be worth spending time trying it out.  Good luck to all who are
experimenting with it.

Gavin.