Here is another not well done experiment which is inconclusive concerning
cell size and varroa control.

I bought small cell foundation and had fine years with little or no varroa.
But when I moved boxes around and added a third brood box to all my hives
with standard foundation, I still had little or no varroa. So cell size may
work, but I have not proved it.

There have been studies on cell size and varroa and entirely different
conclusions have been arrived at. One said there was no difference and
another said it worked, but even it hedged a bit.

I believed it would work because of earlier emergence of the workers and
drones, but have been told often and loudly that cell size does not make a
difference in time of emergence. That should be the only contributing
factor in reducing varroa loads in the hive if cell size works.

Bill Truesdell
Bath, ME