Re: Drone cell size.
Normal cell size for worker cells is 5.25mm. The cell size is an average of what worker cells measured when the comb was removed from box hives that were being changed out for modern frame hives. These measurements were made before 1893, the year that Ursmar Baudoux put forth his idea of larger bees being more efficient. Worker cells were measured by Langstroth, Dadant, Root, Doolittle, Dr. Gallup, Dr. C. C. Miller and many others. They said normal worker cell size was in a range of 5.1 to 5.2. When A.I. Root made his first foundation mill he made the cell size 5.0mm and the bees used it, but the queens were reluctant to lay in it if they could find slightly larger cells. When his son H. H. Root built a mill later, and used the 5.2mm size, the queens used those size cells with no hesitation. To my mind honey bee queens are the authority on cell size, and they prefer the range of 5.1 on the low side to 5.4mm on the high side. I think the larger 5.4 cell size is because the manufactures wanted an all purpose size, one the bees would use for brood and a cell size large enough to make honey extraction easy.
Drone cell size was not increased to my knowledge, the researcher was on the worker. Drone cells are around 6.4mm to 6.8mm in size.
Varroa does not reproduce as fast in worker brood, but it is not because of the cell size.
Infestation by varroa mites damages drones in many ways, exposure to chemicals will damage them also. To produce drones for mating we need to control varroa and do it in a manner that is least damaging to queens and drones. We should also increase the numbers of drone producing colonies around our mating yards and not rely on "wild colony drones" to mate with our virgins.
38 years - 25 colonies, 32 Nucs - IPM disciple - Naturally Skeptic