In your study VSH factor counting was done by dividing the number of cells opened by bees with the number of cells examined. This was done by comparing fotographs taken at 10 days versus 20 days brood age. The porpotion of opened cells together with infestation rate ( of donor colony?) was used to determine VSH factor.

This is not the usually used method to determine VSH factor. This does n...

Why is brood volatiles induced by varroa mites not considered as explaining factor? You conclude that "brood volatiles are not a factor in the results obtained." These mite induced volatiles have been similar in both groups, but they may still be the key factor behind differencies. Discussion goes on in Beesource forum.