I'm not sure whether the authors have realised this but lack of difference in amount of uncapping doesn't mean there isn't a difference in uncapping (!). Whilst I am loathe to facilitate unevidenced musings, there is a potential mechanism (FAO
@Beesnaturally).
It is
possible (but
not observed) that the treated vs untreated may have similar levels of uncapping but the nature of the uncapping varies between the two groups. For example if treated colonies uncap anything but the untreated only uncap cells with higher numvers of mites, this would select for less fecund mites. It is possible that the overall uncapping per colony is similar, just better discrimination with untreated.
As stated, this is NOT something which has been documented but it gives a conceivable mechanism.
This does not mean it is occurring and the comments about study size are still as valid.