Ibrahim & Spivak 2006 also reported:

Our findings indicated that bees bred for SMR express hygienic behavior; adult bees selectively remove pupae infested with mites. In addition, there is an effect of SMR pupae that reduces mite reproductive success that requires further investigation. Within the incubator, the reproductive success of mites was lower on SMR worker pupae.

The mechanism for this effect of brood type on mite reproduction is unknown and remains to be investigated. It is possible that the same factor that hinders mite reproduction also affects the development and viability of the pupa itself, as some colonies bred for SMR have very low brood viability.

comment:
I remember when these lines were first developed there was talk that while SMR traits caused mites to reproduce poorly, it also caused the bees to reproduce poorly, sometimes preventing the colonies from ever building up properly. Then they crossed them with regular stock to restore viability which in turn, greatly reduced the mite suppression. 

PLB

thinking: dog bites own tail

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