Why are African bees able to tolerate mites where European bees are not?

* Short post capping period fails to limit varroa buildup

> The extremely high numbers of varroa mites found in Cape honeybees (>30 000 in some colonies) indicates however, that although the short post-capping period of Cape bees must limit mite population growth to some extent, it is insufficient to prevent mite levels increasing to harmful levels. This data also indicates that the general presence of drone brood for much of the year is crucial to mite population growth. (Allsopp)

* African bees have a much shorter lifespan

> The short adult longevity of AHB (21 days versus 25–180 days for EHB) as a result of the tropical or sub-tropical climate indicates that >12 000 mites are needed to kill an AHB colony. Therefore, although DWV is present in AHB and A. cerana colonies, mite populations stabilize at levels well below that required to kill the colony.

> The constant production of worker brood and reduced adult longevity of AHB under tropical conditions reduce the transmission of the virus between adult bees and brood. Therefore the size of the mite population needed to kill an AHB colony will be greater than that required to kill an EHB colony.

> It is still important that the tolerance mechanism which is operating in AHB be fully understood, since this is the only race of A. mellifera known to be tolerant to Varroa which has had such a devastating affect on all other races of A. mellifera.

-- 
Africanized honeybees have unique tolerance to Varroa mites
Stephen J. Martin and Luis M. Medina
TRENDS in Parasitology Vol.20 No.3 March 2004

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