Peter wrote

> Many reports have come out of South and Central America that varroa is not
a significant problem with the Africanized bees there. Several theories have
been promoted.

The theory that I heard was that the Varroa destructor was the Japanese
haplotype which is less virulent than the Korean haplotype.  This having
been directly introduced from Japan via Apis mellifera hives taken to South
America.  When the Africanised bee hit the USA, it came in contact with the
Korean haplotype and thus its progress was slowed.

FWIW

Trevor Weatherhead
AUSTRALIA