20 years ago, in 1989, Deborah Roan Smith and Orley Taylor described  
the situation where in 30 short years, most of South and Central  
America had been "invaded" by African honey bees. They state quite  
plainly that it is "unclear" whether the bees are a hybrid of European  
and Africans, or represent an essentially pure African population.  
Using the relatively new technique of mapping mitochondrial DNA, it  
was found that bees of Brazil, Venezuela and Mexico were 97% African  
(scutellata) type. Their analysis seems to indicate that the gene flow  
is one directional, probably due to fact that the propagation is  
mainly via queens, and not drones. They state that there is no  
evidence that the feral population is significantly "Europeanized".  
One could logically assume that Africanization would continued  
unchecked into the US until it reached a climate barrier, as it has in  
South America.

Some years later, in 2000, this scenario had come about. Ernesto  
Guzman wrote about it and points out that hybridization may still  
prevail at the northern limit.

 > THE SUB-SAHARAN RACE of the honey bee (A. m. scutellata) has made  
an unprecedented sweep across South and Central America and is  
currently spreading into North America. There is increasing evidence  
that the previous gene pool, derived from a mixture of European races,  
has largely been replaced by the A. m. scutellata genotype in these  
areas. This has occurred despite the fact that the honey bee races  
interbreed freely.

 > At the leading edge of Africanization in California, >95% of the  
colonies identified as Africanized by morphometrics had A. m.  
scutellata mitochondrial  genotypes suggesting that selection or  
reproductive isolation is maintaining the correlation between  
mitochondrial and nuclear genomes. Thus, mitochondrial genotype alone  
may be a strong indicator of both maternal and paternal inheritance,  
in most geographical areas. However, at the extreme southern limits of  
the range of A. m. scutellata in South America, there appears to be  
considerable genetic mixing between A. m. scutellata and the  
previously existing European feral bees. This situation is expected to  
occur at the eventual northern limit of Africanized bee spread as well.

 > In North America, hybridization between these races is expected to  
be considerable at the northern extreme of the geographical range of  
Africanized bees. In this situation, mitochondrial analysis will  
provide a discrete genetic marker of Africanization that will  
compliment diagnostic genomic DNA markers.

Meanwhile, the bees of the Yucatan were studied:

 > Since the arrival of Africanized bees, the genetic architecture of  
the Yucatecan population of honeybees has changed dramatically. By  
1998 (13 years after the arrival of Africanized bees) there had been a  
dramatic increase in the proportion of African nuclear alleles  
estimated in the managed Yucatecan population (65%) and, similarly,  
the gene pool of the feral population contained an estimated 63%  
African nuclear alleles.  Africanized bees have a competitive  
advantage over European bees in the Neotropics, in terms of their  
colonizing abilities and rules of reproduction and dispersal.

Finally, in 2004, we have the following summary, written by  
researchers living and working with African bees in Arizona.

 > One of the more remarkable aspects of the African bee is its  
ability to displace European honey bee subspecies in the New World.  
Initially, it was assumed that African and European bees would  
interbreed, giving rise to the “Africanized honey bee” of Latin  
America. However, although substantial hybridization occurs when  
African bees invade areas with European populations over time European  
characteristics tend to be lost. Indeed, throughout much of its range  
in the New World, the invading honey bee population has remained  
essentially African in its nesting biology, swarming and absconding  
behavior, foraging and diet selection, and mitochondrial DNA.

 > While some introgression of European alleles has occurred, African  
genetic and *behavioral* characteristics have been largely preserved  
during the invasion process. For brevity, we refer to the descendants  
of A. m. scutellata in the Americas as *African bees*

ref available on request

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