The Africanized bee, also known as the "Killer Bee" is a cross between the European honey bee and 26 queen bees brought over from what is now known as Tanzania in Africa to Brazil in 1957. The idea was to breed a bee that was a good honey producer and would be able to tolerate hot temperatures.
The African bee they chose to work with, although adapted to hot temperatures, was a bee that had evolved to defend the hive ferociously and had the tendency to swarm easily.
During a hive inspection the queen excluders were inadvertantly left off, queens escaped and began breeding with the local bees. This might not have been a bad thing except for the fact that the agressiveness and the swarming tendencies were dominant traits leading to the breed of bees we are now dealing with.
African bees are now in southern California, southern Nevada, Arizona, New Mexico, Texas and Florida. It is believed that they will not be able to migrate north because of the cold but with the winters getting warmer it is not known how far north they will spread.
The presence of Africanized traits will have already changed the dynamics of beekeeping in these areas.
I have known beekeepers from central and South America who actually keep African bees and would not go back to having an all European bee. Why? Because it seems that the problems that are plaguing our bees such as mites are not a problem with Africanized bees and these bees are better honey producers because they are so competitive. These beekeepers have been very vigilant in distroying the most agressive colonies and selectively breeding from the gentler ones.
A common misconception is that their sting is more potent but this is not true. The problem is that more bees will leave the hive and attack if disturbed and they will follow up to a quarter of a mile in pursuit of the offender.
Time will tell as to how far north they will migrate and beekeepers will have to adjust their beekeeping techniques. I have the feeling that many hobby beekeepers will choose to hang up their smokers rather than deal with this bees.