Africanized Honey Bees (AHB) -- also called Africanized bees or killer bees -- are descendants of southern African bees imported in 1956 by Brazilian scientists attempting to breed a honey bee better adapted to the South American tropics. Bee suits will protect against these dangerous stings.
When some of these bees escaped quarantine in 1957, they began breeding with local Brazilian honey bees, quickly multiplying and extended their range throughout South and Central America at a rate greater than 200 miles per year. In the past decade, AHB began invading North America.
more at: http://www.desertusa.com/mag98/sep/stories/kbees.html