Have killer bees been around for long?

Africanized honey bees -- called 'killer bees' by Hollywood and the more sensationalist media -- are the result of some Tanzanian honey bee queens which escaped from a research establishment in Brazil in 1957 and mated with local drones. They formed feral (wild) colonies which have slowly spread southwards to the limits of tropical South America and northwards to the southernmost states of the US. They are unlikely to spread too much further because they don't tolerate cold winters.