The Africanized honey bee found in the western hemisphere descended from 26 Tanzanian queen bees accidentally released by a replacement bee-keeper in 1957 near Rio Claro, São Paulo State in the southeast of Brazil. Biologist Warwick E. Kerr had interbred honey bees from Europe and southern Africa.
Hives containing these particular queens were noted to be especially defensive. Kerr was attempting to breed a strain of bees that would be better adapted to tropical conditions (i.e., more productive) than the European bees used in North America and southern South America.
The hives from which the bees were released had special excluder grates which were in place to prevent the larger queen bees from getting out but to allow the drones free access to mate with the queen. Unfortunately, following the accidental release, the African queens eventually mated with local drones, and their descendants have since spread throughout the Americas.
The Africanized hybrid bees have become the preferred type of bee for beekeeping in Central America and in tropical areas of South America because of improved productivity. However, in most areas the Africanized hybrid is initially feared because it tends to retain certain behavioral traits from its African ancestors that make it less desirable for domestic beekeeping.
Specifically (as compared with the European bee types), the Africanized bee: