I seriously doubt you have africanized bees. See the link below for their farthest known spread. That being said, it does not mean that your bees are not bad tempered. Are you sure they superseded? How have you confirmed this? A great number if things can make your bees stingy. How old is the colony? Do you have a queen at all? Is their a predator coming at night and messing with the bees? Are the bees too hot? It may very well be that the queen was superseded and that a change in genetics has resulted in a change of demeanor. However, you should eliminate other possibilities. At any rate, the quickest way to change bee behavior is to get a new queen.
http://livingwithinsects.files.wordpres ... beemap.png