It just happens that Warwick Kerr and Walter Rothenbuhler co-authored a paper together in 1968. From it, it is quite clear that nobody had a handle on aggressive behavior at that point, quite a few years after the introduction of African bees into Brazil. 

They wrote:

Stinging behavior of bees has been considered genetically in a preliminary
way. Two inbred lines differed widely in temperament. The
Brown line stung at the rate of about 1.5 stings per brief colony visit and
manipulation, whereas the Van Scoy line stung at the rate of about 0.01
times per identical visit. It was concluded
that more than two loci underlie the differences in stinging behavior.

The experience with African bees (Apis mellifera adansonii) in Brazil
makes the Brown line seem gentle. This bee was introduced into Brazil
in 1956 with the intention of using it in a careful breeding program.
It has a number of apiculturally desirable features, but unfortunately is
very cross. The differences in temperament between Italian and African
bees is under study by a method developed by Stort.

BEE GENETICS (1968)
WALTER C. ROTHENBUHLER, JOVAN M. KULINCEVIC
The Ohio State University, Columbus, Ohio, U.S.A.
WARWICK E. KERR
Universidade de sao Paulo, Ribeirao Pre to, Brazil

             ***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software.  For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html

Guidelines for posting to BEE-L can be found at:
http://honeybeeworld.com/bee-l/guidelines.htm