This is a thread that has run and run over and over again.

Cold does not seem to be that important a factor in this bee, but
something latitude linked, probably associated with day length or
seasonality, certainly does come into play. In an earlier run of this
discussion Garth Cambray pointed out that A.m.scutellata existed
perfectly well up into the higher mountains in South Africa where frost
and snow are not unusual.

No african/africanised bees exist in their long time ranges in Africa
and South America  much north or south of a latitude of 30 to 35 degrees
either side of the equator. They have had a very long time to spread in
Africa, yet despite the opportunity to do so they have never fully
travelled up through the continent to the land bridge to Europe, and at
the south end of their range the small area of the Cape bee remains, and
is generally stable.

They have not travelled very far south in Argentina either, and have
apparently come to a halt.

You possibly do not need to look any further than a natural, possibly
insignificant to us, factor being at work here which means they may be
at, or close to, their limiting latitudes in North America.


--
Murray McGregor