Exactly why this has occurred is unknown. We discuss the possible influence of some of these factors below. However, this seems an inadequate explanation of why the bees have not spread further into the eastern and northern parts of Texas, which have no apparent geographic barriers. In California, AHB has been restricted to the southeastern portion of the state and hasn't made very strong incursions despite having a fairly wet winter in 1995 with profuse spring blooms in the desert to aid its migration. The US is not the first region where AHB have encountered large populations of European honey bees.
Africanized bees build in exposed locations more frequently than do European bees.
Previous predictions Several predictions of the final expansion of AHB in the United States have been made based upon various assumptions of low temperature limits. The most conservative of these has AHB inhabiting just the southern extremes of the United States, approximately the area it currently is occupying, but also including all of Florida and the southern Gulf states. However, some studies have shown that AHB can tolerate cold temperatures for sustained periods of time, and these studies have led others to extrapolate that AHB might extend as far as the mid-United States or even survive in climates all the way into Canada, Michigan and Maine. However, these effects will not be known until AHB reaches the northern limits of its expansion. An uncertain future The rate of expansion of AHB in the Western Hemisphere has slowed from its torrid 300 miles per year pace through the tropics to an almost stagnant rate in the United States.