Answers to the Puzzling Distribution of Africanized Bees in the United States or "Why are those Bees not Moving East of Texas?"

Authors: Villa, Joseph; Rinderer, Thomas; Stelzer, John

Submitted to: American Bee Journal
Publication Type: Popular Publication
Publication Acceptance Date: 1/1/2002
Publication Date: 2/1/2002
Citation: Villa, J.D., Rinderer, T.E., Stelzer, J.A., 2002. Answers to the Puzzling Distribution of Africanized Bees in the United States or "Why are those Bees not Moving East to Texas?", American Bee Journal 142(7):480-483.

Interpretive Summary: Africanized honey bees occupied all of tropical Latin America in less than three decades. Their high defensive behavior and other colony characteristics stongly impacted beekeepers and the general public. Research on the temperature tolerance of these colonies had predicted that similar situations would eventually occur in the most southern areas of the southernmost states from California to Florida. Starting in 1990, Africanized colonies have been found in areas predicted to be favorable due to moderate winter temperature in the Southwest. Noticeable effects of these bees have been experienced in southern Texas and Arizona. Contrary to prior predictions, no natural movement of Africanized bees has occurred east of Texas. An analysis was conducted of possible factors explaining this anomalous distribution of Africanized bees. The analysis confirms the negative effects of low winter tmperature, and points to previously unknown negative effects from factors associated with higher rainfall along the Gulf Coast. It is highly unlikely that Africanized bees will expand their range along the Gulf Coast from Louisiana to Florida. They will definitely not have a noticeable permanent impact on beekeeping and the public in these areas.

Technical Abstract: Africanized honey bees (AHB) have occupied areas of the southwestern United States, but unexpectedly have not been discovered along the Gulf Coast east of Texas. The association between environmental factors (average minimum low temperature and average annual rainfall) and between Solenopsis invicta density (mounds per acre) and the current distribution of Africanized honey bees (AHB) was analyzed. The relationship between the average values for these three parameters in each county and whether a county was positive or negative for AHB finds was established. Counties in areas of Texas, New Mexico, Arizona and California were considered to have been potentially at risk if they had been closer than 100 miles from a positive find of AHB for at least one year. The proportion of positive AHB counties with respect to counties potentially at risk decreases dramatically with lower average minimum temperatures and the increasing rainfall, but there is no clear relationship with the density of red imported fire ants. Rainfall above 50 inches per year seems to explain the lack of movement east of Texas. Several hypotheses for how high rainfall might be influencing AHB bee colony growth and swarming cycles, or how higher humidity may affect the intensity of parasitism by Varroa destructor are discussed.