Within the past 40 years, Africanized honey bees spread from Brazil and now occupy most areas habitable by the species Apis mellifera, from Argentina to the southwestern United States. The primary genetic source for Africanized honey bees is believed to be the sub-Saharan honey bee subspecies A. m. scutellata. Mitochondrial markers common in A. m. scutellata have been used to classify Africanized honey bees in population genetic and physiological studies. Assessment of composite mitochondrial haplotypes from Africanized honey bees, using 4 base recognizing restriction enzymes and COI-COII intergenic spacer length polymorphism, provided evidence for a more diverse mitochondrial heritage. Over 25% of the "African" mtDNA found in Africanized populations in Argentina are derived from non-A. m. scutellata sources.