Africanized, or ‘killer’, bees form aggressive swarms and have largely replaced local populations across South and Central America. They emerged in Brazil in the 1960s, when introduced African honeybees bred with domestic European ones. To understand their success, a team led by Matthew Webster at Uppsala University in Sweden analysed the genomes of 32 Africanized honeybees (Apis mellifera).
The team found that most of the bees’ ancestry was African in origin, but that one long stretch of DNA was inherited from European ancestors — a sign that it was beneficial to the hybrids. Genes on this DNA segment have been linked to reproduction and foraging, and these traits might have propelled the wide spread of killer bees.