The study, published in this week’s edition of the journal PLOS ONE, found that more than 60 percent of the foraging honey bees in San Diego County are Africanized and that Africanized bees can now be found as far north as California’s delta region.

“Our study shows that the large majority of bees one encounters in San Diego County are Africanized and that most of the bees you encounter are from feral colonies, not managed hives,” said Joshua Kohn, a professor of biology at UC San Diego who headed the study.

“The pattern of Africanization we documented in San Diego County and elsewhere in California appears consistent with patterns previously documented in Texas, where Africanized honey bees first appeared in the United States. After the initial wave of hybridization, the remaining bees have a mixture of African and European genes, with the majority of the genome from Africa.”

Africanized bees are hybrids of a subspecies from southern Africa that were brought to Brazil to improve honey production, but escaped and spread throughout South America and Central America, arriving in Mexico in 1985 and Texas in 1990. Their aggressive behavior and tendency to swarm victims have led them to be dubbed “killer bees.” Read more.