Climate Change and Killer Bees: Northward Expansion in California

The Africanized honey bee is a hybrid of the European and African honey bees. It was introduced to California in 1994, and has been rapidly expanding ever since. This "killer bee"--so-called because they attack intruders in numbers much greater than the European honey bees do--was recently seen as far north as California's Delta Region, according to University of California-San Diego researchers.

"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," Joshua Kohn, study leader and a professor of biology at UC San Diego, said in a news release.

According to their study, the researchers found that more than 60 percent of honey bees in San Diego are Africanized.

"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," Kohn added in the release.

In order to determine how far and how fast these bees are spreading, the researchers examined genetic markers of 265 honey bees that were collected from 91 sites throughout California. While Africanized bees are able to expand their range upwards of 500 kilometers annually, the UC San Diego researchers found that in California the bees had only traveled 250 kilometers from their northernmost location reported in 2006. This suggests that the killer bee expansion has declined in California, according to the researchers.

The researchers further explained that this could be a result of the bees reaching their northern expansion limit, because they are sensitive to cold temperatures. However, based on predictions of future climate change models, the killer bees' territory is subject to change again, as the release noted.

"Feral Africanized bees have replaced European ones everywhere from Brazil to California," Kohn said in a statement. "Part of the reason for this is their increased aggression, but there may be other factors. For instance, Africanized honey bees may be better able to resist certain diseases that afflict honey bee colonies. By dissecting the genomes of Africanized honey bees to find regions responsible for advantageous traits, we may be able to combat recent declines in managed honey bee populations that are so critical for food production."

Their findings were recently published in the journal PLOS ONE.

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