The recent confirmation of Africanized honey bees in Modesto--the first confirmed case north of Madera County—is “probably an isolated case, and there probably aren’t any more Africanized honey bee colonies in the northern San Joaquin Valley,” Extension apiculturist Eric Mussen, based at the University of California, Davis Department of Entomology, said.

“I don’t think they moved there on their own,” Mussen said. “They probably swarmed during or just after the almond pollination season. The migratory beekeeper left but the bees didn’t.”

Unfortunately, the Africanized bees colonized in shrubbery along a well-traveled pedestrian and bicycle route and attacked a 70-year-old man and his three dogs on July 5 after one dog disturbed the nest. The man sustained as many as 60 bee stings, mostly on the face, as he ran an eighth of a mile to a residence.

A recently released laboratory report from the California Department of Food and Agriculture positively identified the bees as Africanized, known in the Hollywood movies as “killer bees.”

The Africanized bees may have come from Arizona, Texas, Florida or southern California, Mussen said.  Migratory beekeepers from all over the country truck in their bees to pollinate California’s 800,000 acres of almonds, located in the Central Valley from Butte to Kern counties. Each acre requires two bee colonies for pollination.

Africanized bees swarm more often their cousins, the European honey bee, the most common bee in the United States.

“The attack is troubling but I doubt there are any more Africanized honey bee colonies swarms in that valley,” Mussen reiterated. “Otherwise, more people would have encountered them in Fresno and Merced counties before they even reached Modesto in Stanislaus County.”

“There’s no way to tell if honey bees are Africanized without DNA testing,” Mussen said. “They look about the same as the European honey bee.  They tend to be a little darker than European honey bees and a little smaller. What sets them apart is their intensive defensive behavior. They’ve been known to chase their victims a quarter of a mile.”

When beekeepers find intensive defensive behavior in their hives, they kill the queen bee and “requeen” the colony. “Over four to six weeks, the original workers die of old age and the new queen replaces them with more daughters,” Mussen said.

Africanized honey bees are the result of attempts to hybridize European honey bees with an African race, Mussen said. Researchers brought Tanzanian queen bees (Apis mellifera scutella)  to Brazil in the 1950s.  In 1957, some of the African bee descendants escaped from the researchers and beekeepers and began expanding their territory.

The descendants reached southern Texas in 1990 and southern California in 1994. “In California, they were first found “just outside of Blythe, in Riverside County,” Mussen said.

California State Department of Food and Agriculture officials say the hybrid is now established in more than a dozen counties in the state, primarily those south of a diagonal line that runs northeast to southwest, from northern Tulare County to the southwest corner of San Luis Obispo County.

They include Imperial, Kern, Los Angeles, Madera, Orange, Riverside, San Bernardino, San Diego, Tulare and Ventura counties. Also affected are portions of Inyo, San Luis Obispo and Santa Barbara counties.

Madera is considered the most northern county to be colonized, but Mussen believes it likely isn't colonized. Only one case of Africanized honey bees has been confirmed since 2004.