Killer Bees

My friend and colleague Eugene Volokh links to a Slate story claiming killer bees are moving into the US at a surprisingly slow rate. (They have been found in Southern California, however, which makes them of considerable interest for both Eugene and myself.) As E ugene slyly puts it, "African-European miscegenation seems to be saving the day -- or ruining it, depending on whether you're human or a bee." Slate claims:

Another popular explanation for the bees' slowing migration is competition from European honey bees. Africanized queens are free to mate with European drones, and perhaps this has resulted in a dilution of the Africanized gene pool.

Unfortunately, I recalled seeing a news story to the contrary a while back. A little Google searching turned up the following story from the Agricultural Research journal:

Many experts expected that the farther from a tropical climate AHBs spread, the more they would interbreed with EHBs. But it appears that interbreeding is a transient condition in the United States, according to ARS entomologist Gloria DeGrandi-Hoffman. She is research leader at the Carl Hayden Bee Research Center in Tucson, Arizona, and ARS national coordinator for AHB research.

"Early on, we thought the mixing would reach a steady state of hybridization, because we knew the two groups of bees can easily interbreed and produce young," DeGrandi- Hoffman says. "But while substantial hybridization does occur when AHBs first move into areas with strong resident EHB populations, over time European traits tend to be lost."

The article explains that there are a number of biological reasons AHBs tend to prevail, one of which has to do with their ability to prevent "miscegenation."

EHB queen bees mate disproportionately with African drones, resulting in rapid displacement of EHB genes in a colony. This happens because AHBs produce more drones per colony than EHBs, especially when queens are most likely to be mating, DeGrandi- Hoffman explains.

"We also found that even when you inseminate a queen with a 50-50 mix of African drone semen and EHB semen, the queens preferentially use the African semen first to produce the next generation of workers and drones, sometimes at a ratio as high as 90 to 10," she says. "We don't know why this happens, but it's probably one of the strongest factors in AHBs replacing EHBs."

AHB genes apparently don't completely displace those of EHBs in a population, but the data seem to suggest that "miscegenation" is not what's saving the day. As the researchers noted:

Finally, some African traits are genetically dominant, such as queen behavior, defensiveness, and some aspects of foraging behavior. This doesn't mean that EHB genes disappear, but rather that hybrid bees express more pure African traits.