AFRICAN HONEY BEE UPDATE

 

In 1990, a honey bee swarm unlike any before found in the United States was identified just outside the small south Texas town of Hidalgo. With that identification, Africanized honey bees were no longer a problem we would have some day. Africanized honey bees had arrived.
Beekeepers, farmers who depend on honey bee pollination for their crops, land managers, emergency responders like fire and police, and the public all wanted to know what they
would be facing as Africanized honey bees began to spread.

Now, 14 years later, scientists with the Agricultural Research Service and elsewhere have uncovered many answers, but they have also come upon some new and unexpected questions.

.Africanized honey bees-melodramatically labeled "killer bees" by Hollywood hype-are the' result of honey bees brought from Africa to Brazil in the 1950s in hopes of breeding a bee better adapted to the South American tropical climate. These honey bees reached the Brazilian wild in 1957 and then spread south and north until they officially reached the United States on October 19, 1990.
Actually, all honey bees are imports to the New World. Those that flourished here before the arrival of Africanized honey bees (AHBs) are considered European honey bees (EHBs), because they were introduced by European colonists in the 1600s and 1700s. EHBs that escaped from domestication are considered feral rather than wild,

Africanized honey bees are so called because it was assumed that the African honey bees spreading out from Brazil would interbreed with existing feral EHBs and create a hybridized, or Africanized, honey bee.
This has always been a major question for researchers-what, if any, type of interbreeding would happen between AHBs and EHBs and how would this affect honey bee traits that are important to people, such as swarming and absconding, manageability for beekeepers, honey production, and temper.
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-Hoffglan. 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," DeGrandiHoffman 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."

DeGrand-Hoffman and Stan Schneider, a professor of biology at the University of North Carolina at Charlotte, have been collaborating the past 3 years to figure out why AHBs replace EHBs rather than commingling.

'We've found six biological and behavioral factors we think are responsible for making AHBs such successful invaders," Schneider explains. First, AHB colonies have faster growth rates, which means more swarms splitting off from a nest and eventually dominating the environment. Second is that hybrid worker bees have higher amounts of "fluctuating asymmetry"-small, random differences between the left and right wings-than African honey bees have, even when raised in the same hive.
"Imperfections like fluctuating asymmetry that increase with
hybridization may end up reducing, worker viability and colony survival," says DeGrand i-Hoffman. "But this is a controversial factor right now, and it will take long-term studies of African, hybrid, and European colonies in the same habitat to truly understand its influence."
But the third factor is undeniably true: 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, DeGrand i-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."
When an Africanized colony replaces its queen, she can have either African or European paternity. Virgin queens fathered by African drones emerge as much as a day earlier than European-patriline queens. This enables" them to destroy rival queens that are still developing. African virgin queens are more successful fighters, too, which gives them a significant advantage if they encounter other virgin queens in the colony. DeGrand i-Hoffman and Schneider also found that workers perform more bouts of vibration-generating body movements on African queens before they emerge and during fighting, which may give the queens some sort of survival advantage.

AHB swarms also practice "nest usurpation," meaning they invade EHB colonies and replace resident queens with the swarm's African queen. Nest usurpation causes loss of European matrilines as well as patrilines. "In Arizona, we've
_seen I u§urpation rates as high as 20 to 30 percent," says DeGrandi-Hoffman. . '
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. The persistence of some EHB genes is why the invading bees are still considered Africanized rather than African, regardless of trait expression, she points out.

A coincidence may have contributed greatly to an overwhelming takeover by AHBs in areas they've invaded. Just as AHBs began their spread throughout the Southwest, the U.S. feral honey bee population was heavily damaged by another alien invader-the deadly Varroa mite, an Asian honey bee parasite first found here in 1987. "Varroa mites emptied the ecological niche of feral honey bees just as AHBs arrived," says DeGrandi-Hoffman. "If they hadn't been moving into a decimated environment, AHBs might not have replaced EHBs so quickly."

SOURCE: USDA Agricultural Research/March 2004.