African Honey Bee Update
The more they are studied, the more we know, but more questions
keep finding their way to the top... Article writen by Kim Kaplan,
USDA-ARS Information Staff. published in the March issue of Agricultural
Research.
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-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."
A Mighty Adversary
DeGrandi-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
DeGrandi-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, 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."
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. DeGrandi-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 usurpation 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."
Since this is a somewhat long article - click
here to finish it .......
Keeping Tabs on the Invaders
Where Did They Go?
Keeping on Beekeeping
Living with AHBs
Not All Bad