What’s Buzzing with
What’s Buzzing with
Africanized Honey Bees?
In 1990, a honey bee swarm unlike any EHBs and create a hybridized, or Afri- Many experts expected that the farther
before found in the United States was canized, honey bee. from a tropical climate AHBs spread, the
identified just outside the small south This has always been a major ques- more they would interbreed with EHBs.
Texas town of Hidalgo. With that identi- tion for researchers—what, if any, type But it appears that interbreeding is a
fication, Africanized honey bees were no of interbreeding would happen between transient condition in the United States,
longer a problem we would have some AHBs and EHBs and how would this according to ARS entomologist Gloria
day. Africanized honey bees had arrived. affect honey bee traits that are important DeGrandi-Hoffman. She is research
Beekeepers, farmers who depend on to people, such as swarming and leader at the Carl Hayden Bee Research
honey bee pollination for their crops, absconding, manageability for bee- Center in Tucson, Arizona, and ARS
land managers, emergency responders keepers, honey production, and temper. national coordinator for AHB research.
like fire and police, and the public all “Early on, we thought the mixing
wanted to know what they would be fac- would reach a steady state of hybridiza-
ing as Africanized honey bees began to SCOTT BAUER (K11074-1)
tion, because we knew the two groups
spread. of bees can easily interbreed and produce
Now, 14 years later, scientists with the young,” DeGrandi-Hoffman says. “But
Agricultural Research Service and else- while substantial hybridization does oc-
where have uncovered many answers, cur when AHBs first move into areas
but they have also come upon some new with strong resident EHB populations,
and unexpected questions. over time European traits tend to be lost.”
Africanized honey bees—melodra-
matically labeled “killer bees” by A Mighty Adversary
Hollywood hype—are the result of honey DeGrandi-Hoffman and Stan Schnei-
bees brought from Africa to Brazil in the der, a professor of biology at the Uni-
1950s in hopes of breeding a bee better versity of North Carolina at Charlotte,
adapted to the South American tropical have been collaborating the past 3 years
climate. These honey bees reached the to figure out why AHBs replace EHBs
Brazilian wild in 1957 and then spread rather than commingling.
south and north until they officially “We’ve found six biological and be-
reached the United States on October 19, havioral factors we think are responsi-
1990. ble for making AHBs such successful
Actually, all honey bees are imports invaders,” Schneider explains.
to the New World. Those that flourished First, AHB colonies have faster
here before the arrival of Africanized growth rates, which means more swarms
honey bees (AHBs) are considered splitting off from a nest and eventually
European honey bees (EHBs), because dominating the environment.
Entomologist David Gilley is part of the
they were introduced by European team investigating the usurpation of Second is that hybrid worker bees
colonists in the 1600s and 1700s. EHBs European honey bee colonies by swarms of have higher amounts of “fluctuating
that escaped from domestication are Africanized honey bees. Because queenless asymmetry”—small, random differenc-
colonies are particularly susceptible to es between the left and right wings—than
considered feral rather than wild. usurpation, the team maintains a group of
Africanized honey bees are so called queenless colonies to lure usurpation African honey bees have, even when
because it was assumed that the African swarms into their apiary to be studied. raised in the same hive.
honey bees spreading out from Brazil Gilley is shown here requeening one of these “Imperfections like fluctuating asym-
“bait colonies.” metry that increase with hybridization
would interbreed with existing feral
4 Agricultural Research/March 2004
First found in southern
WHERE ARE Texas in 1990,
Africanized honey bees
THEY NOW ? are now found in most
of the Southwest.
may end up reducing worker viability destroy rival queens that are still devel- Finally, some African traits are genet-
and colony survival,” says DeGrandi- oping. African virgin queens are more ically dominant, such as queen behavior,
Hoffman. “But this is a controversial successful fighters, too, which gives defensiveness, and some aspects of
factor right now, and it will take long- them a significant advantage if they en- foraging behavior. This doesn’t mean that
term studies of African, hybrid, and counter other virgin queens in the colony. EHB genes disappear, but rather that
European colonies in the same habitat to DeGrandi-Hoffman and Schneider also hybrid bees express more pure African
truly understand its influence.” found that workers perform more bouts traits. The persistence of some EHB
But the third factor is undeniably true: of vibration-generating body movements genes is why the invading bees are still
EHB queen bees mate disproportionately on African queens before they emerge considered Africanized rather than
with African drones, resulting in rapid and during fighting, which may give the African, regardless of trait expression,
displacement of EHB genes in a colony. queens some sort of survival advantage. she points out.
This happens because AHBs produce AHB swarms also practice “nest usur- A coincidence may have contributed
more drones per colony than EHBs, espe- pation,” meaning they invade EHB col- greatly to an overwhelming takeover by
cially when queens are most likely to be onies and replace resident queens with AHBs in areas they’ve invaded. Just as
mating, DeGrandi-Hoffman explains. the swarm’s African queen. Nest AHBs began their spread throughout the
“We also found that even when you usurpation causes loss of European SCOTT B Southwest, the U.S.
inseminate a queen with a 50-50 mix of matrilines as well as patrilines. “In 11071-1)
African drone semen and EHB semen, Arizona, we’ve seen usurpation
the queens preferentially use the African rates as high as 20 to 30 percent,”
semen first to produce the next genera- says DeGrandi-Hoffman.
tion 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 An Africanized honey bee
(left) and a European
in AHBs replacing EHBs.” honey bee on
When an Africanized colony replaces honeycomb. Despite
its queen, she can have either African or color differences
European paternity. Virgin queens between these two bees,
normally they can’t be
fathered by African drones emerge as identified by eye.
much as a day earlier than European-
patriline queens. This enables them to
Agricultural Research/March 2004 5
feral honey bee population was heavily takeover by AHBs. Bill had a great deal ever documented. It’s even interested
damaged by another alien invader—the of foresight to take these samples,” ex- some as a model of how modern humans
deadly Varroa mite, an Asian honey bee plains geneticist J. Spencer Johnston, may have interacted with the European
parasite first found here in 1987. who is with the university. population of Neanderthals.
“Varroa mites emptied the ecological The data showed that within 3 years “Alan Templeton, a professor of biol-
niche of feral honey bees just as AHBs of the arrival of AHBs in the refuge there ogy and genetics at Washington Univer-
arrived,” says DeGrandi-Hoffman. “If was a turnover from predominantly EHB sity in St. Louis, has been looking at
they hadn’t been moving into a decimat- to predominantly AHB. From 1997 AHB spread as a demonstration of his
ed environment, AHBs might not have through 2001, the mixture stabilized, model of Homo sapiens’ evolution and
replaced EHBs so quickly.” with an average of 69 percent of the col- spread, which holds that there have been
onies made up of African queens mated three major migrations out of Africa,
Keeping Tabs on the Invaders with EHB and AHB drones and 31 per- with large amounts of genetic inter-
An extensive record of the AHB in- cent composed of EHB queens mated change among groups,” Johnston says.
vasion was created by now-retired ARS with AHB and EHB drones. This pro- Honey bee generations are short enough
entomologist William L. Rubink, who duced a genetic mixture rather than a that you can actually follow the invasion
was in the ARS Bee Research Unit in replacement of EHBs by AHBs. Addi- and the gene flow, unlike humans, ex-
Weslaco, Texas. From 1990 to 2001, tional sampling and more analysis of plains Johnston.
Rubink continuously sampled honey bee existing samples will be needed to see
colonies in the Welder Wildlife Refuge, whether this mixing continues or whether Where Did They Go?
about 30 miles north of Corpus Christi, the Africanized proportion increases, as Just how far and how fast AHBs have
Texas. has been predicted. spread in the United States may be one
Once Rubink retired, researchers from of the most surprising factors in the
Texas A&M University agreed to pre- Human Parallels? whole issue.
serve and analyze his samples. “We have In many ways, the spread of AHBs in Some experts predicted the bees
about 25 square feet of frozen bees that the Southwest has been one of the most would spread throughout the country;
represent the only real unbroken sam- successful in- SCOTT BAUER (K11073-2) others thought they’d reach only as far
pling of a wild area before and during its trogressions north as the latitude of Houston. Most
expected there would be a southern zone
SCOTT BAUER (K11073-1)
where AHBs would predominate, a
northern zone where EHBs would
maintain a climatic advantage, and a
large transitional zone between the two.
And everyone expected AHBs to spread
across the southernmost tier of states.
But, as of January 2004, AHBs have been
found only in southern California,
Arizona, New Mexico, Nevada, and
Texas, as well as Puerto Rico and the
U.S. Virgin Islands.
Why AHBs haven’t progressed east-
ward into Louisiana—though they were
expected there years ago—is a mystery.
So ARS entomologist José D. Villa be-
gan looking at factors that might corre-
late with where AHBs have spread. It
isn’t just minimum winter temperature
that limits AHB spread, as many be-
lieved, says Villa, who is in the ARS
Honey Bee Breeding, Genetics, and
Technician Mona Chambers measures the dimensions of an Africanized honey bee wing,
one of the traits that differentiate these bees from European bees. Inset: Closeup of the Physiology Research Unit in Baton
wings Chambers is viewing. Rouge, Louisiana.
6 Agricultural Research/March 2004
“What immediately jumped out at me has for beekeepers to manage their hives This defensiveness is probably the bees’
was the correlation with rainfall,” he in AHB areas. best-known trait. All honey bee behavior
says. “Rainfall over 55 inches, distribut- But requeening is a lot of work for runs the gamut from very defensive to
ed evenly throughout the year, is almost commercial beekeepers who maintain very docile and can change depending
a complete barrier to AHB spread.” thousands of hives. DeGrandi-Hoffman on temperature, humidity, cloud cover,
Total annual rainfall alone isn’t a bar- and Schnieder are currently trying to and food supply. But when provoked,
rier; AHBs have been found in areas of discover what triggers AHBs to usurp a AHBs do tend to sting in greater numbers
the Tropics with higher rainfall. But in hive. They suspect it could be a than EHBs.
areas with high rainfall distributed pheromone. “But they’re not anywhere near the
throughout the year, Villa’s pattern of “If we can find out what tells an AHB type of threat that Hollywood has made
AHB spread fits perfectly. swarm that this EHB nest can be taken them out to be,” DeGrandi-Hoffman
Villa is quick to point out that this is over or that a colony or queen is strong points out.
simply a mathematical correlation and and cannot be easily usurped, then we
not proof of cause and effect. But, he should be able to develop a chemical ‘no- Living with AHBs
says, “you do find that 55-inches-of- vacancy’ sign to help beekeepers keep While beekeepers obviously do not
rainfall point right at the edge of where AHBs out,” DeGrandi-Hoffman says. want to work with “hot bees,” people in
AHBs stopped moving east about 10 While AHBs do make honey and the Southwest have simply learned to live
years ago.” He’s planning experiments pollinate plants, two traits make them with AHBs. While many will never come
that may uncover the behavioral or physi- undesirable for beekeepers: Colonies in contact with the bees, others have had
ological mechanism that explains why. regularly abscond from hives, and they to learn new precautions.
How much farther AHBs may spread are often too defensive to be easily Retired ARS entomologist Eric
is still unknown. But if you apply the 55- tended. Erickson, who was with the ARS bee
inches-of-rainfall limit, there are still Because of AHBs’ genetic dominance center in Tucson, pioneered many safety
niches that the bees may fill, mainly in there has been little dilution of their methods in areas where people and
southern California. Southern Florida strong defensive reaction to threats to AHBs collide. He developed the first
would be hospitable to the bees given its their nests, explains DeGrandi-Hoffman. instructions for fire departments—often
temperature and rainfall, but regulatory
vigilance could keep them out, since the
area isn’t contiguous with the other ar- JACK DYKINGA (K7937-10)
eas of AHB spread. Alabama, northern
Florida, Louisiana, and Mississippi are
unlikely to be troubled by AHBs if the
55-inches-of-rainfall barrier holds.
Keeping on Beekeeping
One of the greatest challenges for
Southwest beekeepers has been main-
taining their EHB hives when they are
surrounded by AHBs.
Once AHBs spread to an area, bee-
keepers can no longer allow nature to
take its course in honey bee reproduction.
ARS has always recommended that
beekeepers regularly requeen their hives
with queens of known lineage to keep
AHB traits out of their apiaries. But,
given the African bees’ strong ability to
genetically usurp hives, the recom-
Northwest Fire District’s Captain John Estes of Tucson, Arizona, uses a wide spray of water
mendation is now to requeen with queens and chemical wetting agent as a means of subduing Africanized honey bees. Looking on is
that have already mated with EHB ARS entomologist Eric Erickson (retired), who taught this control method to fire
drones. It’s the best way ARS currently departments throughout Arizona.
Agricultural Research/March 2004 7
SCOTT BAUER (K11076-1)
the emergency responders in stinging
incidents. Most firetrucks already carried
a surfactant, a soapy liquid that helps put
fires out. Such soaps also kill honey bees
when sprayed directly on them. Erickson
also worked out ways to quickly convert
a firefighter’s basic turnout gear into a
protective bee suit. Fire departments all
over the Southwest are now trained in
Erickson also developed instructions
for homeowners to help them deal with
AHBs, such as how to prevent honey
bees from taking up residence inside
house walls and how to kill unwanted
bee colonies. (It is safer, though, to call
an experienced exterminator if at all
Swarm traps invented by entomolo-
gist Justin O. Schmidt, also at the Tucson Entomologist Justin Schmidt examines an ARS honey bee trap used to lure Africanized bee
bee center, have been a boon. swarms and prevent their establishment in walls of buildings. Captured swarms are easily
removed or destroyed with soapy water.
“We developed a simple, inexpensive
trap with a pheromone lure to attract
swarms looking for new nest sites. That’s
how we’re able to track honey bee colo-
SCOTT BAUER (K11075-1)
nies as they spread out,” Schmidt says. Varroa mites. But that rate varies
The traps are also used as prophylactic dramatically.
barriers around golf courses, airports, “I’ve looked at about 40 colonies.
schools, and botanic gardens, or any- Some have very few mites, and others
where else AHBs might take up resi- are loaded,” Eischen says. “But if these
dence and conflict with people. The traps had been EHB colonies without treat-
lure swarms away from high-traffic areas ment, they all would have died long ago.”
and make them easy to remove. He is trying to isolate which mechan-
ism provides the protection from Varroa
Not All Bad mites. He has already ruled out hygienic
People usually think only of AHBs’ behavior—the time it takes worker bees
downside, but they also represent a po- to clean out mites. But if he determines
tential positive. ARS entomologist Frank what AHBs do differently, it might be
A. Eischen at the Honey Bee Research possible to breed that desirable trait into
Unit in Weslaco, Texas, has been study- EHBs.—By J. Kim Kaplan, ARS.
ing AHBs for their resistance to Varroa This research is part of Crop Produc-
mites. tion, an ARS National Program (#305)
Eischen maintains an apiary in a re- described on the World Wide Web at
mote part of southern Texas. “Maintains” www.nps.ars.usda.gov.
may not be the right term, because he To reach scientists mentioned in this
simply leaves hive boxes out and lets the story, contact Kim Kaplan, USDA-ARS Judith Hooper assists David Gilley with a
bees fend for themselves year after year. Information Staff, 5601 Sunnyside Ave., gas chromatography/mass spectroscopy
All the honey bees in the apiary have Beltsville, MD 20705-5128; phone (301) procedure for analyzing volatile
long since been Africanized. 504-1637, fax (301) 504-1648, e-mail pheromones from Africanized honey bees.
Pheromones appear to be an important
His AHBs, which are never treated, email@example.com. ★ component of successful nest usurpation.
have a slightly better survival rate against
8 Agricultural Research/March 2004