Did They Go?
Just how far and how fast AHBs have spread in
the United States may be one of the most surprising factors in the whole issue.
Some experts predicted the bees would spread throughout the
country; others thought they'd reach only as far north as the latitude of
Houston. Most expected there would be a southern zone 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 eastward into Louisianathough
they were expected there years agois a mystery. So ARS entomologist
José D. Villa began looking at factors that might correlate with where
AHBs have spread. It isn't just minimum winter temperature that limits AHB
spread, as many believed, says Villa, who is in the ARS Honey Bee Breeding,
Genetics, and Physiology Research Unit in Baton Rouge, Louisiana.
"What immediately jumped out at me was the correlation
with rainfall," he says. "Rainfall over 55 inches, distributed evenly
throughout the year, is almost a complete barrier to AHB spread."
Total annual rainfall alone isn't a barrier; AHBs have been
found in areas of the Tropics with higher rainfall. But in areas with high
rainfall distributed throughout the year, Villa's pattern of AHB spread fits
Villa is quick to point out that this is simply a mathematical
correlation and not proof of cause and effect. But, he says, "you do find
that 55-inches-of-rainfall point right at the edge of where AHBs stopped moving
east about 10 years ago." He's planning experiments that may uncover the
behavioral or physiological mechanism that explains why.
How much farther AHBs may spread is still unknown. But if you
apply the 55-inches-of-rainfall limit, there are still niches that the bees may
fill, mainly in southern California. Southern Florida would be hospitable to
the bees given its temperature and rainfall, but regulatory vigilance could
keep them out, since the area isn't contiguous with the other areas 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 maintaining their EHB hives when they are surrounded by AHBs.
Once AHBs spread to an area, beekeepers 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 recommendation is now to requeen with
queens that have already mated with EHB drones. It's the best way ARS currently
has for beekeepers to manage their hives in AHB areas.
But requeening is a lot of work for commercial beekeepers who
maintain thousands of hives. DeGrandi-Hoffman and Schnieder are currently
trying to discover what triggers AHBs to usurp a hive. They suspect it could be
"If we can find out what tells an AHB swarm that this EHB
nest can be taken over or that a colony or queen is strong and cannot be easily
usurped, then we should be able to develop a chemical 'no-vacancy' sign to help
beekeepers keep AHBs out," DeGrandi-Hoffman says.
While AHBs do make honey and pollinate plants, two traits make
them undesirable for beekeepers: Colonies regularly abscond from hives, and
they are often too defensive to be easily tended.
Because of AHBs' genetic dominance there has been little
dilution of their strong defensive reaction to threats to their nests, explains
DeGrandi-Hoffman. This defensiveness is probably the bees' best-known trait.
All honey bee behavior runs the gamut from very defensive to very docile and
can change depending on temperature, humidity, cloud cover, and food supply.
But when provoked, AHBs do tend to sting in greater numbers than EHBs.
"But they're not anywhere near the type of threat that
Hollywood has made them out to be," DeGrandi-Hoffman points out.
Living with AHBs
While beekeepers obviously do not want to work with "hot
bees," people in the Southwest have simply learned to live with AHBs.
While many will never come in contact with the bees, others have had to learn
Retired ARS entomologist Eric Erickson, who was with the ARS
bee center in Tucson, pioneered many safety methods in areas where people and
AHBs collide. He developed the first instructions for fire
departmentsoften 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's methods.
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 possible.)
Swarm traps invented by entomologist Justin O. Schmidt, also at
the Tucson bee center, have been a boon.
"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 colonies as they spread out," Schmidt says.
The traps are also used as prophylactic barriers around golf
courses, airports, schools, and botanic gardens, or anywhere else AHBs might
take up residence and conflict with people. The traps lure swarms away from
high-traffic areas and make them easy to remove.
Not All Bad
People usually think only of AHBs' downside, but they also
represent a potential positive. ARS entomologist Frank A. Eischen at the Honey
Bee Research Unit in Weslaco, Texas, has been studying AHBs for their
resistance to Varroa mites.
Eischen maintains an apiary in a remote part of southern Texas.
"Maintains" may not be the right term, because he simply leaves hive
boxes out and lets the bees fend for themselves year after year. All the honey
bees in the apiary have long since been Africanized.
His AHBs, which are never treated, have a slightly better
survival rate against Varroa mites. But that rate varies dramatically.
"I've looked at about 40 colonies. Some have very few
mites, and others are loaded," Eischen says. "But if these had been
EHB colonies without treatment, they all would have died long ago."
He is trying to isolate which mechanism provides the protection
from Varroa mites. He has already ruled out hygienic behaviorthe
time it takes worker bees to clean out mites. But if he determines what AHBs do
differently, it might be possible to breed that desirable trait into
EHBs.By J. Kim
Kaplan, Agricultural Research Service Information Staff.
This research is part of Crop Production, an ARS National
Program (#305) described on the World Wide Web at
To reach scientists mentioned in this story, contact
Kim Kaplan, USDA-ARS
Information Staff, 5601
Sunnyside Ave., Beltsville, MD 20705-5128; phone (301) 504-1637, fax (301)
"What's Buzzing with Africanized Honey Bees?" was published
in the March
2004 issue of Agricultural Research magazine.