West
Lafayette, IND (3/30/98)- The discovery of a "mean gene" in Africanized
honey bees could provide the basis for reducing the diaspora of these 'killer'
bees, now buzzing their way into California.
Researchers at three institutions collaborated in a successful search
for the gene for aggressive stinging behavior in the Africanized
honey bees. Finding the 'mean gene' "may help us reduce the occurrence
of Africanized bees and prevent the spread of the gene to other bee colonies,"
said Greg Hunt, a bee specialist with the Purdue University Department
of Entomology and principal investigator on the project.
Graphic: Greg Hunt checks
a bee hive at a Purdue research facility.
Controlling the spread of the aggresive bees from South America is critical
for the survival of U.S. agriculture, not to mention honey producers. One-third
of the food produced in the United States comes from plants pollinated
by honey bees. Because of fatal infestations of two parasites, almost all
honey bees in North America now are raised by
beekeepers. Already many beekeepers in Mexico have stopped keeping
bee hives because of the eager stingers, he noted.
Africanized honey bees are a genetic variant of our own European-origin
honey bees. The interlopers are considerably more aggressive. Research conducted in Venezuela found
that Africanized honey bees will attack a visual stimulus 20 times faster
than European honey bees and that when they attack they deposit about eight
times as many stingers in the first 30 seconds.
Africanized honey bees aren't bad, just misunderstood, say entomologists:
"It seems like aggression when a bee stings you, but we call it defensive
behavior," Hunt says. "Different insects use various methods to protect
themselves from predators. Bee stings are a response to predation by mammals
-- bee venom is specialized for causing pain in vertebrates."
Hunt and colleagues Robert E. Page of the University of California-
Davis and Ernesto Guzman-Novoa
of Mexico's agricultural research service identified the mean gene
by measuring the speed and intensity
of stinging behavior in 162 colonies of hybrid bees. They then located
gene markers on the chromosomes
of the aggressive hybrid bees and compared the genes with those of
non-aggressive hybrid bees.
"We made a genetic map of the honey bee using the same techniques used
in crop genetics, a technique
called quantitative trait locus mapping," Hunt says. "This process
hasn't been used much in insects. But if
you have markers for the genes, we can do what the crop geneticists
are doing and selectively breed for
gentle bees."
The scientists identified five genes that appear to have some link to
the aggressive behavior, and one of these genes was found to have a much
greater effect on the tendency to sting. "We have also mapped genes that
affect levels of alarm pheromone," Hunt says. "These genes are completely
independent of stinging behavior."
These findings may allow breeders and scientists to reduce the spread
of the Africanized traits in the Western Hemisphere, he ntoes:
"We are developing specific genetic markers that could predict the probability
of queens having the
African version of stinging genes so it will be easier for breeders
to avoid using these queen bees," Hunt
says. "Ultimately it might be possible to clone the gene through map-
based cloning so that we can better
understand how this gene affects stinging behavior."
Background
Africanized bees are just one of several subspecies of honey bees. They
were introduced to the Western
Hemisphere by an accidental release from a Brazilian geneticist in
1956 and spread rapidly through South
and Central America. Since then they have spread steadily north, entering
Mexico in 1988. By 1991,
almost 100 percent of the honey bees in Mexico carried the aggressiveness
gene.
Graphic: Africanized honey
bees have spread through Mexico and into the southern United States. (Purdue
Agricultural Communications)
The Africanized bees reached the United States in 1991 and are now found
in parts of Texas, New
Mexico, Arizona and southern California. There the spread of the Africanized
bees has stalled.
"Although the front of the migration has slowed down, it shouldn't
be any problem for the bees to go
across the Louisiana coast or go farther north in California," Hunt
says. "We don't know why they
haven't gone there already."
Even without further migration, the Africanized bees still could threaten
the bee population throughout
North America. "In the tropics the aggressiveness trait is a desired
one; we don't know if it will be a
dominant trait in temperate areas, too," Hunt says. "If it is, the
aggressiveness trait could be introduced in
northern areas in European bees even if the subspecies of Africanized
bees doesn't expand its territory."
The mechanism for spreading the trait is already in place. Because of
fatal infestations of two
parasites, there are almost no wild bees left in North America. Virtually
all honey bees are raised by
beekeepers who buy their queen bees each spring from large breeders
in the southern states near the
regions where Africanized honey bees have invaded. These queens could
acquire the gene for
aggressive behavior and spread the trait to other regions of the country,
Hunt says.
The research appears in the March 1998 issue of the scientific journal
Genetics.
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