Mar. 31, 1998
WEST LAFAYETTE, Ind. -- The gene for aggressive stinging behavior in Africanized honey bees -- the so-called "killer bees" -- has been identified by a group of scientists at three institutions.
Greg Hunt, a bee specialist with the Purdue University Department of Entomology and principal investigator on the research project, says finding the mean gene in honey bees "may help us reduce the occurrence of Africanized bees and prevent the spread of the gene to other bee colonies."
Keeping the gene in check is important for much of U.S. agriculture, and not just for honey producers, because 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.
Although Africanized honey bees are rarely the "killer bees" of 1970s Movie-of-the-Week fame, they are decidedly more aggressive than their European cousins. Research conducted in Venezuela in 1982 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.
According to entomologists, though, Africanized honey bees aren't bad, just misunderstood: "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."
Through this process 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."
Hunt says these findings may allow breeders and scientists to reduce the spread of the Africanized traits in the Western Hemisphere.
"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."
The research is published in the March issue of the scientific journal Genetics. The research was funded by the U.S. Department of Agriculture, the National Institutes of Health, and the California Department of Food and Agriculture.
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.
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."
Also, 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.
This would be bad news for beekeepers, because the Africanized honey bees are quite troublesome. This could cause even more beekeepers to quit their declining ranks. Among the problems:
- Africanized bees bring concerns about liability if they sting neighbors or livestock or pets. "In the tropics many people have stopped raising bees because of concerns about liability," Hunt says.
- Honey bees lose their stingers after an attack, which causes them to die. A very aggressive colony of bees can lose thousands of its bees when they stage an attack.
- The aggressiveness of Africanized bees forces beekeepers to don protective clothing, which is hot, uncomfortable and cumbersome.
- Africanized honey bees produce less honey per hive than European breeds.
- Finally, the Africanized bees are more likely to abscond from the bee keepers when the conditions aren't to their liking. "The Africanized bees are a very nervous breed," Hunt says.
Editor's note: The original news release, with related material and images, can be found at http://news.uns.purdue.edu/html4ever/9804.Hunt.gene.html
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