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April 1998

'Mean gene' found in Africanized honey bees

WEST LAFAYETTE, Ind. -- A gene that has a large effect on the aggressive stinging behavior in Africanized honey bees -- the so-called "killer bees" -- has been identified by a group of scientists at three institutions.

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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 understand what makes Africanized bees so aggressive."

Hunt and colleagues Robert E. Page of the University of California-Davis and Ernesto Guzman-Novoa of Mexico's agricultural research service located the mean gene by measuring the speed and intensity of stinging behavior in 162 colonies of hybrid bees. They then located DNA markers on the chromosomes of the aggressive hybrid bees and compared the genes with those of nonaggressive hybrid bees.

Now that they have mapped the gene in the honey bee genome, the researchers say the next step would be to isolate the gene for further study. "We've found a place on a chromosome where this gene or genes may be, but we hope in time to be able to localize it better," Page says. "Someday we may actually be able to isolate and characterize the gene and find out how the two versions of the gene differ."

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Hunt says the finding will lead to markers for the aggressiveness trait. "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," he 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.

"We made a genetic map of the honey bee using the same techniques used in crop genetics, a technique called quantitative trait locus mapping. This process hasn't been used much in insects. But if we 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. "All but one of these genes are completely independent of 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.

Having gentle bees 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. Most bees in the United States are kept by beekeepers because two fatal infestations of parasites have wiped out most of the native bees. In areas where they have invaded, Africanized bees cause many beekeepers to quit the business -- already many beekeepers in Mexico have stopped keeping bee hives because of the eager stingers.

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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."

Africanized bees are just one of many 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 feral honey bees in Mexico carried the African bee DNA.

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 defensive behavior gives the bees an advantage; we don't know if it will be an advantage in temperate areas, too," Hunt says. "If it is, the tendency to be aggressive could be introduced in northern areas in European bees even if the Africanized bees do not expand their territory."

This would be bad news for beekeepers, because the Africanized honey bees are quite troublesome. Among the problems:

  • Africanized bees bring concerns about liability if they sting neighbors or livestock or pets.
  • 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.

Sources: Greg Hunt, (765) 494-4605; e-mail, ghunt@entm.purdue.edu
Robert Page, (916) 752-5455; e-mail repage@ucdavis.edu;
Web, http://entomology.ucdavis.edu/faculty/page.html
Writer: Steve Tally, (765) 494-9809; e-mail, tally@aes.purdue.edu;
Web, http://www.agcom.purdue.edu/AgCom/homepages/tally/
Purdue News Service: (765) 494-2096; e-mail, purduenews@purdue.edu

NOTE TO JOURNALISTS: A copy of the Genetics article is available for background from the Purdue News Service, (765) 494-2096. Three color photographs also are available: "Hunt.Hive" shows researcher Greg Hunt working with a bee hive; "Hunt.Attack" shows the Africanized bees during a swarming attack; and "Hunt.Map" is a map illustrating the expanding territory of the Africanized bees.

PHOTO ONE:
Greg Hunt, honey bee Cooperative Extension Service specialist at Purdue, checks a bee hive at a Purdue research facility. Hunt and two other researchers have identified a gene in Africanized honey bees that causes their aggressive stinging behavior. (Purdue Agricultural Communications photo by Greg Hunt.)
Color photo, electronic transmission, and Web and ftp download available. Photo ID: Hunt.Hive
Download here.

PHOTO TWO:
Africanized honey bees attack more aggressively than their European cousins, as this Mexican beekeeper discovered. (Purdue Agricultural Communications photo by Ernesto Guzman-Novoa.)
Color photo, electronic transmission, and Web and ftp download available. Photo ID: Hunt.Attack
Download here.

PHOTO THREE:
Africanized honey bees, known popularly as killer bees, have spread through Mexico and into the southern United States. (Purdue Agricultural Communications graphic by Christie Williams and Greg Hunt.)
Color map, electronic transmission, and Web and ftp download available. Photo ID: Hunt.Map
Download here.

ABSTRACT

Quantitative trait loci for honey bee stinging behavior and body size

Greg J. Hunt, Purdue University, West Lafayette, Ind.; Ernesto Guzman-Novoa, INIFAP/SAGAR, Mexico City; and Robert E. Page Jr., University of California, Davis, Calif.

A study was conducted to identify quantitative trait loci (QTLs) that affect colony-level stinging behavior and individual body size of honey bees. An F1 queen was produced from a cross between two honey bees, one of European origin and one descended from an African subspecies. Haploid drones from the hybrid queen were individually backcrossed to sister European queens to produce 172 colonies with backcross workers that were evaluated for tendency to sting. RAPD markers were scored from the haploid drone fathers of these colonies. Wings of workers and drones were used as a measure of body size because Africanized bees in the Americas are smaller than European bees. Standard interval mapping and multiple QTL models were used to analyze data. One possible QTL was identified with a significant effect on tendency to sting (LOD 3.57). Four other suggestive QTLs were also observed (about LOD 1.5). Possible QTLs also were identified that affect body size and were unlinked to defensive-behavior QTLs. Two of these were significant (LOD 3.54 and 5.15).


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