Africanized Honey Bees?
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What’sWhat’s BuzzingBuzzing withwith 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 Iwanted to know what they would be fac- would reach a steady state of hybridiza- ing as Africanized honey bees began to tion, because we knew the two groups SCOTT BAUER (K11074-1) 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 dominating the environment. European honey bees (EHBs), because 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.” would interbreed with existing feral metry that increase with hybridization 4 Agricultural Research/March 2004 348938 4 2/6/04, 4:23 AM First found in southern WHERE ARE Texas in 1990, Africanized honey bees are now found in most THEY NOW ? 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 BAUER (K11071-1) Southwest, the U.S. inseminate a queen with a 50-50 mix of matrilines as well as patrilines. “In 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 348938 5 2/12/04, 12:19 PM 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 where AHBs would predominate, a SCOTT BAUER (K11073-1) northern zone where EHBs would maintain a climatic advantage, and a large transitional zone between the two.