Africanized honey bees, known colloquially as "killer bees," are hybrids of the African honey bee, A. m. scutellata, with various European honey bees such as the Italian bee A. m. ligustica and A. m. iberiensis. These bees are far more aggressive than the European subspecies. Small swarms of AHBs are capable of taking over European honey beehives by invading the hive and establishing their own queen after killing the European queen.
The Africanized honey bee in the western hemisphere is directly descended from 26 Tanzanian queen bees (A. m. scutellata) accidentally released by a replacement bee-keeper in 1957 near Uberlândia, Minas Gerais State in the southeast of Brazil from hives operated by biologist Warwick E. Kerr, who had interbred honey bees from Europe and southern Africa. Hives containing these particular queens were noted to be especially defensive. Kerr was attempting to breed a strain of bees that would produce more honey and be better adapted to tropical conditions (i.e., more productive) than the European bees used in South America and southern North America. The hives the bees were released from had special excluder grates to prevent the larger queen bees and drones from getting out and mating with local (non-African) queens and drones. However, following the accidental release, the African queens and drones mated with local queens and drones, and their descendants have since spread throughout the Americas.
The African hybrid bees have become the preferred types of bee for beekeeping in Central America and in tropical areas of South America because of improved productivity. However, in most areas the African hybrid is initially feared because it tends to retain certain behavioral traits from its African ancestors that make it less desirable for domestic beekeeping. Specifically (as compared with the European bee types), the African bee:
As of 2002, the Africanized honeybees had spread from Brazil south to northern Argentina and north to Central America, Trinidad (West Indies), Mexico, Texas, Arizona, New Mexico, Florida, and southern California. Their expansion stopped for a time at eastern Texas, possibly due to the large number of European-bee beekeepers in the area. However, discoveries of the bees in southern Louisiana indicate this species of bee has penetrated this barrier, or has come as a swarm aboard a ship. In June 2005, it was discovered that the bees had penetrated the border of Texas and had spread into southwest Arkansas. On September 11, 2007, Commissioner Bob Odom of the Department of Agriculture and Forestry said that Africanized honey bees established themselves in the New Orleans area. In February 2009, Africanized honeybees were found in southern Utah. In October 2010, a 73-year-old man was killed by a swarm of Africanized honey bees while clearing brush on his south Georgia property, as determined by Georgia's Department of Agriculture. It is the first time state officials have recorded that such bees exist in Georgia.
In tropical climates they compete effectively against European bees and, at their peak rate of expansion, they spread north at a rate of almost two kilometers (about one mile) a day. There were discussions about slowing the spread by placing large numbers of docile European-strain hives in strategic locations, particularly at the Isthmus of Panama, but various national and international agricultural departments were unable to prevent the bees' expansion. Current knowledge of the genetics of these bees suggests that such a strategy, had it been attempted, would not have been successful.
As the Africanized honeybee migrates further north, colonies are interbreeding with European honeybees. There are now relatively stable geographic zones in which either African bees dominate, a mix of African and European bees is present, or only non-African bees are found (as in southern South America or northern North America).
African honeybees abscond (abandon the hive and any food store to start over in a new location) more readily than European honeybees. This is not necessarily a severe loss in tropical climates where plants bloom all year but in more temperate climates it can leave the colony with insufficient stores to survive the winter. Thus Africanized bees are expected to be a hazard mostly in the Southern States of the United States, reaching as far north as the Chesapeake Bay in the east. The cold-weather limits of the African bee have driven some professional bee breeders from Southern California into the harsher wintering locales of the northern Sierra Nevada and southern Cascade Range. This is a more difficult area to prepare bees for early pollination placement in, such as is required for the production of almonds. The reduced available winter forage in northern California means that bees must be fed for early spring buildup.
The arrival of African honeybees in Central America is a threat to the ancient art of keeping stingless bees in log gums even though they do not interbreed or directly compete with the stingless bees. The honey productivity of the African bees so far exceeds the productivity of the native stingless bees that economic pressures force beekeepers to switch. African honeybees are considered an invasive species in many regions.
Morphology and genetics
The popular term 'Killer bee' has only limited scientific meaning today because there is no generally accepted fraction of genetic contribution used to establish a cut-off. While the native African bees are smaller, and build smaller comb cells than the European bee, their hybrids are not smaller. They do have slightly shorter wings, which can be reliably recognized only by performing a statistical analysis on micro-measurements of a substantial sample. One problem with this test is that there is also an Egyptian bee, present in the southeastern United States, that has the same morphology. Currently testing techniques have moved away from external measurements to DNA analysis, but this means the test can only be done by a sophisticated laboratory. Molecular diagnostics using the mitochondrial DNA (mtDNA) cytochrome b gene can differentiate A. m. scutellata from other A. mellifera lineages, though mtDNA (which is strictly maternally-transmitted) only allows one to detect an Africanized colony that has an Africanized queen, and not colonies where a European queen has mated with Africanized drones.
There are two lineages of African bees in the Americas: actual matrilinial descendants of the original escaped queens and a much smaller number that are African through hybridization. The matrilinial descendants carry African mtDNA, but partially European nuclear DNA, while the bees that are African through hybridization carry European mtDNA, and partially African nuclear DNA. The matrilinial descendants are in the vast majority. This is supported by DNA analyses performed on the bees as they spread northwards; those that were at the "vanguard" were over 90% African mtDNA, indicating an unbroken matriline (Smith et al., 1989), but after several years in residence in an area interbreeding with the local European strains, as in Brazil, the overall representation of African mtDNA drops to some degree. However, these latter hybrid lines (with European mtDNA) do not appear to propagate themselves well or persist. Population genetics analysis of Africanized honey bees in the United States, using a materially inherited genetic marker, found 12 distinct mitotypes, and the amount of genetic variation observed supports the idea that there has been multiple introductions of AHB into the United States.
Consequences of selection
The chief difference between the European races or subspecies of bees kept by American beekeepers and the African stock is attributable to selective breeding. The most common race used in North America today is the Italian bee, Apis mellifera ligustica, which has been used for several thousand years in some parts of the world and in the Americas since the arrival of the early European colonists. Beekeepers have tended to eliminate the fierce strains, and the entire race of bees has thus been gentled by selective breeding.
In central and southern Africa, bees have had to defend themselves against other aggressive insects, as well as honey badgers, an animal that also will destroy hives if the bees are not sufficiently defensive. In addition, there was formerly no tradition of beekeeping, only bee robbing. When one wanted honey, one would seek out a bee tree and kill the colony, or at least steal its honey. The colony most likely to survive either animal or human attacks was the fiercest one. These hardy bees had to adapt to the hostile environment of sub-saharan Africa—surviving prolonged droughts and fighting for nectar. Thus the African bee has been naturally selected for ferocity.
African bees are characterized by greater defensiveness in established hives than European honey bees. They are more likely to attack a perceived threat and, when they do so, attack relentlessly in larger numbers. This aggressively protective behavior has been termed by scientists as hyper-defensive behavior. This defensiveness has earned them the nickname "killer bees," the aptness of which is debated. Over the decades, several deaths in the Americas have been attributed to African bees. The venom of an African bee is no more potent than that of a European honey bee, but since the former tends to sting in greater numbers, the number of deaths from them are greater than from the European honey bee. However, allergic reaction to bee venom from any bee can kill a person, and it is difficult to estimate how many more people have died due to the presence of African bees.
Most human incidents with African bees occur within two or three years of the bees' arrival and then subside. Beekeepers can greatly reduce this problem by culling the queens of aggressive strains and breeding gentler stock. Beekeepers keep A. m. scutellata in South Africa using common beekeeping practices without excessive problems.
The African bee is widely feared by the public, a reaction that has been amplified by sensationalist movies and some of the media reports. Stings from African bees kill 1–2 people per year in the United States.
As the bee spreads through Florida, a densely populated state, officials worry that public fear may force misguided efforts to combat them.
The much smaller and much more aggressive South American stingless bee Trigona spinipes does not interbreed and is known to kill or chase Africanized bees.
The sting of the Africanized Honey Bee is no more potent than your garden variety honey bee and they look pretty much the same. What makes AHBs more dangerous is that they are more easily provoked, quick to swarm, attack in greater numbers, and pursue their victims for greater distances. The AHB colony can remain agitated longer and may attack up to a quarter of a mile away from the hive.
Queen management in African bee areasIn Mexico, where African bees are well established, pollination beekeepers have found that a purchased and pre-bred non-African queen may be used to locally create a first generation of virgin queens that are then bred in an uncontrolled fashion with the local wild African drones. These first generation African queens produce worker bees that are manageable, not exhibiting the intense and massive defense reactions of subsequent generations. This offers a relatively economical method of safe local beekeeping conditions that would otherwise quickly lead to hazardous conditions.
Impact on existing apiculture
In areas of suitable temperate climate, the survival traits of African queens and colonies outperform western honey bee colonies. This competitive edge leads to the dominance of African traits. In Brazil, the African hybrids are known as Assassin Bees, for their habit of taking over an existing hive of European bees; this habit is most evident when the hive being attacked has a weakened queen, so not all hives are equally vulnerable, and overall rates of hive usurpation can reach 20%.
Gentle African bees
Not all African hives show overly defensive behavior; some colonies are quiet, which gives a beginning point for beekeepers to breed a gentler stock. This has been done in Brazil, where bee incidents are much less common than they were during the first wave of the African bees' colonization. Now that the African bee has been "re-domesticated," it is considered the bee of choice for beekeeping in Brazil.