Hybrid species of bee
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The Africanized bee, also known as the Africanized honey bee (AHB) and colloquially as the "killer bee", is a hybrid of the western honey bee ("Apis mellifera"), produced originally by crossbreeding of the East African lowland honey bee ("A. m. scutellata") with various European honey bee subspecies such as the Italian honey bee ("A. m. ligustica") and the Iberian honey bee ("A. m. iberiensis").
The East African lowland honey bee was first introduced to Brazil in 1956 in an effort to increase honey production, but 26 swarms escaped quarantine in 1957. Since then, the hybrid has spread throughout South America and arrived in North America in 1985. Hives were found in south Texas in the United States in 1990.
Africanized honey bees are typically much more defensive, react to disturbances faster, and chase people further () than other varieties of honey bees. They have killed some 1,000 humans, with victims receiving 10 times more stings than from European honey bees. They have also killed horses and other animals.
History.
There are 29 recognized subspecies of "Apis mellifera" based largely on geographic variations. All subspecies are cross-fertile. Geographic isolation led to numerous local adaptations. These adaptations include brood cycles synchronized with the bloom period of local flora, forming a winter cluster in colder climates, migratory swarming in Africa, enhanced (long-distance) foraging behavior in desert areas, and numerous other inherited traits.
The Africanized honey bees in the Western Hemisphere are descended from hives operated by biologist Warwick E. Kerr, who had interbred honey bees from Europe and southern Africa. Kerr was attempting to breed a strain of bees that would produce more honey in tropical conditions than the European strain of honey bee then in use throughout North, Central and South America. The hives containing this particular African subspecies were housed at an apiary near Rio Claro, São Paulo, in the southeast of Brazil, and were noted to be especially defensive. These hives had been fitted with special excluder screens (called queen excluders) to prevent the larger queen bees and drones from getting out and mating with the local population of European bees. According to Kerr, in October 1957 a visiting beekeeper, noticing that the queen excluders were interfering with the worker bees' movement, removed them, resulting in the accidental release of 26 Tanganyikan swarms of "A. m. scutellata". Following this accidental release, the Africanized honey bee swarms spread out and crossbred with local European honey bee colonies.
The descendants of these colonies have since spread throughout the Americas, moving through the Amazon basin in the 1970s, crossing into Central America in 1982, and reaching Mexico in 1985. Because their movement through these regions was rapid and largely unassisted by humans, Africanized honey bees have earned the reputation of being a notorious invasive species. The prospect of killer bees arriving in the United States caused a media sensation in the late 1970s, inspired several horror movies, and sparked debate about the wisdom of humans altering entire ecosystems.
The first Africanized honey bees in the U.S. were discovered in 1985 at an oil field in the San Joaquin Valley of California. Bee experts theorized the colony had not traveled overland but instead "arrived hidden in a load of oil-drilling pipe shipped from South America." The first permanent colonies arrived in Texas from Mexico in 1990. In the Tucson region of Arizona, a study of trapped swarms in 1994 found that only 15 percent had been Africanized; this number had grown to 90 percent by 1997.
Characteristics.
Though Africanized honey bees display certain behavioral traits that make them less than desirable for commercial beekeeping, excessive defensiveness and swarming foremost, they have now become the dominant type of honey bee for beekeeping in Central and South America due to their genetic dominance as well as ability to out-compete their European counterpart, with some beekeepers asserting that they are superior honey producers and pollinators.
Africanized honey bees, as opposed to other Western bee types:
North American distribution.
Africanized honey bees are considered an invasive species in the Americas. As of 2002, the Africanized honey bees had spread from Brazil south to northern Argentina and north to Central America, Trinidad (the West Indies), Mexico, Texas, Arizona, Nevada, New Mexico, Florida, and southern California. In June 2005, it was discovered that the bees had spread into southwest Arkansas. Their expansion stopped for a time at eastern Texas, possibly due to the large population of European honey bee hives in the area. However, discoveries of the Africanized honey bees in southern Louisiana show that they have gotten past this barrier, or have come as a swarm aboard a ship.
On 11 September 2007, Commissioner Bob Odom of the Louisiana Department of Agriculture and Forestry said that Africanized honey bees had established themselves in the New Orleans area. In February 2009, Africanized honey bees were found in southern Utah. The bees had spread into eight counties in Utah, as far north as Grand and Emery Counties by May 2017.
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. In 2012, Tennessee state officials reported that a colony was found for the first time in a beekeeper's colony in Monroe County in the eastern part of the state. In June 2013, 62-year-old Larry Goodwin of Moody, Texas, was killed by a swarm of Africanized honey bees.
In May 2014, Colorado State University confirmed that bees from a swarm which had aggressively attacked an orchardist near Palisade, in west-central Colorado, were from an Africanized honey bee hive. The hive was subsequently destroyed.
In tropical climates they effectively out-compete European honey bees and, at their peak rate of expansion, they spread north at almost two kilometers (about 1¼ 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 could not prevent the bees' expansion. Current knowledge of the genetics of these bees suggests that such a strategy, had it been tried, would not have been successful.
As the Africanized honey bee migrates further north, colonies continue to interbreed with European honey bees. In a study conducted in Arizona in 2004 it was observed that swarms of Africanized honey bees could take over weakened European honey bee hives by invading the hive, then killing the European queen and establishing their own queen. There are now relatively stable geographic zones in which either Africanized honey bees dominate, a mix of Africanized and European honey bees is present, or only non-Africanized honey bees are found, as in the southern portions of South America or northern North America.
African honey bees 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 not enough stores to survive the winter. Thus Africanized honey 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 Africanized honey 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 the Africanized honey bee in Central America is threatening the traditional craft of keeping "Melipona" stingless bees in log gums, although they do not interbreed or directly compete with each other. The honey production from an individual hive of Africanized honey bees can be as high as . This value exceeds the much smaller of the various "Melipona" stingless bee species. Thus economic pressures are forcing beekeepers to switch from the traditional stingless bees to the new reality of the Africanized honey bee. Whether this will lead to the extinction of the former is unknown, but they are well adapted to exist in the wild, and there are a number of indigenous plants that the Africanized honey bees do not visit, so the fate of the "Melipona" bees remains to be seen.
Foraging behavior.
Africanized honey bees begin foraging at young ages and harvest a greater quantity of pollen compared to their European counterparts ("Apis mellifera ligustica"). This may be linked to the high reproductive rate of the Africanized honey bee, which requires pollen to feed its greater number of larvae. Africanized honey bees are also sensitive to sucrose at lower concentrations. This adaptation causes foragers to harvest resources with low concentrations of sucrose that include water, pollen, and unconcentrated nectar. A study comparing "A. m. scutellata" and "A. m. ligustica" published by Fewell and Bertram in 2002 suggests that the differential evolution of this suite of behaviors is due to the different environmental pressures experienced by African and European subspecies.
Proboscis extension responses.
Honey bee sensitivity to different concentrations of sucrose is determined by a reflex known as the proboscis extension response (PER). Different species of honey bees that employ different foraging behaviors will vary in the concentration of sucrose that elicits their proboscis extension response.
For example, European honey bees ("Apis mellifera ligustica") forage at older ages and harvest less pollen and more concentrated nectar. The differences in resources collected during harvesting are a result of the European honey bee's sensitivity to sucrose at higher concentrations.
Evolution.
The differences in a variety of behaviors between different species of honey bees are the result of a directional selection that acts upon several foraging behavior traits as a common entity. Selection in natural populations of honey bees show that positive selection of sensitivity to low concentrations of sucrose are linked to foraging at younger ages and collecting resources low in sucrose. Positive selection of sensitivity to high concentrations of sucrose were linked to foraging at older ages and collecting resources higher in sucrose. Additionally of interest, "change in one component of a suite of behaviors appear[s] to direct change in the entire suite."
When resource density is low in Africanized honey bee habitats, it is necessary for the bees to harvest a greater variety of resources because they cannot afford to be selective. Honey bees that are genetically inclined towards resources high in sucrose, such as concentrated nectar, will not be able to sustain themselves in harsher environments. The noted to low sucrose concentration in Africanized honey bees may be a result of selective pressure in times of scarcity when their survival depends on their attraction to low quality resources.
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 between a "killer" honey bee and an ordinary honey bee. Government and scientific documents prefer "Africanized honey bee" as an accepted scientific taxon.
Morphological tests.
Although the native East African lowland honey bees ("Apis mellifera scutellata") are smaller and build smaller comb cells than the European honey bees, their hybrids are not smaller. Africanized honey bees have slightly shorter wings, which can only be recognized reliably by performing a statistical analysis on micro-measurements of a substantial sample.
One of the problems with this test is that there are other subspecies, such as "A. m. iberiensis", which also have shortened wings. This trait is hypothesized to derive from ancient hybrid haplotypes thought to have links to evolutionary lineages from Africa. Some belong to "A. m. intermissa", but others have an indeterminate origin; the Egyptian honeybee ("Apis mellifera lamarckii"), present in small numbers in the southeastern U.S., has the same morphology.
DNA tests.
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 only allows one to detect Africanized colonies that have Africanized queens and not colonies where a European queen has mated with Africanized drones. A test based on single nucleotide polymorphisms was created in 2015 to detect Africanized bees based on the proportion of African and European ancestry.
Western variants.
The western honey