HYBRID (see text)
Africanized honey bees (also spelled Africanised honey bees), known colloquially as "killer bees", are a hybrid of the Western honey bee species, (Apis mellifera), produced originally by cross-breeding of the African honey bee A. m. scutellata, with various European honey bees such as the Italian bee A. m. ligustica and the Iberian bee A. m. iberiensis. The African honey bee was first introduced to Brazil in the 1950s in an effort to increase honey production, but in 1957, 26 swarms accidentally escaped quarantine and since then have spread throughout South and Central America and arrived in North America in 1985.
- 1 History
- 2 Geographic spread throughout North America
- 3 Foraging behavior
- 4 Morphology and genetics
- 5 Consequences of selection
- 6 Impact on existing apiculture
- 7 References
- 8 Further reading
- 9 External links
There are currently 28 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 and be better adapted to tropical conditions (i.e., more productive) than the European strain of honey bee currently in use throughout North, Central and South America. The hives containing this particular Africanized 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. But, 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 swarms spread out and cross-bred with local European colonies; their descendants have since spread throughout the Americas. Because their movement through South and Central America was rapid and largely unassisted by humans, Africanized bees have earned the reputation of being one of the most successful biologically invasive species of all time.
The first Africanized bees in the US were discovered in 1985 in the San Joaquin Valley of California, most likely having hitched a ride on a Venezuelan oil tanker. 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.
Despite the fact that Africanized 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 clear evidence that they are superior honey producers and pollinators.
The major differences between Africanized and other Western bee types are:
- Tends to swarm more frequently and go farther than other types of honey bees.
- Is more likely to migrate as part of a seasonal response to lowered food supply.
- Is more likely to "abscond"—the entire colony leaves the hive and relocates—in response to stress.
- Has greater defensiveness when in a resting swarm, compared to other honey bee types.
- Lives more often in ground cavities than the European types.
- Guards the hive aggressively, with a larger alarm zone around the hive.
- Has a higher proportion of "guard" bees within the hive.
- Deploys in greater numbers for defense and pursues perceived threats over much longer distances from the hive.
- Cannot survive extended periods of forage deprivation, preventing introduction into areas with harsh winters or extremely dry late summers.
Geographic spread throughout North America
African honeybees are considered an invasive species in the Americas. 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, Nevada, New Mexico, Florida, and southern California. Their expansion stopped for a time at eastern Texas, possibly due to the large population of honey bee hives in the area. However, discoveries of the Africanized bees in southern Louisiana indicate this subspecies 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 Louisiana 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. In 2012 state officials reported that a colony was found for the first time in a bee keepers colony in Monroe County, eastern Tennessee. In June 2013, 62-year old Larry Goodwin of Moody, TX was killed by a swarm of bees.
In tropical climates they effectively out-compete 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 continue to interbreed with European honeybees. In a study conducted in Arizona in 2004 it was observed that swarms of Africanized bees were capable of taking 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 African bees dominate, a mix of African and European bees is present, or only non-African bees are found, as in the southern portions of 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 the Africanized honey bee in Central America is threatening the ancient art of keeping Melipona stingless bees in log gums even though they do not interbreed or directly compete with the each other. The honey production from a single hive of Africanized bees can be 100 kg annually and far exceeds the much smaller 3 - 5 kg of the various Melipona stingless species. Thus economic pressures are forcing beekeepers to switch from the traditional bees of their ancestors to the new reality of the Africanized honey bee. Whether this will lead to their extinction is unknown, but they are well adapted to exist in the wild, and as well there are a number of indigenous plants that the Africanized honey bees do not visit, so their fate remains to be seen.
Africanized honey bees have a set of characteristics with respect to foraging behavior. Africanized honey bees begin foraging at young ages and harvest a greater quantity of pollen with respect to their European counterparts (Apis mellifera.) This may be linked to the high reproductive rate of the Africanized honey bee which requires pollen to feed the 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.
Variation in honey bee proboscis extension response
Honey bee sensitivity to different concentrations of sucrose is determined by a reflex known as the proboscis extension response or 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) forage at older ages and harvest less pollen and more concentrated nectar. The differences in resources emphasized during harvesting are a result of the fact that the European honey bee is sensitive to sucrose at higher concentrations.
Evolution of foraging behavior in honey bees
The differences in a variety of behaviors between different species of honey bee are the result of a directional selection that acts upon several foraging behavior traits as a common entity. Selection in natural populations of honey bee 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.”
There are multiple ways of considering the cause of directional selection on this set of foraging behaviors in honey bees. A proximate factor is one that is developmental and influential on behavior within the lifetime of an organism. Neurological and developmental differences lead to directional selection and changes in the set of foraging behaviors between generations of honey bees. Levels of stress as measured by levels of octopamine is one such contributing developmental factor.
An ultimate factor is one that explains long term evolutionary advantages of behavior in an organism. Proboscis extension response to different concentrations of sucrose is a genotypic trait; the genes vary with respect to the sucrose concentration level at which proboscis extension response is manifested. Natural selection is able to directly shift the set of foraging behaviors by operating on the distribution of these genes in the honey bee population.
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 like concentrated nectar will not be able to sustain themselves in harsher environments. The noted PER 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. While the native African scutellata are smaller, and build smaller comb cells than the European bees, their hybrids are not smaller. Africanized bees have slightly shorter wings, which can only be recognized reliably by performing a statistical analysis on micro-measurements of a substantial sample. One problem with this test is that there are also other subspecies, such as Apis mellifera iberiensis, which have shorter wings. This trait is thought to derive from ancient hybrid haplotypes thought to have links to evolutionary lineages from Africa. Some belong to Apis mellifera intermissa but others have an indeterminate origin; the Egyptian honeybee (Apis mellifera lamarckii), present in small numbers in the southeastern United States, 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 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.
The Western honey bee is native to the continents of Europe, Asia, and Africa. As of the early 1600s, the insect was introduced to North America, with subsequent introductions of other European subspecies two centuries later. Since then, they have spread throughout the Americas. The 28 subspecies can be assigned to one of four major branches based on work by Ruttner and subsequently confirmed by analysis of mitochondrial DNA. African subspecies are assigned to branch A, northwest European subspecies to branch M, southwest European subspecies to branch C, and Mideast subspecies to branch O. The subspecies are grouped and listed. There are still regions with localized variations that may become identified subspecies in the near future, such as A. m. pomonella from the Tian Shan mountains, which would be included in the Mideast subspecies branch.
The Western honey bee is the third insect to have its genome mapped, and is unusual in having very few transposons. According to the scientists who analyzed its genetic code, the western honey bee originated in Africa and spread to Eurasia in two ancient migrations. They have also discovered that the number of genes in the honey bees related to smell outnumber those for taste. The genome sequence revealed several groups of genes, particularly the genes related to circadian rhythms, were closer to vertebrates than other insects. Genes related to enzymes that control other genes were also vertebrate-like.
Besides, A. m. iberica haplotype is present in the honey bees of the western United States, Mexico and South America, where the honey bees are not native and they were introduced from Spain during the conquest of America, from populations with African haplotypes, whose origin is indeterminate. Apis mellifera iberica is having hybridization between the north of African and European bees, Apis mellifera mellifera, and Apis mellifera intermissa. Presents six haplotypes different, five of them correspond to an evolutionary lineage from Africa and one from Western Europe. From this, infer the hybrid nature of this subspecies, is similar to that of African populations in the number of alleles detected and the values of genetic diversity. Additionally A.m.intermissa genoma, present in A.m.iberica belongs to a group shown by experiment to have similar mtDNA, this including A. m. monticola, A. m. scutellata, A. m. adansonii and A. m. capensis.
Several researchers and beekeepers describe a general trait of the African subspecies Apis mellifera scutellata, classified by Lepeletier, 1836 - (African honey bee) Central and West Africa, which is absconding, where the Africanized honeybee colonies abscond the hive in times when food-stores are low, unlike the European colonies which tend to die in the hive.
There are two lineages of African subspecies Apis mellifera scutellata 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 have 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 beekeepers and the African stock is attributable to both selective breeding and natural selection. By selecting only the most gentle, non-defensive races, beekeepers have, over centuries, eliminated the more defensive races and created a number of subspecies suitable for apiculture. The most common race used in Europe and the United States today is the Italian bee, Apis mellifera ligustica, which has been used for over a thousand years in some parts of the world and in the Americas since the arrival of the European colonists. In fact those first bees were dubbed "the white mans fly" by native Americans, as they tended to precede colonists as they moved west.
But in central and southern Africa there was formerly no tradition of beekeeping, only bee robbing which effectively destroys a hive in order to harvest the honey, pollen and larvae. In addition the bees have had to adapt to the environment of sub-Saharan Africa, surviving prolonged droughts and having to defend themselves against aggressive insects such as ants and wasps, as well as voracious animals like the honey badger, that will destroy a hive that is not sufficiently defensive. This eventually led to the opposite extreme, a race of highly defensive bees unsuitable by a number of metrics for domestic use.
Africanized bees are characterized by far greater defensiveness than European honey bees. They are more likely to attack a perceived threat and, when they do so, attack relentlessly and in larger numbers. Also, they have been known to pursue a perceived threat for a distance of well over 500 meters. This aggressively protective behavior, termed hyper-defensive behavior by scientists, has earned them the nickname "killer bees", an unfortunate misnomer which has caused the public to misguidedly believe that "killer bees" actually seek out and attack victims for no reason other than sheer ferocity. And while over the past decades several deaths in North America can be directly attributed to Africanized bee attacks (as differentiated from deaths caused by an allergic reaction to a single or few bee stings), a person is still far more likely to be killed by lightning, or even a pet dog, than an attack by Africanized bees.
The venom of an Africanized bee is the same as that of a European honey bee, but since the former tends to sting in far greater numbers, the number of deaths from them are naturally greater than from European honey bees. However, allergic reaction to bee venom from any bee can kill a person, and so it is difficult to estimate with any accuracy how many more people have died due strictly to the presence of Africanized bees. Most encounters with Africanized bees occur when feral colonies take up residence near human habitation and then are accidentally discovered. Local beekeepers can greatly reduce this problem by trapping and removing these colonies and then killing the queen and replacing her with one from a gentler breed stock. But if the colony is too close to human habitation it is usually safer to simply destroy the colony in order to avoid the possibility of further attacks.
Beekeepers can also discover that their own colonies have suddenly become Africanized due to cross-breeding with a newly arrived feral colony of Africanized bees somewhere in the vicinity. This is most likely to happen when a hives queen is old or dies. The hive will produce a new queen who will then take a mating flight, and it is during this mating flight that drones from the wild Africanized colony will manage to mate with the European queen, almost always resulting in the Africanization of the existing colony. The beekeeper can address this problem by requeening, a term used for swapping out the old queen with a new, already fertilized one. As a prophylactic measure, the majority of beekeepers in North America do tend to requeen their hives annually to maintain strong and healthy colonies and also to avoid such unwanted and potentially dangerous hybridization.
The African bee is widely feared by the public, a reaction that has been amplified by sensationalist movies (such as The Swarm) and some of the media reports. Stings from African bees kill on average one or two people per year.
As the bee spreads through Florida, a densely populated state, officials worry that public fear may force misguided efforts to combat them.
|“||News reports of mass stinging attacks will promote concern and in some cases panic and anxiety, and cause citizens to demand responsible agencies and organizations to take action to help ensure their safety. We anticipate increased pressure from the public to ban beekeeping in urban and suburban areas. This action would be counter-productive. Beekeepers maintaining managed colonies of domestic European bees are our best defense against an area becoming saturated with AHB. These managed bees are filling an ecological niche that would soon be occupied by less desirable colonies if it were vacant.||”|
— Florida African Bee Action Plan
Africanized bees are not giant bees with deadly stings. The sting of the Africanized bee is no more potent than any other variety of honey bee, and although they are similar in appearance to European bees, they actually tend to be slightly smaller and darker in color. Africanized bees do not roam the countryside looking for people to attack. It's true that they are more dangerous because they are more easily provoked, quicker to attack in greater numbers, and then pursue the perceived threat farther, sometimes for up to half mile or more. While studies have shown that Africanized bees can infiltrate European bee colonies and then kill and replace their queen (thus usurping the hive), this is less common than other methods. Wild and managed colonies will sometimes be seen to fight over honey stores during the dearth (periods when plants are not flowering), but this behavior should not be confused with the aforementioned activity. The most common way that a European hive will become Africanized is through cross-breeding during a new queens mating flight. Studies have consistently shown that Africanized drones are more numerous, stronger and faster than their European cousins and are therefore able to out-compete them during these mating flights. The results of mating between Africanized drones and European queens is almost always Africanized offspring.
Queen management in Africanized bee areas
In areas where Africanized bees are well established, it has been found that a purchased and pre-fertilized (i.e. mated) European queen can be used to maintain a hives European genetics and behavior. However this practice can be expensive since these queens must be purchased and shipped from breeder apiaries which are completely free of Africanized bees, such as in northern U.S. states or Hawaii. As such this is generally not practical for most commercial beekeepers outside of the U.S. and one of the main reasons why Central and South American beekeepers have had to learn to manage and work with the existing Africanized honey bee. Any effort to cross-breed virgin European queens with Africanized drones will always result in some or all of the offspring exhibiting Africanized traits. This is the reason why, having started with only 26 escaped swarms in 1957, that nearly 6 decades later there does not appear to be a lessening to any noticeable degree of the typical Africanized characteristics. In fact some experts in the field think that calling these bees a hybrid or Africanized may be incorrect, and that what you really have are simply African bees.
Impact on existing apiculture
In areas of suitable temperate climate, the survival traits of Africanized colonies help them outperform European honey bee colonies. Africanized bees also display what could be called a superior work ethic. They are consistently up and out of the hive earlier, often at the crack of dawn, while their seemingly lazier European cousins are still tucked snugly inside their hives. They also return later and basically work under conditions that often keep European bees hive-bound. That's why they have gained a well-deserved reputation as superior honey producers, and those beekeepers who have learned to adapt their management techniques now seem to prefer them to their European counterparts. It is also becoming apparent that Africanized bees have another advantage over European bees in that they seem to show a higher resistance to several health issues including parasites such as the Varroa mite, some fungal diseases like chalkbrood and even the mysterious colony-collapse disorder which is currently plaguing beekeepers. As such, despite all the negatives, it is possible that the Africanized honey bee might actually end up being a boon to the apiculture industry.
Gentle Africanized bees
Not all Africanized hives display the typical hyper-defensive behavior, which may provide bee breeders a point to begin breeding a gentler stock. Work has been done in Brazil towards this end, but as mentioned previously, in order to maintain these traits, it is necessary to develop a queen breeding and mating facility in order to requeen colonies and so prevent reintroduction of unwanted genetics or characteristics through unintended cross-breeding with feral colonies. Also while bee incidents are much less common than they were during the first wave of Africanized bee colonization, this can be largely attributed to modified and improved bee management techniques. Prominent among these are locating bee-yards much further from human habitation, creating barriers to keep livestock at enough of a distance to prevent interaction, and education of the general public to teach them how to properly react when feral colonies are encountered and what resources to contact. Knowledge is the key and is why the Africanized bee is considered the bee of choice for beekeeping in Brazil.
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|Wikimedia Commons has media related to Apis mellifera scutellata.|
- Africanized Bee Fact Sheet includes information on biology, habits, habitat and prevention tips
- U.S. Department of the Interior, Biological Resources Discipline
- Barry Sergeant, keeper of "killer bees"[dead link]
- African BEES: They are here to stay. See how these bees spread to Florida.
- African honey bee on the UF / IFAS Featured Creatures Web site
- Texas A&M University African Honey Bee Information Site[dead link]
- CISR: Center for Invasive Species Research Fact Sheet on African Honey Bees[dead link]
- Species Profile- Africanized Honeybee (Apis mellifera scutellata Lepeletier), National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for Africanized Honeybee.
- The short film Africanized Bee Alert (1985) is available for free download at the Internet Archive [more]