Editing Africanized bee (section)

== 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.

[[File:Honey Bee takes Nectar.JPG|thumb|Compare ''[[Apis mellifera scutellata|A. m. scutellata]]'']]
One of the problems with this test is that there are other subspecies, such as ''[[Apis mellifera iberiensis|A. m. iberiensis]]'', which also have shortened wings. This trait is hypothesized to derive from ancient hybrid [[haplotype]]s thought to have links to evolutionary lineages from Africa. Some belong to ''[[Apis mellifera intermissa|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.<ref>{{cite journal |author1=Szalanski, A.L. |author2=McKern, J.A. |year=2007 |title= Multiplex PCR-RFLP diagnostics of the African honey bee (Hymenoptera: Apidae) |journal=Sociobiology |volume=50 |pages=939–945 |url=https://www.researchgate.net/publication/236783611}}</ref> A test based on single nucleotide polymorphisms was created in 2015 to detect Africanized bees based on the proportion of African and European ancestry.<ref>{{cite journal |doi=10.1111/1755-0998.12411 |pmid=25846634 |title=A SNP test to identify Africanized honeybees via proportion of 'African' ancestry |journal=Molecular Ecology Resources |volume=15 |issue=6 |pages=1346–55 |year=2015 |last1=Chapman |first1=Nadine C. |last2=Harpur |first2=Brock A. |last3=Lim |first3=Julianne |last4=Rinderer |first4=Thomas E. |last5=Allsopp |first5=Michael H. |last6=Zayed |first6=Amro |last7=Oldroyd |first7=Benjamin P.|hdl=2123/12853 |s2cid=5147394 |hdl-access=free }}</ref>

===Western variants===
The western honey bee is native to the continents of Europe, Asia, and Africa. As of the early 1600s, it was introduced to North America, with subsequent introductions of other European subspecies 200 years later.<ref>{{cite web |url=https://www.sciencedaily.com/releases/2006/12/061211220927.htm |title=Research upsetting some notions about honey bees |website=[[ScienceDaily]] |date=29 December 2006}}</ref> Since then, they have spread throughout the Americas. The 29&nbsp;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&nbsp;A, northwestern European subspecies to branch&nbsp;M, southwestern European subspecies to branch&nbsp;C, and Mideast subspecies to branch&nbsp;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 whose [[Gene mapping|genome has been mapped]], and is unusual in having very few [[transposon]]s. According to the scientists who analyzed its genetic code, the western honey bee originated in Africa and spread to Eurasia in two ancient migrations.<ref>{{Cite journal |doi=10.1126/science.1132772 |pmid=17068261 |title=Thrice out of Africa: Ancient and recent expansions of the honey bee, ''Apis mellifera'' |journal=Science |volume=314 |issue=5799 |pages=642–5 |year=2006 |last1=Whitfield |first1=C.W. |last2=Behura |first2=S.K. |last3=Berlocher |first3=S.H. |last4=Clark |first4=A.G. |last5=Johnston |first5=J.S. |last6=Sheppard |first6=W.S. |last7=Smith |first7=D.R. |last8=Suarez |first8=A.V. |last9=Weaver |first9=D. |last10=Tsutsui |first10=N.D. |bibcode=2006Sci...314..642W|s2cid=15967796 }}</ref> They have also discovered that the number of genes in the honey bee related to smell outnumber those for taste.<ref name='genome'>{{Cite journal |doi=10.1038/nature05260 |pmid=17073008 |title=Insights into social insects from the genome of the honeybee ''Apis mellifera'' |journal=Nature |volume=443 |issue=7114 |pages=931–949 |year=2006 | last1 = Weinstock | first1 = G. M. | last2 = Robinson | first2 = G. E. | last3 = Gibbs | first3 = R. A. | last4 = Worley | first4 = K. C. | last5 = Evans | first5 = J. D. | last6 = Maleszka | first6 = R. | last7 = Robertson | first7 = H. M. | last8 = Weaver | first8 = D. B. | last9 = Beye | first9 = M. | last10 = Bork | first10 = P. | last11 = Elsik | first11 = C. G. | last12 = Hartfelder | first12 = K. | last13 = Hunt | first13 = G. J. | last14 = Zdobnov | first14 = E. M. | last15 = Amdam | first15 = G. V. | last16 = Bitondi | first16 = M. M. G. | last17 = Collins | first17 = A. M. | last18 = Cristino | first18 = A. S. | last19 = Michael | first19 = H.| display-authors = 18 | pmc=2048586|bibcode = 2006Natur.443..931T }}</ref> 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.<ref>{{Cite journal | doi = 10.1126/science.1135213 | pmid = 17068262 | title = Functional CpG methylation system in a social insect | journal = Science | volume = 314 | issue = 5799| pages = 645–647 | year = 2006| last1 = Wang | first1 = Y. | last2 = Jorda | first2 = M. | last3 = Jones | first3 = P. L. | last4 = Maleszka | first4 = R. | last5 = Ling | first5 = X. | last6 = Robertson | first6 = H. M. | last7 = Mizzen | first7 = C. A. | last8 = Peinado | first8 = M. A. | last9 = Robinson | first9 = G. E. | bibcode = 2006Sci...314..645W| s2cid = 31709665 }}</ref>

===African variants===
There are two lineages of the East African lowland subspecies (''[[Apis mellifera scutellata]]'') in the Americas: actual matrilineal descendants of the original escaped queens and a much smaller number that are Africanized through hybridization. The matrilineal descendants carry African mtDNA, but partially European nuclear DNA, while the honey bees that are Africanized through hybridization carry European mtDNA, and partially African nuclear DNA. The matrilineal 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]],<ref>{{Cite journal | doi = 10.1038/339213a0 | pmid = 2566123 | title = Neotropical Africanized honey bees have African mitochondrial DNA | journal = Nature | volume = 339 | issue = 6221 | pages = 213–5 | year = 1989 | last1 = Smith | first1 = D. R. | last2 = Taylor | first2 = O. R. | last3 = Brown | first3 = W. M. | bibcode = 1989Natur.339..213S| hdl = 2027.42/62690 | s2cid = 4321598 | url = https://deepblue.lib.umich.edu/bitstream/2027.42/62690/1/339213a0.pdf }}</ref> 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.<ref>{{cite web |url=http://edis.ifas.ufl.edu/MG113 |id=ENY-114/MG113 |title=African Honey Bee: What You Need to Know |website=Edis.ifas.ufl.edu |publisher=University of Florida |access-date=2011-01-05 |archive-date=2008-06-23 |archive-url=https://web.archive.org/web/20080623084759/http://edis.ifas.ufl.edu/MG113 |url-status=dead }}</ref> Population genetics analysis of Africanized honey bees in the United States, using a maternally inherited genetic marker, found 12&nbsp;distinct mitotypes, and the amount of genetic variation observed supports the idea that there have been multiple introductions of AHB into the United States.<ref>{{cite journal |author=Szalanski, A.L. |author2=Magnus, R. |year=2010 |title=Mitochondrial DNA characterization of Africanized honey bee (''Apis mellifera'' L.) populations from the USA |journal=Journal of Apicultural Research and Bee World |volume=49 |issue=2 |pages=177–185 |url=http://comp.uark.edu/~aszalan/szalanski_magnus_ahb_usa_jar_2010.pdf |doi=10.3896/IBRA.1.49.2.06 |bibcode=2010JApiR..49..177S |s2cid=35085058 |access-date=2011-03-09 |archive-url=https://web.archive.org/web/20110725082000/http://comp.uark.edu/~aszalan/szalanski_magnus_ahb_usa_jar_2010.pdf |archive-date=2011-07-25 |url-status=dead }}</ref>

A newer publication shows the genetic admixture of the Africanized honey bees in Brazil. The small number of honey bees with African ancestry that were introduced to Brazil in 1956, which dispersed and hybridized with existing managed populations of European origin and quickly spread across much of the Americas, is an example of a massive biological invasion as earlier told in this article. Here, they analysed whole-genome sequences of 32&nbsp;Africanized honey bees sampled from throughout Brazil to study the effect of this process on genome diversity. By comparison with ancestral populations from Europe and Africa, they infer that these samples had 84% African ancestry, with the remainder from western European populations. However, this proportion varied across the genome and they identified signals of positive selection in regions with high European ancestry proportions. These observations are largely driven by one large gene-rich 1.4&nbsp;Mbp segment on chromosome 11 where European haplotypes are present at a significantly elevated frequency and likely confer an adaptive advantage in the Africanized honey bee population.<ref>{{Cite journal |author1=Ronald M. Nelson |author2=Andreas Wallberg |author3=Zilá Luz Paulino Simões |author4=Daniel J. Lawson |author5=Matthew T. Webster |title=Genomewide analysis of admixture and adaptation in the Africanized honeybee |journal=Molecular Ecology |volume=26 |issue=14 |pages=3603–3617 |doi=10.1111/mec.14122 |pmid=28378497 |year=2017 |bibcode=2017MolEc..26.3603N |hdl=1983/9a0f0728-cf3f-4eb8-8375-620db9a19ca0 |s2cid=13542834 |url=https://research-information.bristol.ac.uk/en/publications/genomewide-analysis-of-admixture-and-adaptation-in-the-africanized-honeybee(9a0f0728-cf3f-4eb8-8375-620db9a19ca0).html |type=Submitted manuscript |hdl-access=free }}</ref>