Africanized Bee - Morphology and Genetics

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 be reliably recognized only by performing a statistical analysis on micro-measurements of a substantial sample. One problem with this test is that there are also others subspecies, the first Americas naturalized Apis mellifera iberiensis with shorter wings too, is having from ancient hybridated haplotypes that presents six different lineages, five of them correspond to evolutionary lineages from Africa. Some belong to Apis mellifera intermissa but others are having 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 analysed 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 West Europa. 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.