<P> A. mellifera phylogeny is the most enigmatic of all honey bee species . It seems to have diverged from its eastern relatives only during the Late Miocene . This would fit the hypothesis that the ancestral stock of cave - nesting honey bees was separated into the western group of East Africa and the eastern group of tropical Asia by desertification in the Middle East and adjacent regions, which caused declines of food plants and trees that provided nest sites, eventually causing gene flow to cease . </P> <P> The diversity of A. mellifera subspecies is probably the product of a largely Early Pleistocene radiation aided by climate and habitat changes during the last ice age . That the western honey bee has been intensively managed by humans for many millennia--including hybridization and introductions--has apparently increased the speed of its evolution and confounded the DNA sequence data to a point where little of substance can be said about the exact relationships of many A. mellifera subspecies . </P> <P> Apis mellifera is not native to the Americas, so was not present upon the arrival of the European explorers and colonists . However, other native bee species were kept and traded by indigenous peoples . In 1622, European colonists brought the dark bee (A. m. mellifera) to the Americas, followed later by Italian bees (A. m. ligustica) and others . Many of the crops that depend on honey bees for pollination have also been imported since colonial times . Escaped swarms (known as "wild" bees, but actually feral) spread rapidly as far as the Great Plains, usually preceding the colonists . Honey bees did not naturally cross the Rocky Mountains; they were transported by the Mormon pioneers to Utah in the late 1840s, and by ship to California in the early 1850s . </P> <P> Africanized bees (known colloquially as "killer bees") are hybrids between European stock and one of the African subspecies A. m. scutellata; they are often more aggressive than European bees and do not create as much of a honey surplus, but are more resistant to disease and are better foragers . Originating by accident in Brazil, they have spread to North America and constitute a pest in some regions . However, these strains do not overwinter well, so are not often found in the colder, more northern parts of North America . The original breeding experiment for which the African bees were brought to Brazil in the first place has continued (though not as intended). Novel hybrid strains of domestic and redomesticated Africanized bees combine high resilience to tropical conditions and good yields . They are popular among beekeepers in Brazil . </P>

When were honey bees brought to north america