Genetic characterization of U.S. honey bee populations

The history of honey bee importation into North America began in the 17th century. Between 1622 and 1859 eight subspecies were brought into North America. Small numbers of queens representing these subspecies were initially brought over and are the genetic ancestors of the populations that remain in the United States today. In 1987 Varroa destructor, a parasitic brood mite, was found in the United States. It has been responsible for the near elimination of the once flourishing feral honey bee population, and has annually reduced the commercial honey bee populations. The reduction of honey bee numbers by Varroa caused a second genetic bottleneck of the U.S. populations. A third genetic bottleneck can be attributed to current queen breeding practices. Queen breeders typically use a small number of breeder queens to make a large number of replacement queens for managed colonies. My data shows that 473 breeder queens were used to make replacement queens for 1/3 of all managed colonies in the United States.These three population bottleneck events underlie our concerns for the genetic diversity of the honey bee in the United States. To better understand changes in the genetic diversity of honey bee populations, feral populations collected between 1980 and 1992 and commercial populations from the southeastern and western United States collected in 1993-1994 and again in 2004-2005 were analyzed using mitochondrial and microsatellite DNA.The results indicate that feral populations collected between 1980 and 1992 were genetically different from the managed populations, and the feral populations probably served as a source of allelic diversity for both the managed populations. The genetic composition of the two managed populations was different. The western managed population experienced a significant loss of original alleles over the ten year sample period, likely due to genetic drift and or bottlenecks caused by Varroa destructor and breeding practices. However, there was also a simultaneous gain of "new" alleles into both the western and southeastern managed populations probably reflecting contributions from additional introductions of Russian or Carniolan strains or from Africanized honey bees.