Laboratory rearing of mosquitos (Anopheles arabiensis): impact on genetic variability and implications for Sterile Insect Technique (SIT) based mosquito control in northern Sudan

The population genetic makeup of the 13th generation of a laboratory colony of Anopheles arabiensis mosquitos at 11 microsatellite loci was compared to that of the field population from which the colony was founded. Major changes which include significant reductions in the total number of alleles, the numbers of rare and private alleles, and the fractions of heterozygote individuals at all the loci were observed. The pattern of change is consistent with the expected effect of the use of a small number of mosquitos when the colony was established. Random genetic drift during the 13 generations of laboratory propagation could have contributed but the size of the colony population in successive generations was large enough to minimize this. The colony samples were at Hardy-Weinberg equilibrium at all the autosomal loci; the field population showed significant homozygote excess in three of them, as did the two X-linked loci in both populations. We attribute the homozygote excess to null-alleles. The Sterile Insect Techniques (SIT) program of mosquito control that is underway in Northern Sudan uses sterilized males produced from the colony population we studied. We discuss the potential fitness consequences of the loss of genetic diversity in the colony population and recommend their systematic investigation because they have direct and significant impact on the ultimate success of the SIT program.