Enzyme variation at the aspartate aminotransferase locus in members of the Anopheles gambiae complex (Diptera: Culicidae).

The enzyme aspartate aminotransferase (AAT) currently is used to identify Anopheles quadriannulatus Theobald, the animal-biting, nonmalaria vector species of the Anopheles gambiae complex. Samples of An. quadriannulatus from South Africa and An. gambiae Giles s.str. from the island of Grand Comoros and the People's Republic of Congo have shown variation in electromorph frequencies that indicate that AAT has five alleles. The three slowest alleles are found in An. quadriannulatus and the three fastest in An. gambiae, An. arabiensis Patton and An. merus Dönitz. One of these is common to both An. quadriannulatus and An. gambiae. This overlap indicates a potential misidentification of 0.3% of unknown females with a further 2.1% being unidentifiable. However, all of the specimens in the overlap area were classified correctly using octanol dehydrogenase (ODH). Variation at the ODH locus in An. quadriannulatus is recorded for the first time, with four of 157 specimens being heterozygous for the fast allele. The probability of both AAT and ODH giving an incorrect or indecisive identification is 0.0005. The slowest AAT alleles were present in samples from a single locality, indicating the lack of gene flow between subpopulations of An. quadriannulatus in close geographic proximity in the Shingwedzi area, South Africa. A modified method for multiple gel casting is given.