Allozyme variation, population structure, and sibling species in Aphis pomi

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Abstract
Apterous apple aphids (A. pomi de Geer) collected from several southern Ontario [Canada] orchards in several seasons were studied electrophoretically for 17 enzyme and 2 protein loci. Sixteen loci proved monomorphic. The remaining 3 showed a strong association among loci; all individuals that are homozygous for the fast allele of glutamate oxaloacetate transaminase (Got) also have no esterase1 activity (presumably being fixed for a null allele) and have a unique banding phenotype for esterase 2 (a locus for which no Mendelian model could be made). The remaining aphids are fixed for the slow Got allele, have 2 active alleles segregating at esterase 1 and showed either of 2 banding phenotypes at esterase 2. Apparently, A. pomi consists of 2 differentiated, noninterbreeding subpopulations. The 1st type increased from rarity to near fixation in southern Ontario since 1978, and may be spreading up the Niagara Peninsula. It has greater resistance to malathion than the replaced type.