ESTIMATION OF GENETIC-DIVERGENCE AND GENE FLOW BETWEEN CULEX-PIPIENS AND CULEX-QUINQUEFASCIATUS (DIPTERA, CULICIDAE) IN ARGENTINA

Allele frequencies at seven polymorphic loci controlling the synthesis of enzymes were analyzed in six populations of Culex pipiens L. and C x. quinquefasciatus Say. Sampling sites were situated along a north-so uth line of about 2,000 km in Argentina. The predominant alleles at Md h, Idh, Gpdh and Gpi loci presented similar frequencies in all the sam ples. Frequencies at the Pgm locus were similar for populations pairs sharing the same geographic area. The loci Cat and Hk-1 presented sign ificant geographic variation. The latter showed a marked latitudinal d ine, with a frequency for allele b ranging from 0.99 in the northernmo st point to 0.04 in the southernmost one, a pattern that may be explai ned by natural selection (F-ST 0.46; p < 0.0001) on heat sensitive all eles. The average value of F-ST(0.088) and Nm (61.12) indicated a high gene flow between adjacent populations. A high col relation was found between genetic and geographic distance (r = 0.83; p < 0.001). The hi ghest genetic identity (I-N = 0.988) corresponded to the geographicall y closest samples from the central area. In one of these localities Cx . quinquefasciatus was predominant and hybrid individuals were detecte d, while in the other, almost all the specimens were identified as Cx. pipiens. To verify the fertility between Cx. pipiens and Cx. quinquef asciatus from the northern-and southernmost populations, experimental crosses were performed. Viable egg rafts were obtained from both recip rocal crosses. Hatching ranged from 76.5 to 100%. The hybrid progenies were fertile through two subsequent generations.