The genetic structure in populations of the Chagas' disease vector Triatoma infestans was examined. Comparisons of the levels of genetic variability in populations of this species from areas with different periods since last insecticide treatment and from areas that never received treatment were also carried out. A total of 598 insects from 19 populations were typed for 10 polymorphic microsatellite loci. The average observed and expected heterozygosities ranged from 0.186 to 0.625 and from 0.173 to 0.787, respectively. Genetic drift and limited gene flow appear to have generated a substantial degree of genetic differentiation among the populations of T. infestans. Departures from Hardy-Weinberg expectations due to an excess of homozygotes suggested the presence of null alleles and population subdivision. Microgeographical analysis supports the existence of subdivision in T. infestans populations. Levels of genetic diversity in the majority of the populations of T. infestans from insecticide-treated localities were similar or higher than those detected in populations from areas without treatment. Since the populations of T. infestans are subdivided, a population bottleneck would result in independent genetic drift effects that could randomly preserve different combinations of alleles in each subpopulation. These events followed by a rapid population growth could have preserved high levels of genetic diversity. This study supports the hypothesis of vector population recovery from survivors of the insecticide-treated areas and therefore highlights the value of population genetic analyses in assessing the effectiveness of Chagas' disease vector control programmes.

The subfamily Triatominae (Hemiptera: Reduviidae) comprises hematophagous insects, most of which are actual or potential vectors of Trypanosoma cruzi, the protozoan agent of Chagas' disease (American trypanosomiasis). DNA sequence comparisons of mitochondrial DNA (mtDNA) genes were used to infer phylogenetic relationships among 32 species of the subfamily Triatominae, 26 belonging to the genus Triatoma and six species of different genera. We analyzed mtDNA fragments of the 12S and 16S ribosomal RNA genes (totaling 848-851 bp) from each of the 32 species, as well as of the cytochrome oxidase I (COI, 1447 bp) gene from nine. The phylogenetic analyses unambiguously supported several clusters within the genus Triatoma. In the morphological classification, T. costalimai was placed tentatively within the infestans complex while T. guazu was not included in any Triatoma complex. The placement of these species in the molecular phylogeny indicated that both belong to the infestans complex. We confirmed with a strong support the inclusion of T. circummaculata, a member of a different complex based on morphology, within the infestans complex. On the other hand, the present phylogenetics analysis did not support the monophyly of the infestans complex species as it was suggested in our previous studies. While no strong inference of polyphyly of the genus Triatoma was provided by the bootstrap analyses, the other species belonging to Triatomini analyzed could not be distinguished from the species of Triatoma.

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