Hidden Sylvatic Foci of the Main Vector of Chagas Disease Triatoma infestans: Threats to the Vector Elimination Campaign?

Triatoma infestans, a highly domesticated species and historically the main vector of Trypanosoma cruzi, is the target of an insecticide-based elimination program in the southern cone countries of South America since 1991. Only limited success has been achieved in the Gran Chaco region due to repeated reinfestations. We conducted full-coverage spraying of pyrethroid insecticides of all houses in a well-defined rural area in northwestern Argentina, followed by intense monitoring of house reinfestation and searches for triatomine bugs in sylvatic habitats during the next two years, to establish the putative sources of new bug colonies. We found low-density sylvatic foci of T. infestans in trees located within the species' flight range from the nearest infested house detected before control interventions. Using multiple methods (fine-resolution satellite imagery, geographic information systems, spatial statistics, genetic markers and wing geometric morphometry), we corroborated the species identity of the sylvatic bugs as T. infestans and found they were indistinguishable from or closely related to local domestic or peridomestic bug populations. Two sylvatic foci were spatially associated to the nearest peridomestic bug populations found before interventions. Sylvatic habitats harbor hidden foci of T. infestans that may represent a threat to vector suppression attempts

Molecular population genetics and phylogeography of the Chagas disease vector Triatoma infestans in South America

Knowledge of the genetic variability, population structure, and evolutionary history of Triatoma infestans may be useful for developing rational vector control strategies. A 661-bp fragment of the mitochondrial gene cytochrome oxidase 1 (COI) was sequenced and analyzed in bugs from Argentina, Uruguay, Peru, and Bolivia, including peridomestic, domestic, Andean, and Chaco sylvatic bugs. A total of 48 polymorphic sites among 37 haplotypes were described. Nucleotide variation fluctuated among samples, with the highest nucleotide diversity observed in seven Argentinean provinces. Within this group, some populations showed patterns of variability compatible with population expansions and/or fine-scale population structure, whereas others suggested population bottlenecks and/or population admixture processes. A maximum parsimony analysis of the haplotypes showed the presence of a Bolivian/Peruvian and an Argentinean/Uruguayan clade. Bolivian sequences were further divided in Chaco sylvatic and Andean domestic and sylvatic. Two different nested clades were found within the Argentinean/Uruguayan cluster. Analysis of molecular variance (AMOVA) and K-S(T)* analysis supported a strong population structure in Argentina, where genetic differentiation was correlated with geographic distance. Departures from neutrality expectations and a nested cladistic analysis suggest a recent population expansion of T. infestans in Argentina, followed by restricted gene flow and patterns of isolation by distance. This expansion could have taken place as a two-wave process, as was shown by the phylogenetic analysis and signatures of population admixture in the southernmost Argentinean populations

Molecular Population Genetics of the α-Esterase5 Gene Locus in Original and Colonized Populations of 'Drosophila buzzatii' and Its Sibling 'Drosophila koepferae'

Several studies have suggested that esterase-2 (EST-2) may be the target of natural selection in the cactophilic fly 'Drosophila buzzatii'. In this work, we analyzed nucleotide variation in a fragment of α-esterase5 (αE5), the gene encoding EST-2, in original (Argentinian) and colonized (Australian) populations of 'D. buzzatii' and in its sibling 'D. koepferae'. Estimates of nucleotide heterozygosity in 'D. buzzatii' were similar in Australia and Argentina, although we detected a loss of singletons in colonized populations, suggesting a moderate founder effect. Interspecific comparisons revealed that 'D. buzzatii' was more polymorphic for nonsynonymous variation, whereas 'D. koepferae' was more variable for synonymous and noncoding sites. The two major chromosomal arrangements (2st and 2j) in 'D. buzzatii' displayed similar levels of nucleotide variation, whereas 2jz3 was monomorphic. The sequenced region allowed the discrimination of a greater number of EST-2 protein variants in the Australian sample than in the Argentinean sample. In 'D. koepferae', nucleotide variation in αE5 does not depart from neutral expectations, although tests of population structure were significant for silent variation. In contrast, 'D. buzzatii' has probably undergone a recent population expansion in its South American range. In addition, the McDonald and Kreitman test revealed an excess of nonsynonymous polymorphism in both original and colonized populations of this species

Sylvatic Triatoma infestans (Reduviidae, Triatominae) in the Andean valleys of Bolivia

Triatoma infestans is the main vector of Chagas disease in the Southern Cone countries. Wild populations of T. infestans appear widespread throughout the Andean valleys of Bolivia. In Cotapachi (2750 m asl), all sorts of rocky outcrops, regardless of their size. provided good refuges for T. infestans. Of the 1120 ecotopes investigated, 330 (29.5%) contained triatomines and 92% of the collected insects were nymphal instars. In the cold season, triatomine densities were similar in small and large outcrops. During the hot season. bug densities were higher in the larger outcrops, particularly in those located in peridomestic sites. T. infestans populations apparently produced one generation per year. Over half the sampled bugs were positive for T. cruzi infection. At Mataral (1750 m asl), a site located in the inter-Andean Chaco, a new morph of T. infestans was detected in a sylvatic environment