Genetic variability and geographic differentiation among three species of Triatomine bugs (Hemiptera-Reduviidae)

Chemotaxonomy of Five South American Species of the Triatoma genus (Hemiptera: Reduviidae: Triatominae) Based on Their Cuticle Hydrocarbon Pattern

The Triatoma sordida subcomplex traditionally included four triatomine species, T. sordida, Triatoma garciabesi, Triatoma guasayana, and Triatoma patagonica, distributed in the Southern Cone of South America. These species have a large intraspecific variability together with an overall similarity, making difficult to establish their taxonomic status. Many cytogenetic, morphometric, and molecular markers have been applied to address this. Recent studies have posed concerns on the inclusion of T. guasayana and T. patagonica within the subcomplex. Also, T. sordida from Argentina has been designed as a new species, Triatoma rosai. Using the cuticular hydrocarbon pattern as chemotaxonomic marker, the relationships among several populations of these species were analyzed by capillary gas chromatography and linear discriminant analysis along 25 collection sites in Argentina, Bolivia, Brazil, and Paraguay. T. sordida and T. rosai populations were differentially clustered in two CHC-based groups: "Group 1" included T. sordida from Eastern Brazil, Eastern Paraguay, and the Bolivian populations from La Paz and Izozog G1; "Group 2" included T. rosai, and T. sordida from Izozog G2 (Bolivia), and Western Paraguay. Whereas T. garciabesi remained closely related to T. sordida and T. rosai, T. guasayana, and T. patagonica were clearly separated from the species of the T. sordida subcomplex. Our results agree with those from other several techniques suggesting that the taxonomy of the T. sordida subcomplex should be revised.

Trends in Taxonomy of Chagas Disease Vectors (Hemiptera, Reduviidae, Triatominae): From Linnaean to Integrative Taxonomy

Chagas disease is a neglected tropical disease caused by the protozoan Trypanosoma cruzi and transmitted mainly by members of the subfamily Triatominae. There are currently 157 species, grouped into 18 genera and five tribes. Most descriptions of triatomine species are based on classical taxonomy. Facing evolutionary (cryptic speciation and phenotypic plasticity) and taxonomic (more than 190 synonymizations) problems, it is evident that integrative taxonomy studies are an important and necessary trend for this group of vectors. Almost two-and-a-half centuries after the description of the first species, we present for the first time the state-of-the-art taxonomy of the whole subfamily, covering from the initial classic studies to the use of integrative taxonomy.

Phylogenetic and phenotypic relationships of the Triatoma sordida subcomplex (Hemiptera: Reduviidae: Triatominae)

Chagas disease, whose etiological agent is the protozoan Trypanosoma cruzi, affects millions of people worldwide and it is mainly transmitted by infected triatomine feces. Triatoma is the most diverse genus and one of the most important from an epidemiological point of view. Species of this genus are grouped into eight complexes and nine subcomplexes. Triatoma sordida subcomplex consists of T. garciabesi, T. guasayana, T. patagonica, and, T. sordida. Given the recent discussions on their phylogenetic status, this study aims to evaluate morphometric and genetics characters that group and distinguish T. garciabesi, T. guasayana, T. patagonica, and T. sordida, as well as to infer the phylogenetic relationships within the group and evaluate the proximity with T. rubrovaria subcomplex. The results corroborate the phylogenetic relationship of T. guasayana and T. patagonica with the T. rubrovaria subcomplex. Molecular data confirm the proximity of T. jurbergi, T. matogrossensis, T. vandae as T. garciabesi, and T. sordida. Together, genetic variability was shown between T. sordida populations.

Triatoma rosai sp. nov. (Hemiptera, Triatominae): A New Species of Argentinian Chagas Disease Vector Described Based on Integrative Taxonomy

Simple Summary

Although all triatomines are potential vectors of Chagas' disease, there are species with greater or lesser vectorial importance. Therefore, the correct identification of triatomines species is essential for the vector control programs. In general, triatomines are identified by external morphological characters. However, some species are very similar or even morphologically identical, being important the use of complementary analyses for the correct identification of species. For this reason, this study focused on the use of morphological, morphometric, molecular data, and experimental crosses to describe Triatoma rosai sp. nov., a new species of Argentinian Chagas disease vector. Significant morphological and morphometric differences, associated with phylogenetic support and high mortality rate of the hybrids made it possible to confirm the specific status of T. rosai sp. nov., emphasizing the importance of integrative analyses for the taxonomy of triatomines.

Abstract

Chagas disease is the most prevalent neglected tropical disease in the Americas and makes an important contribution to morbidity and mortality rates in countries where it is endemic since 30 to 40% of patients develop cardiac diseases, gastrointestinal disorders, or both. In this paper, a new species of the genus Triatoma is described based on specimens collected in the Department San Miguel, Province of Corrientes, Argentina. Triatoma rosai sp. nov. is closely related to T. sordida (Stål, 1859), and was characterized based on integrative taxonomy using morphological, morphometric, molecular data, and experimental crosses. These analyses, combined with data from the literature (cytogenetics, electrophoresis pattern, molecular analyses, cuticular hydrocarbons pattern, geometric morphometry, cycle, and average time of life as well as geographic distribution) confirm the specific status of T. rosai sp. nov. Natural Trypanosoma cruzi infection, coupled with its presence mostly in peridomestic habitats, indicates that this species can be considered as an important Chagas disease vector from Argentina.

Identifying Chagas disease vectors using elliptic Fourier descriptors of body contour: a case for the cryptic dimidiata complex

BACKGROUND

Triatoma dimidiata (Reduviidae: Triatominae) is an important vector of Chagas disease in various countries in the Americas. Phylogenetic studies have defined three lineages in Mexico and part of Central America. While there is a marked genetic differentiation, methods for identifying them using morphometric analyses with landmarks have not yet been fully resolutive. Elliptical Fourier descriptors (EFDs), which mathematically describe the shape of any closed two-dimensional contours, could be a potentially useful alternative method. Our objective was to validate the use of EFDs for the identification of three lineages of this species complex.

METHOD

A total of 84 dorsal view images of individuals of the three lineages were used. Body contours were described with EFDs using between 5 and 30 harmonics. The number of obtained coefficients was reduced by a principal components analysis and the first axis scores were used as shape variables. A linear discriminant function analysis and an ordination plot of the discriminant analysis were performed using the shape variables. A confusion matrix of the ordination plot of the discriminant analysis was obtained to estimate the classification errors, the first five PC scores were statistically compared, and a neural network were then performed using the shape variables.

RESULTS

The first principal component explained 50% of the variability, regardless the number of harmonics used. The results of discriminant analysis get improved by increasing the number of harmonics and components considered. With 25 harmonics and 30 components, the identification of haplogroups was achieved with an overall efficiency greater than 97%. The ordering diagram showed the correct discrimination of haplogroups, with only one error of discrimination corroborated by the confusion matrix. When comparing the first five PC scores, significant differences were found among at least two haplogroups. The 30 multilayer perceptron neural networks were also efficient in identification, reaching 91% efficiency with the validation data.

CONCLUSIONS

The use of EFD is a simple and useful method for the identification of the main lineages of Triatoma dimidiata, with high values of correct identification.

CytoKey: Identification Key for the Chagas Disease Vectors of the Largest Brazilian Urban Center (São Paulo State), Based on Cytogenetic Data

Chagas disease is caused by the protozoan Trypanosoma cruzi. This disease is distributed in 21 Latin American countries, where it is mostly vector-borne. In Brazil, there are 68 triatomine species. To date, the epidemiological surveys indicate that the state of São Paulo presents 11 species of triatomines, and most of these species have already been collected in a home environment and found to be infected with T. cruzi. Problems in correctly identifying species can lead to incorrect panorama of distribution of Chagas disease vectors. Thus, we developed an identification key for the triatomines of the state of São Paulo, based on cytogenetic data. With the exception of Panstrongylus diasi that does not present cytogenetic data available in the literature, all species were differentiated by cytogenetic characteristics. We emphasize the importance of using this key as a simple and objective tool in the entoepidemiological surveys conducted by the vector control programs.

Genetic Structure of Brazilian Populations of Triatoma sordida (Stål, 1859) (Hemiptera, Triatominae) by Means of Chromosomal Markers

Triatoma sordida is among the main Brazilian species considered as Chagas disease vectors. The genetic studies are directed mainly to phylogenetic questions because this species possibly have suffered cryptic speciation. Furthermore, there are few studies that analyzed the structure and genetic variability of specimens from Brazil and that showed low genetic diversity and strong genetic structuring of the population samples. Therefore, because of great epidemiological importance of T. sordida and mainly the restriction of genetic characterization of this vector only for populations of Minas Gerais state, this article performs a genetic analysis of the T. sordida from seven different Brazilian states (representing different biomes), by means of cytogenetic markers. All analyzed specimens presents the same cytogenetic characteristics: early meiotic prophase with several heterochromatic bodies dispersed in the nucleus (CG-rich), being one of them formed by the associated sex chromosomes surrounded by some autosomal heterochromatic regions, meiotic metaphase with most autosomal pairs exhibiting a C-heterochromatic block in one chromosomal end (CG-rich), Y sex chromosome fully heterochromatin (AT-rich), and X chromosome may present a small C-block (CG-rich). These results are important because the chromosomal markers enable to confirm and expand the low genetic diversity for all Brazilian states occupied by T. sordida, suggesting that all Brazilian populations were originated from a small ancestral population and possibly dispersed to other biomes by founder effect. In addition, we suggest that T. sordida from Brazil are not suffering cryptic speciation and we confirm the classification of all Brazilian examples as T. sordida sensu stricto.

Evolution, Systematics, and Biogeography of the Triatominae, Vectors of Chagas Disease

In this chapter, we review and update current knowledge about the evolution, systematics, and biogeography of the Triatominae (Hemiptera: Reduviidae)-true bugs that feed primarily on vertebrate blood. In the Americas, triatomines are the vectors of Trypanosoma cruzi, the etiological agent of Chagas disease. Despite declining incidence and prevalence, Chagas disease is still a major public health concern in Latin America. Triatomines occur also in the Old World, where vector-borne T. cruzi transmission has not been recorded. Triatomines evolved from predatory reduviid bugs, most likely in the New World, and diversified extensively across the Americas (including the Caribbean) and in parts of Asia and Oceania. Here, we first discuss our current understanding of how, how many times, and when the blood-feeding habit might have evolved among the Reduviidae. Then we present a summary of recent advances in the systematics of this diverse group of insects, with an emphasis on the contribution of molecular tools to the clarification of taxonomic controversies. Finally, and in the light of both up-to-date phylogenetic hypotheses and a thorough review of distribution records, we propose a global synthesis of the biogeography of the Triatominae. Over 130 triatomine species contribute to maintaining T. cruzi transmission among mammals (sometimes including humans) in almost every terrestrial ecoregion of the Americas. This means that Chagas disease will never be eradicated and underscores the fact that effective disease prevention will perforce require stronger, long-term vector control-surveillance systems.

Taxonomical over splitting in the Rhodnius prolixus (Insecta: Hemiptera: Reduviidae) clade: Are R. taquarussuensis (da Rosa et al., 2017) and R. neglectus (Lent, 1954) the same species?

The use of subtle features as species diagnostic traits in taxa with high morphological similarity sometimes fails in discriminating intraspecific variation from interspecific differences, leading to an incorrect species delimitation. A clear assessment of species boundaries is particularly relevant in disease vector organisms in order to understand epidemiological and evolutionary processes that affect transmission capacity. Here, we assess the validity of the recently described Rhodnius taquarussuensis (da Rosa et al., 2017) using interspecific crosses and molecular markers. We did not detect differences in hatching rates in interspecific crosses between R. taquarussuensis and R. neglectus (Lent, 1954). Furthermore, genetic divergence and species delimitation analyses show that R. taquarussuensis is not an independent lineage in the R. prolixus group. These results suggest that R. taquarussuensis is a phenotypic form of R. neglectus instead of a distinct species. We would like to stress that different sources of evidence are needed to correctly delimit species. We consider this is an important step in understanding vectorial Chagas disease spread and transmission.

Morphometric variability among the species of the Sordida subcomplex (Hemiptera: Reduviidae: Triatominae): evidence for differentiation across the distribution range of Triatoma sordida

BACKGROUND

The Sordida subcomplex (Triatominae) comprises four species, Triatoma garciabesi, T. guasayana, T. patagonica and T. sordida, which differ in epidemiological importance and adaptations to human environments. Some morphological similarities among species make taxonomic identification, population differentiation and species delimitation controversial. Triatoma garciabesi and T. sordida are the most similar species, having been considered alternatively two and a single species until T. garciabesi was re-validated, mostly based on the morphology of male genitalia. More recently, T. sordida from Argentina has been proposed as a new cryptic species distinguishable from T. sordida from Brazil, Bolivia and Paraguay by cytogenetics. We studied linear and geometric morphometry of the head, wings and pronotum in populations of these species aiming to find phenotypic markers for their discrimination, especially between T. sordida and T. garciabesi, and if any set of variables that validates T. sordida from Argentina as a new species.

RESULTS

Head width and pronotum length were the linear variables that best differentiated species. Geometric morphometry revealed significant Mahalanobis distances in wing shape between all pairwise comparisons. Triatoma patagonica exhibited the best discrimination and T. garciabesi overlapped the distribution of the other species in the morphometric space of the first two DFA axes. Head shape showed differentiation between all pairs of species except for T. garciabesi and T. sordida. Pronotum shape did not differentiate T. garciabesi from T. guasayana. The comparison between T. garciabesi and T. sordida from Argentina and T. sordida from Brazil and Bolivia revealed low differentiation based on head and pronotum linear measurements. Pronotum and wing shape were different between T. garciabesi and T. sordida from Brazil and Bolivia and T. sordida from Argentina. Head shape did not differentiate T. garciabesi from T. sordida from Argentina.

CONCLUSIONS

Wing shape best delimited the four species phenotypically. The proposed cryptic species, T. sordida from Argentina, differed from T. sordida from Brazil and Bolivia in all measured shape traits, suggesting that the putative new species may not be cryptic. Additional studies integrating cytogenetic, phenotypic and molecular markers, as well as cross-breeding experiments are needed to confirm if these three entities represent true biological species.

A new species of Rhodnius from Brazil (Hemiptera, Reduviidae, Triatominae)

A colony was formed from eggs of a Rhodnius sp. female collected in Taquarussu, Mato Grosso do Sul, Brazil, and its specimens were used to describe R.taquarussuensissp. n. This species is similar to R.neglectus, but distinct characters were observed on the head, thorax, abdomen, female external genitalia and male genitalia. Chromosomal differences between the two species were also established.

Morphological and Genetic Differentiation within the Southernmost Vector of Chagas Disease: Triatoma patagonica (Hemiptera - Reduviidae)

The epidemiological importance of Chagas disease vectors largely depends on their spreading ability and adaptation to domestic habitats. Triatoma patagonica is a secondary vector of Chagas disease endemic of Argentina, and it has been found colonizing domiciles and most commonly peridomiciliary structures in several Argentine provinces and morphological variation along its distribution range have been described. To asses if population differentiation represents geographic variants or true biological species, multiple genetic and phenotypic approaches and laboratory cross-breeding were performed in T. patagonica peridomestic populations. Analyses of chromatic variation of forewings, their size and the content of C-heterochromatin on chromosomes revealed that populations are structured following a North-South latitudinal variation. Cytochrome c oxidase I mitochondrial gene (COI) nucleotide analysis showed a mean genetic distance of 5.2% between the most distant populations. The cross-breeding experiments suggest a partial reproductive isolation between some populations with 40% of couples not laying eggs and low hatching efficiency. Our findings reveal phenotypic and genetic variations that suggest an incipient differentiation processes among T. patagonica populations with a pronounced phenotypic and genetic divergence between the most distant populations. The population differentiation here reported is probably related to differential environmental conditions and it could reflect the occurrence of an incipient speciation process in T. patagonica.

New arrangements on several species subcomplexes of Triatoma genus based on the chromosomal position of ribosomal genes (Hemiptera - Triatominae)

The hemipteran subfamily Triatominae includes 150 blood-sucking species, vectors of Chagas disease. By far the most specious genus is Triatoma, assembled in groups, complexes and subcomplexes based on morphological similarities, geographic distribution and genetic data. However, many molecular studies questioned the species integration of several subcomplexes as monophyletic units. In triatomines, chromosomal position of major ribosomal DNA (rDNA) loci is extremely variable but seems to be species-specific and an evolutionary conserved genetic trait, so that closely related species tend to have ribosomal clusters in the same chromosomal location. Considering that the autosomal position as the ancestral character for all heteropteran species, including triatomines, we suggest that the movement of rDNA loci from autosomes to sex chromosomes rapidly established reproductive barriers between divergent lineages. We proposed that the rDNA translocation from the autosomes to the sex chromosomes restrict reproductive compatibility and eventually promote speciation processes. We analyzed the chromosomal position of 45S rDNA clusters in almost all species of the matogrossensis, rubrovaria, maculata and sordida subcomplexes. The fluorescent in situ hybridization results are discussed considering the available genetic data and we proposed new arrangements in the species that constitute each one of these subcomplexes.

New sex-determination system in the genus Panstrongylus (Hemiptera: Reduviidae) revealed by chromosomal analysis of Panstrongylus lutzi

BACKGROUND

Panstrongylus lutzi (Neiva & Pinto, 1923) is a triatomine species native to Caatinga habitats in north-eastern Brazil. It is considered an important vector of Chagas disease in this region, presenting high rates of natural infection with Trypanosoma cruzi Chagas, 1909, and readily invading houses by flight. This study describes a previously unknown chromosomal sex system in the genus Panstrongylus based on P. lutzi.

METHODS

Fifth-instar and male adults of P. lutzi originating from municipality of Várzea Alegre, Ceará (Brazil) were analysed. Chromosomal analyses of male meiotic process were done by Giemsa staining.

RESULTS

Chromosomal analyses of male meiosis reveal a diploid chromosome number of 24 chromosomes (20 autosomes plus X1X2X3Y). During meiotic prophase I, the sex chromosomes remained close together, forming four heteropycnotic chromocenters in zygotene, and a single chromocenter in pachytene and diplotene. Still at the diplotene stage, each one of the ten autosomal bivalents showed an evident chiasma. In metaphase I, the four sex chromosomes appeared clearly separated. The three X chromosomes were the smallest of the complement and isopycnotic with respect to the Y chromosome. Two bivalents appear larger, whereas the other eight showed no significant difference in size.

CONCLUSION

Karyotype analysis of P. lutzi revealed a new sex system in the genus Panstrongylus. This result is of utmost importance to karyosystematics of P. lutzi, and demonstrates the need for further studies of this type in the subfamily Triatominae.

Assessing the mitochondrial DNA diversity of the Chagas disease vector Triatoma sordida (Hemiptera: Reduviidae)

Triatoma sordida is a species that transmits Trypanosoma cruzi to humans. In Brazil, T. sordida currently deserves special attention because of its wide distribution, tendency to invade domestic environments and vectorial competence. For the planning and execution of control protocols to be effective against Triatominae, they must consider its population structure. In this context, this study aimed to characterise the genetic variability of T. sordida populations collected in areas with persistent infestations from Minas Gerais, Brazil. Levels of genetic variation and population structure were determined in peridomestic T. sordida by sequencing a polymorphic region of the mitochondrial cytochrome b gene. Low nucleotide and haplotype diversity were observed for all 14 sampled areas; π values ranged from 0.002-0.006. Most obtained haplotypes occurred at low frequencies, and some were exclusive to only one of the studied populations. Interpopulation genetic diversity analysis revealed strong genetic structuring. Furthermore, the genetic variability of Brazilian populations is small compared to that of Argentinean and Bolivian specimens. The possible factors related to the reduced genetic variability and strong genetic structuring obtained for studied populations are discussed in this paper.

Cryptic speciation in the Triatoma sordida subcomplex (Hemiptera, Reduviidae) revealed by chromosomal markers

BACKGROUND

Chagas disease vectors (Hemiptera-Reduviidae) comprise more than 140 blood-sucking insect species of the Triatominae subfamily. The largest genus is Triatoma, subdivided in several complexes and subcomplexes according to morphology, ecology and genetic features. One of them is the sordida subcomplex, involving four species: Triatoma sordida, T. guasayana, T. garciabesi and T. patagonica. Given the great morphological similarity of these species, their taxonomic identification, evolutionary relationships and population differentiation have been controversial for many years and even today remain under discussion.

METHODS

We simultaneously analyzed two chromosomal markers, C-heterochromatin distribution and 45S ribosomal genes chromosomal position, of 139 specimens from several sordida subcomplex populations from Argentina, Bolivia, Brazil and Paraguay, collected both in nature and from several established insectaries. Our results were compared with COI sequences deposited in GenBank.

RESULTS

We recognized five chromosomal taxa with putative hybrids, which each differ in at least one chromosome marker. Most of them present significant differences in their mtDNA sequences.

CONCLUSION

The chromosomal taxa here show a significant chromosome differentiation involving changes in the C-heterochromatin content and in the ribosomal clusters position. This paper identifies several erroneously classified populations by morphological methods, delimits the geographical distribution of each taxon and proposes the existence of a new cryptic species, widely distributed in Argentina. We also suggest that sordida sibling species involve closely related as well as evolutionary distant species. Taxonomic status of each chromosomal taxon is discussed considering phenotypic and genetic results previously published.

Chromosomal characteristics and distribution of constitutive heterochromatin in the Matogrossensis and Rubrovaria subcomplexes

Since 1966 the triatomines were grouped in complexes and specific subcomplexes. Although the complex and subcomplexes not have taxonomic importance, should be monophyletic groups and cytogenetic tools have proved to be of great importance to characterize these species groupings. Based on this, this paper aims to describe the chromosomal characteristics and heterochromatic pattern of Matogrossensis and Rubrovaria subcomplexes, in order to contribute to the taxonomic and evolutionary relationships of these vectors. In this study, at least three males from each species (Triatoma baratai, Triatoma costalimai, Triatoma guazu, Triatoma jurbergi, Triatoma matogrossensis, Triatoma vandae, Triatoma williami, Triatoma carcavalloi, Triatoma circummaculata, Triatoma klugi, Triatoma pintodiasi and Triatoma rubrovaria) were analyzed by means analyzed by means of cytogenetic techniques of C-banding. All species showed the same cytogenetic characteristics: 22 chromosomes, low variation in the size of autosomes, sex chromosome Y larger than X, initial prophase composed of only one heterochromatic chromocenter formed by the sex chromosomes X and Y (except for T. pintodiasi that presented the sex chromosomes individualized during all stages of prophase) and presence of constitutive heterochromatin restricted to sex chromosome Y. These characteristics, although common to Matogrossensis and Rubrovaria subcomplexes allow to distinguish these species of species grouped in most of South America subcomplexes, as Brasiliensis, Maculata, Sordida and Insfestans. Thus, the cytogenetic analysis was of extreme importance to differentiate both subcomplexes of the other subcomplexes of South America. However, probably due to evolutionary proximity existing between these subcomplexes was not possible to observar species differences that make up the Matogrossensis subcomplex of the Rubrovaria subcomplex. Therefore, we emphasize that new comparative analyzes, as experimental hybrid crosses and molecular cytogenetic analysis are necessary to clarify the evolutionary relationship between these important subcomplexes of vectors.

The cuticular hydrocarbons of the Triatoma sordida species subcomplex (Hemiptera: Reduviidae)

The cuticular hydrocarbons of the Triatoma sordida subcomplex (Hemiptera: Reduviidae: Triatominae) were ana-lysed by gas chromatography and their structures identified by mass spectrometry. They comprised mostly n-alkanes and methyl-branched alkanes with one-four methyl substitutions. n-alkanes consisted of a homologous series from C21-C33 and represented 33-45% of the hydrocarbon fraction; n-C29 was the major component. Methyl-branched alkanes showed alkyl chains from C24-C43. High molecular weight dimethyl and trimethylalkanes (from C35-C39) represented most of the methyl-branched fraction. A few tetramethylalkanes were also detected, comprising mostly even-numbered chains. Several components such as odd-numbered 3-methylalkanes, dimethylalkanes and trimethylalkanes of C37 and C39 showed patterns of variation that allowed the differentiation of the species and populations studied. Triatoma guasayana and Triatoma patagonica showed the most distinct hydrocarbon patterns within the subcomplex. The T. sordida populations from Brazil and Argentina showed significantly different hydrocarbon profiles that posed concerns regarding the homogeneity of the species. Triatoma garciabesi had a more complex hydrocarbon pattern, but it shared some similarity with T. sordida. The quantitative and qualitative variations in the cuticular hydrocarbons may help to elucidate the relationships between species and populations of this insect group.

Genetic and Morphometric Variability of Triatoma sordida (Hemiptera: Reduviidae) from the Eastern and Western Regions of Paraguay

Triatoma sordida is widely distributed throughout the Chaco and the Eastern Region of Paraguay. It is associated to palm trees and artificial ecotopes located in peridomestic environments. The aim of this work was to determine genetic and morphometric variability and feeding behavior among population of T. sordida captured in domicile and peridomicile areas of Paraguay. Feeding contents and levels of genetic and morphometric variation were determined in 124 T. sordida from domicile and peridomicile populations of San Pedro and Paraguarí departments of the Eastern Region and Boquerón and Presidente Hayes departments of the Western region using Double Diffusion Gel, random amplified polymorphic DNA (RAPD), and head and wings morphometry. Morphometric analysis revealed isolation of populations by geographic region and larger size in triatomine populations from the Western Region. RAPD showed no specific patterns for domicile and peridomicile populations. The estimator of diversity (F ST; 0.08) and high gene flow obtained (N m; 5.7) did not allow the establishment of genetic differentiation within the same region. The blood meal source showed that poultry feeding was 38% of host preferences, and human blood was the second feeding preference (24%) in the insects from the Eastern Region while poultry feeding was predominant in those from the Western Region (30%). This work showed homogeneity between T. sordida populations of the same region and between domicile and peridomicile. The genetic diversity was determined among T. sordida populations of both geographical regions suggesting differentiation associated to eco-geographical isolation by distance. It is important to notice that pattern feedings were different between the two regions. Further studies should be focused on how phenetic and genetic variations could be related to the adaptation capacity of these triatomine populations to domicile, increasing their vector potentiality in the transmission of Chagas disease.

First report on C-banding, fluorochrome staining and NOR location in holocentric chromosomes of Elasmolomus (Aphanus) sordidus Fabricius, 1787 (Heteroptera, Rhyparochromidae)

In spite of various cytogenetic works on suborder Heteroptera, the chromosome organization, function and its evolution in this group is far from being fully understood. Cytologically, the family Rhyparochromidae constitutes a heterogeneous group differing in chromosome numbers. This family possesses XY sex mechanism in the majority of the species with few exceptions. In the present work, multiple banding techniques viz., C-banding, base-specific fluorochromes (DAPI/CMA₃) and silver nitrate staining have been used to cytologically characterize the chromosomes of the seed plant pest Elasmolomus (Aphanus) sordidus Fabricius, 1787 having 2n=12=8A+2m+XY. One pair of the autosomes was large while three others were of almost equal size. At diplotene, C-banding technique revealed, that three autosomal bivalents show terminal constitutive heterochromatic bands while one medium sized bivalent was euchromatic. Microchromosomes (m-chromosomes) were positively heteropycnotic. After DAPI and CMA₃ staining, all the autosomal bivalents showed equal fluorescence, except CMA₃ positive signals, observed at both telomeric heterochromatic regions of one medium sized autosomal bivalent. Silver nitrate staining further revealed that this chromosome pair carries Nucleolar Organizer Regions (NORs) at the location of CMA₃ positive signals. The X chromosome showed a thick C-band, positive to both DAPI /CMA₃ while Y, otherwise C-negative, was weakly positive to DAPI and negative to CMA₃, m-chromosomes were DAPI bright and CMA₃ dull.

Distribution of constitutive heterochromatin in two species of triatomines: Triatoma lenti Sherlock and Serafim (1967) and Triatoma sherlocki Papa, Jurberg, Carcavallo, Cerqueira & Barata (2002)

Triatoma lenti and Triatoma sherlocki are hemipterans that belong to the brasiliensis subcomplex. In triatomines, the constitutive heterochromatin pattern is species-specific and allows, in many cases, for the grouping of species. Thus, we cytogenetically analyzed T. sherlocki and T. lenti using C-banding, and we compared the results with previous ones obtained in other species of the brasiliensis subcomplex. Both species were found to have a male diploid chromosome number of 22 chromosomes (2n=20A+XY) with heterochromatic blocks at one or both chromosomal ends of all autosomal pairs. During early meiotic prophase, they showed a large heteropycnotic chromocenter constituted by the association of both sex chromosomes plus two autosomal pairs and many heterochromatic blocks dispersed inside the nucleus. All of these cytogenetic characteristics are similar to those observed in other species of brasiliensis subcomplex, results which confirm the grouping of T. sherlocki and T. lenti within this subcomplex. However, we emphasize the importance of other approaches, such as molecular analysis, to confirm the placement of T. lenti within the brasiliensis subcomplex.

Genetics and evolution of triatomines: from phylogeny to vector control

Triatomines are hemipteran bugs acting as vectors of the protozoan parasite Trypanosoma cruzi. This parasite causes Chagas disease, one of the major parasitic diseases in the Americas. Studies of triatomine genetics and evolution have been particularly useful in the design of rational vector control strategies, and are reviewed here. The phylogeography of several triatomine species is now slowly emerging, and the struggle to reconcile the phenotypic, phylogenetic, ecological and epidemiological species concepts makes for a very dynamic field. Population genetic studies using different markers indicate a wide range of population structures, depending on the triatomine species, ranging from highly fragmented to mobile, interbreeding populations. Triatomines transmit T. cruzi in the context of complex interactions between the insect vectors, their bacterial symbionts and the parasites; however, an integrated view of the significance of these interactions in triatomine biology, evolution and in disease transmission is still lacking. The development of novel genetic markers, together with the ongoing sequencing of the Rhodnius prolixus genome and more integrative studies, will provide key tools to expanding our understanding of these important insect vectors and allow the design of improved vector control strategies.

Geometric morphometrics and ecological niche modelling for delimitation of near-sibling triatomine species

Identifying morphologically similar triatomine species is key to Chagas' disease vector control and surveillance, but remains challenging when only qualitative phenotypic data are available. We investigated whether morphometric and ecological variation can provide additional criteria for species delimitation by combining geometric morphometrics and ecological niche modelling to characterize two near-sibling triatomine species, Triatoma sordida and Triatoma garciabesi (Reduviidae: Triatominae). We analysed size and shape variation in 231 wings and 123 heads from one T. garciabesi and three T. sordida populations. Predicted distribution maps (21 climatic variables, 324 vector occurrence points) were produced using the Maxent method. Multivariate analyses summarized morphological and ecological variation. Wings and heads of T. sordida were significantly larger and more elongated than those of T. garciabesi. Discriminant analyses separated the species, with a partial overlap between Argentinean populations. The predicted distribution of T. garciabesi included northwest Argentina (mainly arid Chaco), whereas that of T. sordida included northeast Argentina (humid Chaco) and the Brazilian Cerrado and Caatinga ecoregions. Clear ecological niche differences were observed, with T. garciabesi occupying colder and drier areas than T. sordida. Our results show how morphometric variation and niche divergence can be used to enhance operational criteria for the delimitation of phenotypically similar triatomine species.

Deciphering morphology in Triatominae: the evolutionary signals

Many species of Triatominae show evidence for morphological plasticity. Frequent taxonomic questions arose from this variability leading to disputes about describing new subspecies, species or even genera. We suggest this phenotypic flexibility is primarily an intraspecific feature, but with potential for evolutionary changes. We present arguments for a selection regime leading to the separation of species having low developmental canalization into morphologically distinct ecotypes. We suggest that these ecotypes, or morphs, or forms, may have evolutionary importance even if gene flow still exists between them. Thus, although we consider the morphological plasticity of Triatominae as an intraspecific trait, we defend the idea that it might represent a common evolutionary route to new species. Speciation processes in Triatominae could result from disruptive selection regimes combined with weak developmental canalization. Added to this basic pattern, accidental events could hasten evolutionary change. We suggest the heterosis as one of them.

Chromosome variability in the Chagas disease vector Rhodnius pallescens (Hemiptera, Reduviidae, Rhodniini)

Rhodnius pallescens is the main vector of Trypanosoma cruzi in Panama and one of the most relevant secondary vectors in Colombia. Despite the importance of this species, there is limited knowledge about the genetic variability along its geographical distribution. In order to evaluate the degree of karyotype variability we analyzed the meiotic behavior and banding pattern of the chromosomes of 112 males of R. pallescens coming from different regions of Colombia and Panama. Using the C-banding technique we identified two chromosomal patterns or cytotypes characterized by differences in the amount, size and distribution of constitutive heterochromatic regions in the chromosome complement (2n = 20 autosomes plus XY in males). The individuals can be easily classified in each cytotype by the analysis of the chromosomes during first meiotic prophase. The frequencies of the cytotypes are variable according to the geographic origin of the populations. This chromosomal divergence together with morphological data supports the existence of three genetically different populations of R. pallescens and provides new information to understand the distribution dynamics of this species.

Taxonomic study of the Phyllosoma complex and other triatomine (Insecta: Hemiptera: Reduviidae) species of epidemiological importance in the transmission of Chagas disease: Using ITS-2 and mtCytB sequences

The purpose of this work was to clarify the taxonomy and phylogenetic relationship of the Phyllosoma complex and other important vectors in Mexico. The internal transcribed spacer 2 (ITS-2) of rDNA and the cytochrome B gene of mtDNA (mtCytB) were analyzed for the following species of triatomine: Triatoma bassolsae, T. longipennis, T. mazzottii, T. mexicana, T. pallidipennis, T. picturata, and T. phyllosoma belonging to the Phyllosoma complex, as well as T. dimidiata, T. rubida, T. infestans, and Rhodnius prolixus. The results obtained with the analysis of the ITS-2 sequences showed that the Phyllosoma complex species could not be phylogenetically separated, since T. bassolsae and T. pallidipennis, as well as T. phyllosoma and T. mazzottii were indistinguishable. In contrast, the mtCytB gene separates each one of these triatomine species. The results support the proximity of all seven species currently included in the Phyllosoma complex as well as the exclusion of T. dimidiata. For the first time T. lecticularia and T. rubida were analyzed and were also shown to be related to the Phyllosoma complex.

Chromosomal variation and genome size support existence of cryptic species of Triatoma dimidiata with different epidemiological importance as Chagas disease vectors

The wide geographical distribution of Triatoma dimidiata, one of the three major vectors of Chagas disease, ranges from Mexico to northern Peru. Since this species occupies a great diversity of artificial and natural ecotopes, its eradication is extremely difficult. In order to assist control efforts, we used chromosome analyses and DNA amount as taxonomic markers to study genetic variability in populations of T. dimidiata from Mexico, Guatemala, El Salvador and Colombia. We differentiated three groups or cytotypes defined by characteristic chromosome C-banding patterns and genome size measured by flow cytometry. The three cytotypes are restricted to different geographic locations. Cytotype 1 occurs in Mexico (excluding Yucatán), Guatemala (excluding Petén), El Salvador and Colombia. Cytotype 2 occurs in Yucatán and cytotype 3 occurs in Petén. Cytotype 1, commonly associated with domestic and peridomestic environments but also inhabiting sylvatic ecotopes, is the most widespread and with major epidemiological significance. In contrast, the Yucatán cytotype inhabits wild ecotopes but increasingly enters houses, while the Petén cytotype appears exclusively sylvatic. We suggest that these cytotypes represent cryptic species of T. dimidiata with different epidemiological relevance as Chagas disease vectors. Poor ability to colonize human dwellings, together with their restricted geographic distribution, indicate that the Yucatán and Petén putative species probably have much less epidemiological significance than cytotype 1. Thus, the genetic markers we describe are powerful tools to differentiate cryptic species in T. dimidiata with different epidemiological significance, contributing to planning the most effective control measures.

Cytogenetic analysis of experimental hybrids in species of Triatominae (Hemiptera-Reduviidae)

A cytogenetic analysis was performed in experimental hybrids between species of Chagas disease transmitting bugs with remarkable differences in the amount and distribution of heterochromatin. Using C-banding technique, we identified the parental species chromosomes and analysed the meiotic behaviour in the male hybrids between Triatoma platensis and T. infestans, T. platensis and T. delpontei, and T. infestans and T. rubrovaria. The two former hybrids have an entirely normal meiotic behaviour despite the extensive differences in C-banded karyotypes observed in the parental species, indicating that heterochromatin differences between homeologous chromosomes are not a barrier that influences meiotic synapsis and recombination. On the contrary, the experimental hybrids between T. infestans and T. rubrovaria show failures in pairing of homeologous chromosomes that lead to the production of abnormal spermatids and hybrid sterility. Our data suggest that karyotypic repatterning within triatomines has involved at least two different pathways. Among closely related species, chromosomal changes have largely involved addition or deletion of heterochromatic regions. In more distant species, chromosomal rearrangements (i.e. inversions and translocations) have also arisen. Hybridisation data also allow to hypothesize about the origin and divergence of this taxonomic group, as well as the mechanisms that maintain species isolation.

Molecular research and the control of Chagas disease vectors

Chagas disease control initiatives are yielding promising results. Molecular research has helped successful programs by identifying and characterizing introduced vector populations and by defining intervention targets accurately. However, researchers and health officials are facing new challenges throughout Latin America. Native vectors persistently reinfest insecticide-treated households, and sylvatic triatomines maintain disease transmission in humid forest regions (including Amazonia) without colonizing human dwellings. In these scenarios, fine-scale vector studies are essential to define epidemiological risk patterns and clarify the involvement of little-known triatomine taxa in disease transmission. These eco-epidemiological investigations, as well as the planning and monitoring of control interventions, rely by necessity on accurate taxonomic judgments. The problems of cryptic speciation and phenotypic plasticity illustrate this need - and how molecular systematics can provide the fitting answers. Molecular data analyses also illuminate basic aspects of vector evolution and adaptive trends. Here we review the applications of molecular markers (concentrating on allozymes and DNA sequencing) to the study of triatomines. We analyze the suitability, strengths and weaknesses of the various techniques for taxonomic, systematic and evolutionary investigations at different levels (populations, species, and higher taxonomic categories).

Competition between vectors of Chagas disease, Triatoma infestans and T. sordida: effects on fecundity and mortality

Interspecific competition between two species of triatomine bugs (Hemiptera: Reduviidae), vectors of Chagas disease, was assessed for 16 months through comparative fecundity and mortality of experimental populations in chicken nests, maintained indoors with ambient conditions. Triatoma sordida (Stål), the secondary vector in north-eastern Argentina, was compared with Triatoma infestans (Klug) the more widespread domestic vector in the southern cone of South America. Both species populations originated from females collected in 1995 from the community of Empedrado, Corrientes, Argentina. Three population units were monitored: T. infestans alone, T. sordida alone and both species together in equal proportions. Each population started with six male and six female adults, 116 eggs, and nymphal instars I to V numbering 82, 48, 16, 11 and 19, respectively. Numbers and weight of individual bugs were recorded monthly (August 1995 to December 1996). The pure populations of T. infestans and T. sordida showed temporal changes in abundance, rising in summer and falling in winter, similar to the typical trends under normal field conditions. In the mixed population, however, T. sordida fell to extinction after 6 months, whereas T. infestans reached similar abundance to the pure (control) population. For each nymphal instar of T. sordida, the mean body weight was significantly less and mortality rate was higher in the mixed population compared to the pure population, but there were no significant differences of adult longevity or fecundity between the pure and mixed populations of T. sordida. The apparent competitive displacement of T. sordida by T. infestans was attributed to the latter species having better ability to obtain bloodmeals. This might explain the rarity of mixed populations where these two species occur in sympatry.

Phylogenetic relationships within the oliveirai complex (Hemiptera:Reduviidae:Triatominae)

The oliveirai complex is actually composed of nine related species of Triatominae that occur in the Pantanal ecosystem of Mato Grosso, Brazil. In order to confirm their specific status and infer their phylogenetic relationships, we performed a genetic and morphometric comparison concerning seven of the nine species of the complex. Isoenzyme analysis provided broadly similar phylogenetic information to that derived from discriminant analysis of size-free variables. The derived trees reveal two main species groups, one composed of three closed species (T. jurbergi, T. matogrossensis and T. vandae), and another one subdivided into two different pairs, the T. guazu-T. williami pair and the T. klugi-T. oliveirai pair. The results call the specific status of T. guazu and T. williami into question, support the possibility that the other analyzed species represent distinct taxa and query the existence of the oliveirai complex.

Chromosomal evolution trends of the genus Panstrongylus (Hemiptera, Reduviidae), vectors of Chagas disease

The genus Panstrongylus includes 14 species widely distributed from Mexico to Argentina, some of them with great epidemiological significance as vectors of Chagas disease. We study the karyotype and the male meiotic process of Panstrongylus chinai, P. geniculatus, P. herreri, P. lignarius, P. megistus, P. rufotuberculatus and P. tupynambai. All species present the same sex mechanism (X(1)X(2)Y in males and X(1)X(1)X(2)X(2) in females) and they also have 20 autosomes, with the exception of P. megistus that only presents 18 autosomes. The analysis of C-banding patterns and meiotic chromosome behaviour show a great level of variability allowing the identification of three clearly differentiated groups. In the first group, we only include P. megistus because of its unusual number of autosomes. The second group includes P. chinai, P. herreri, P. lignarius and P. rufotuberculatus. Their autosomes present terminal heterochromatic regions that appear scattered throughout the nucleus and associated with the sex chromosomes. Actually, P. herreri and P. lignarius can be considered cytogenetically identical. Our results are in agreement with morphological, ecological and molecular data indicating that they should be regarded as the same species. The third group only includes P. tupynambai that shows autosomes without C-positive regions. Panstrongylus geniculatus shares characters will all the three groups. Its karyotypic features are extremely polymorphic depending on their geographic origin. Some populations do not show any heterochromatic regions, while others exhibit few or several heterochromatic blocks. The chromosomal variability observed, together with its wide distribution and phenetic variability, suggest that P. geniculatus is a species complex comprising at least two distinct species. Considering the entire subfamily, the level of cytogenetic variation in Panstrongylus is lower than that observed in Triatoma but considerably more than that of Rhodnius, which is a very homogenous genus in terms of chromosome appearance and behaviour. This would endorse the closer relationship between Panstrongylus and Triatoma, and their divergence from Rhodnius, in accordance with current tribal classification.

Triatomine vectors of Trypanosoma cruzi: a molecular perspective based on nuclear ribosomal DNA markers

Chagas disease (American trypanosomiasis) is mainly transmitted by blood-sucking bugs of the reduviid subfamily Triatominae (Hemiptera: Prosorrhyncha). Control strategies are directed mainly against these insect vectors, as no vaccine is available and, except in the very early stage of infection, there is no effective chemótherapy. Studies of deoxyribonucleic acid (DNA) will lead to major advances in our knowledge of Triatominae and their relationships to Chagas disease transmission, epidemiology and control. Analyses of complete sequences of nuclear genes coding for ribosomal ribonucleic acid (rRNA) (rRNA genes) and spacers furnish significant information at the levels of higher taxons, genera, species, subspecies, hybrids, varieties and populations of Triatominae. This paper briefly reviews the contributions of studies on the slowly-evolving 18S or small subunit (SSU) rRNA gene and the quickly-evolving second internal transcribed spacer (ITS-2). The whole 18S rRNA gene is a useful marker for supraspecific relationships in Triatominae. ITS-2 is complementary to it, enabling resolution at specific and infraspecific levels. All the evidence suggests that ITS-2 will become the DNA marker of excellence for studies of Triatominae at specific and subspecific levels, as it is in other groups of organisms. Possible applications of data obtained from the study of rRNA and ITS-2 sequences of Triatominae are discussed.

Allozyme relationships among ten species of Rhodniini, showing paraphyly of Rhodnius including Psammolestes

Genetic relationships among 10 species of bugs belonging to the tribe Rhodniini (Hemiptera: Reduviidae), including some important vectors of Chagas disease, were inferred from allozyme analysis of 12 enzyme loci (out of 21 enzyme systems examined), using agarose gel electrophoresis. These species formed two clusters: one comprising Rhodnius brethesi, R. ecuadoriensis, R. pallescens and R. pictipes; the other with Psammolestes tertius, Rhodnius domesticus and the Rhodnius prolixus group comprising R. nasutus, R. neglectus, R. prolixus and R. robustus. The resulting tree was [((R. ecuadoriensis, R. pallescens) R. brethesi) R. pictipes], [R. domesticus (P. tertius [(R. nasutus, R. neglectus) (R. prolixus, R. robustus)])]. Rhodnius nasutus and R. neglectus differed by only one locus, whereas no diagnostic loci were detected between R. prolixus and R. robustus (22 loci were analysed for these four species), despite considerable DNA sequence divergence between species in each of these pairs. Allozymes of the R. prolixus group showed greater similarity with Psammolestes tertius than with other Rhodnius spp., indicating that Rhodnius is paraphyletic and might include Psammolestes.

Mitochondrial DNA sequences of triatomines (Hemiptera: Reduviidae): phylogenetic relationships

The phylogenetic relationships among 18 species of Triatominae were inferred based on mitochondrial DNA (mtDNA) sequences. The species of Triatoma included 11 belonging to the infestans complex [T. infestans (Klug), T. guasayana Wygodzinsky & Abalos, T. sordida (Stål), T. platensis Neiva, T. brasiliensis Neiva, T. rubrovaria (Blanchard), T. vitticeps (Stål), T. delpontei Romaña & Abalos, T. maculata (Erichson), T. patagonica Del Ponte, and T. matogrossensis Leite & Barbosa] and four others of the same genus but of different complexes [T. circummaculata (Stål), T. protracta (Uhler), T. dimidiata (Latreille), and T. mazzottii Usinger]. As possible outgroups we used Mepraia spinolai Mazza, Panstrongylus megistus (Burmeister), and Rhodnius prolixus Stål. We analyzed mtDNA fragments of the 12S and 16S ribosomal RNA genes from each of the 18 species, as well as of the cytochrome oxidase I (COI) gene from nine. The 12S, 16S, and COI gene sequences were analyzed individually and combined. All of the phylogenetic analyses unambiguously supported two clusters: one including T. infestans, T. platensis, and T. delpontei, and the other T. sordida and T. mutagrossensis. Inclusion of T. circummaculata into the infestans complex was confirmed, although this is in disagreement with the morphological classification. On the other hand, our analyses showed that T. dimidiata is closely related to a phylosoma complex species, T. mazzottii. This is consistent with the tentative classification previously made based on morphological characters. The issue of the monophyly of the genus Triatoma remains unresolved.

Molecular tools and triatomine systematics: a public health perspective

Triatomines, or kissing bugs, are vectors of Chagas disease to humans. This disease is a substantial public health problem affecting up to 12 million people throughout the Americas, and its control relies mainly on the insecticide treatment of triatomine-infested houses within villages. In this article, Fernando Monteiro, Ananias Escalante and Ben Beard review how molecular markers have been used to clarify triatomine systematics, and give examples of how our understanding of triatomine population structure and accurate vector identification can be used to optimize vector control.

Flight and nutritional status of sylvatic Triatoma sordida and Triatoma guasayana

Nutritional status relating to flight activity was investigated in natural populations of Triatoma sordida and T. guasayana during the dry season in the Bolivian Chaco. The peak flight activity of both species was unimodal and covered the period 61-180 min after sunset. The weight of insects was used as the indicator of nutritional status. Interspecies comparisons employing the same sex and type of capture showed a higher weight for T. guasayana. No significant difference according to weight was observed between flying insects and those collected in natural ecotopes (hollow trees and bromeliads). More than 87% of insects collected from natural ecotopes displayed flight ability under the study conditions, explaining their tendency to invade artificial structures during the dry season.

Chromosome homogeneity in populations of Triatoma brasiliensis Neiva 1911 (Hemiptera - reduviidae - triatominae)

Triatoma brasiliensis is the most important vector of Chagas disease in the semiarid zone of the Northeast of Brazil. Several authors have reported the occurrence of four chromatic patterns with morphological, ecological, and genetic differences. In order to determine the existence of cytogenetic differentiation between these chromatic forms, we analyzed their karyotypes and the chromosome behavior during the male meiotic process. Triatoma brasiliensis shows distinct and specific chromosome characteristics, which differ from those observed in all other triatomine species. However, no cytogenetic differences were observed between the four chromatic forms of T. brasiliensis. The lack of chromosome differentiation among them could indicate that the populations of this species are in a process of differentiation that does not involve their chromosomal organization.

Peridomestic distribution of Triatoma garciabesi and Triatoma guasayana in north-west Argentina

The Reduviid bugs Triatoma garciabesi Carcavallo et al. (Hemiptera: Reduviidae: Triatominae), previously known as T. sordida Ståhl in the semi-arid chaco region, and T. guasayana Wygodzinsky & Abalos, vectors of Trypanosoma cruzi Chagas (Kinetoplastida: Trypanosomatidae), were found to occupy wide but different ranges of ecotopes in the peridomestic environment. At Amamá and nearby rural villages in north-western Argentina, a combined total of 1233 specimens were collected from 325/2314 (14%) sites surveyed at 6-monthly intervals from November 1994 to November 1996. Triatoma garciabesi and T. guasayana displayed a significantly different distribution among peridomestic ecotopes. Triatoma garciabesi predominated over T. guasayana in the prevalence of infested sites, the number of colonies and the number of bugs collected. For T. garciabesi, the predominant ecotopes most likely to yield T. garciabesi repeatedly were the rugged bark of Prosopis alba or P. nigra (Fabaceae) trees, where chickens roosted, and chicken coops. For T. guasayana the main ecotopes were goat or sheep corrals, piled materials and orchard fences. Triatoma garciabesi and T. guasayana were collected concurrently from the same site on 9/2314 (0.4%) occasions, and on different dates at the same site on 12 (0.5%) occasions. The observed low frequency of mixed populations (< 1%) was not significantly different from that expected from a hypothesis of independence. Triatoma garciabesi clearly outnumbered T. guasayana in four of the nine mixed populations, none of which persisted as such. Neither T. garciabesi nor T. guasayana colonized human habitations, even in the absence of T. infestans (formerly the predominant domestic vector of T. cruzi in this area), a situation that apparently has not changed in the last 50 years in northern Argentina.

Triatominae as a model of morphological plasticity under ecological pressure

The use of biochemical and genetic characters to explore species or population relationships has been applied to taxonomic questions since the 60s. In responding to the central question of the evolutionary history of Triatominae, i.e. their monophyletic or polyphyletic origin, two important questions arise (i) to what extent is the morphologically-based classification valid for assessing phylogenetic relationships? and (ii) what are the main mechanisms underlying speciation in Triatominae? Phenetic and genetic studies so far developed suggest that speciation in Triatominae may be a rapid process mainly driven by ecological factors.

Mitochondrial DNA variation of Triatoma infestans populations and its implication on the specific status of T. melanosoma

DNA sequence comparison of 412 base-pairs fragments of the mitochondrial cytochrome B gene was used to infer the genetic structure of nine geographical Triatoma infestans populations and their phylogenetic relationship with T. melanosoma and T. brasiliensis. T. infestans and T. melanosoma were compared by morphometry, allozyme and cytogenetic analyses, as well as subjected to reciprocal crosses, in order to clarify the taxonomic status of the latter. No differences were found to distinguish the two species and the crosses between them yielded progeny. T. infestans populations presented four haplotypes that could be separated in two clusters: one formed by the samples from Bolivia (Andes and Chaco) and the other formed by samples from Argentina and Brazil. Silvatic and domestic T. infestans populations from Bolivia (Andes) were genetically identical.

Ecogenetics of Triatoma sordida and Triatoma guasayana (Hemiptera: reduviidae) in the Bolivian chaco

Triatoma guasayana and two putative cryptic species pertaining to T. sordida complex (named groups 1 and 2) occur in sympatry in the Bolivian Chaco. Using multilocus enzyme electrophoresis and subsequent genetic analysis, our work assesses their population distribution and dispersal capacity in domestic, peridomestic, and silvatic environments. Our collections by light trap in the silvatic environment indicated a predominance of T. guasayana and T. sordida group 2 and a lesser abundance of T. sordida group 1 ( pound 10% of the total of captures). Their similar distribution in two silvatic areas 80 km apart supports the hypothesis of their homogeneous dispersal through the Bolivian Chaco. The distribution of T. guasayana and T. sordida groups 1 and 2 was similar between silvatic environment and peridomestic ecotopes where 25% of positive places was occupied by two or three species. Bromeliads were confirmed as favorable shelter for T. guasayana but were free of T. sordida. T. sordida group 1 and to a lesser extent T. guasayana would be more invasive vectors for houses than T. sordida group 2. The spatial partition in the three species sampled in two distant sites suggested a reduced dispersive capacity.

Genetic structure of Triatoma sordida (Hemiptera: Reduviidae) domestic populations from Bolivia: application on control interventions

The genetic population of Triatoma sordida group 1, a secondary vector of Chagas disease in Bolivia, was studied by multi-locus enzyme electrophoresis. A total of 253 nymphal and adult specimens collected from seven neighbouring localities in the Velasco Province, Department of Santa Cruz, were processed. The relatively low genetic variability was confirmed for this species (rate of polymorphism: 0.20). The absence of genetic disequilibrium detected within the seven localities was demonstrated. A geographical structuration appears between localities with distances greater than 20 km apart. Although T. sordida presents a relatively reduced dispersive capacity, its panmictic unit is wider than compared with T. infestans. Genetic distances between T. sordida populations were correlated with geographic distance. Gene flow between geographic populations of T. sordida provides an efficient framework for effective vigilance and control protocols.

Cryptic speciation in Triatoma sordida (Hemiptera:Reduviidae) from the Bolivian Chaco

Eight natural Bolivian populations of two closely related species of Triatominae, Triatoma sordida and T. guasayana, were analysed by multilocus enzyme electrophoresis at 20 loci. Both species were readily separated and no natural hybrid was observed. Among the silvatic sample of T. sordida, strong departure from panmixia within and between loci was detected in two sites of the Chaco, suggesting two reproductively separate populations easily recognized at Idh2 and Mdh2 loci. Genetic distance between them was in agreement with the hypothesis of distinct species. However, the detection of 3% of putative hybrids suggested a recent evolutionary divergence.