A multiplex PCR assay that separates Rhodnius prolixus from members of the Rhodnius robustus cryptic species complex (Hemiptera: Reduviidae)

Geometric morphometry of the Rhodniusprolixus complex (Hemiptera, Triatominae): patterns of intraspecific and interspecific allometry and their taxonomic implications

In the subfamily Triatominae, the genus Rhodnius is one of the most studied, not only because of its epidemiological importance, but also because of the difficulty in differentiating its species. Currently, one of the strategies to control Chagas disease, besides other initiatives such as the analysis of donated blood, is focused on fighting the vector. Correctly identifying triatomines is essential for the entomoepidemiological surveillance of Chagas disease. The objective of the present work was to compare the species of the R.prolixus complex using geometric morphometry of hemelytra and heads to evaluate the patterns of intraspecific and interspecific allometry and their taxonomic implications. This method can help in the diagnosis of close species, whose morphological characteristics are insufficient for correct identification. Specimens from five different collections were used, covering the species included in the R.prolixus complex (R.barretti, R.dalessandroi, R.domesticus, R.marabaensis, R.milesi, R.montenegrensis, R.nasutus, R.neglectus, R.neivai, R.prolixus and R.robustus). Morphometric analyses indicated that the hemelytra are not structures with good resolution for separating species and, for this reason, the use of the heads proved to be more adequate for this group (thus allowing differentiation of all species of the R.prolixus complex). The results suggest that R.milesi is a variant of R.neglectus and confirms that R.prolixus and R.robustus are distinct species. Furthermore, we propose the creation of the R.neivai complex comprising R.domesticus and R.neivai.

Molecular detection of blood meal source up to three months since the last meal: Experimental starvation resistance in triatomines

The identification of Blood Meal Source (BMS) in hematophagous vectors contributes to a better understanding of the ecology of hemoparasite transmission. Those insects can endure long periods without feeding, waiting for a favorable setting. Although this represents an important behavior observed in those groups, such as triatomines, little is known about how time can affect BMS detection, especially considering extended periods. To comprehend to which extent this behavioral phenomenon can impact molecular detection, we submitted two groups of Rhodnius robustus to increasing periods of starvation under experimental conditions. It was possible to recover the BMS until the 12th week of the starvation process. Nymphs were more resistant to prolonged periods of starvation (up to more than 189 days) than adults (maximum of 137 days), with no significant difference between their weights after being fed. The study brought new insights to the understanding of Trypanosoma cruzi transmission by R. robustus in the nature, with a temporal perspective.

Experimental infection of Rhodnius robustus Larrousse, 1927 (Hemiptera, Reduviidae, Triatominae) with Trypanosoma cruzi (Chagas, 1909) (Kinetoplastida, Trypanosomatidae) IV

Vector competence of triatomines (kissing bugs) for Trypanosoma cruzi transmission depends on the parasite-vector interaction and the genetic constitution of both. This study evaluates the susceptibility and vector competence of Rhodnius robustus experimentally infected with T. cruzi IV (TcIV). Nymphs were fed on infected mice or an artificial feeder with blood containing culture-derived metacyclic trypomastigotes (CMT) or blood trypomastigotes (BT). The intestinal contents (IC) and excreta of the insects were examined by fresh examination and kDNA-PCR. The rate of metacyclogenesis was also determined by differential counts. Fifth instar nymphs fed with CMT ingested a greater blood volume (mean of 74.5 μL) and a greater amount of parasites (mean of 149,000 CMT/μL), and had higher positivity in the fresh examination of the IC. Third instar nymphs fed with CMT had higher positivity (33.3%) in the fresh examination of the excreta. On the 20th day after infection (dai), infective metacyclic trypomastigote (MT) forms were predominant in the excreta of 3/4 experimental groups, and on the 30th dai, the different parasitic forms were observed in the IC of all the groups. Higher percentages of MT were observed in the excreta of the 5th instar nymphs group (84.1%) and in the IC of the 3rd instar nymphs group (80.0%). Rhodnius robustus presented high susceptibility to infection since all nymphs were infected, regardless of the method used for blood meal, in addition these insects demonstrated vector competence for TcIV with high rates of metacyclogenesis being evident.

Species-specific patterns of shelter exploitation in Chagas disease vectors of the genus Rhodnius

Triatomines are insect vectors of Trypanosoma cruzi¸ the etiological agent of Chagas disease. Several species belonging to the genus Rhodnius (Hemiptera: Reduviidae) have been reported inhabiting domestic and peridomestic environments in different regions of Latin America. However, behavioral and sensory ecology aspects related to their use of shelters have been poorly studied. The objective of the present study was to characterize how bug density, illumination and thigmotactic information affect the use of shelters by three species belonging to the Rhodnius prolixus species complex. We evaluated whether exposure to different insect densities affects the proportion of R. prolixus, Rhodnius robustus and Rhodnius neglectus that choose to stay inside a refuge. Besides, we evaluated whether absence of an illumination regime affects their tendency to hide in shelters. Our results showed that the proportion of individuals that remained outside the shelter increased with rising insect densities. Nevertheless, while R. prolixus only reacted by augmenting this proportion with the highest density tested, the other species showed significant increases already at lower densities. On the other hand, a significantly higher number of R. robustus stayed outside the shelter in the absence of a light cycle, while no change was induced for the other species. Thus, this study determined species-specific profiles of refuge exploitation defined by factors such as thigmotaxis and negative phototaxis. The differences observed among these Rhodnius species may impact their house colonization abilities, which seem to be critically affected by bug hiding performance during health service detection processes.

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.

Dehydration-Stress Resistance in Two Sister, Cryptic Rhodnius Species-Rhodnius prolixus and Rhodnius robustus Genotype I (Hemiptera: Reduviidae)

Rhodnius prolixus Stål, a major Chagas disease vector, often colonizes in houses, whereas its sister species, Rhodnius robustus Larrousse genotype I, does not colonize in houses and has little medical relevance. Factors potentially underlying this crucial difference remain largely uncharted. The 'microclimate-adaptation hypothesis' notes that R. prolixus is adapted to the dry microclimate of small-crowned Copernicia palms, whereas R. robustus I exploits the high-moisture microclimate of large-crowned Attalea and Acrocomia. Hence, R. prolixus, but not R. robustus I, would be (pre)adapted to the relatively dry microclimate typical of man-made habitats. This hypothesis predicts that, while severe dehydration should harm both species similarly, R. prolixus should withstand moderate-to-mild dehydration stress better than R. robustus I. To test this prediction, we compared fitness metrics of genotyped R. prolixus and R. robustus I kept at 28°C and under severe (20% relative humidity, RH), moderate (40% RH), or mild dehydration stress (75% RH). Egg-hatching success increased with decreasing dehydration stress in R. robustus I (0% → 19% → 100%), but was high across treatments in R. prolixus (78% → 100% → 100%). Both species underwent high, early mortality under severe dehydration; under moderate and mild stress, R. prolixus experienced less mortality and survived longer than R. robustus I. Our results suggest that adaptation to distinct palm-crown microclimates may partly underlie the so far unexplained differences in house-colonization ability among Rhodnius Stål species. Experimental replication across additional species/populations will be required to further probe this adaptive hypothesis-which, if supported, may also provide insight into the likely responses of Chagas disease vectors to climate change.

Transcriptome-based molecular systematics: Rhodnius montenegrensis (Triatominae) and its position within the Rhodnius prolixus-Rhodnius robustus cryptic-species complex

BACKGROUND

Rhodnius montenegrensis (Triatominae), a potential vector of Chagas disease, was described after R. robustus-like bugs from southwestern Amazonia. Mitochondrial cytb sequence near-identity with sympatric R. robustus (genotype II) raised doubts about the taxonomic status of R. montenegrensis, but comparative studies have reported fairly clear morphological and genetic differences between R. montenegrensis and laboratory stocks identified as R. robustus. Here, we use a transcriptome-based approach to investigate this apparent paradox.

RESULTS

We retrieved publicly-available transcriptome sequence-reads from R. montenegrensis and from the R. robustus stocks used as the taxonomic benchmark in comparative studies. We (i) aligned transcriptome sequence-reads to mitochondrial (cytb) and nuclear (ITS2, D2-28S and AmpG) query sequences (47 overall) from members of the R. prolixus-R. robustus cryptic-species complex and related taxa; (ii) computed breadth- and depth-coverage for the 259 consensus sequences generated by these alignments; and, for each locus, (iii) appraised query sequences and full-breadth-coverage consensus sequences in terms of nucleotide-sequence polymorphism and phylogenetic relations. We found evidence confirming that R. montenegrensis and R. robustus genotype II are genetically indistinguishable and, hence, implying that they are, in all likelihood, the same species. Furthermore, we found compelling genetic evidence that the benchmark 'R. robustus' stocks used in R. montenegrensis description and in later transcriptome-based comparisons are in fact R. prolixus, although likely mixed to some degree with R. robustus (probably genotype II, a.k.a. R. montenegrensis).

CONCLUSIONS

We illustrate how public-domain genetic/transcriptomic data can help address challenging issues in disease-vector systematics. In our case-study, taxonomic confusion apparently stemmed from the misinterpretation of sequence-data analyses and misidentification of taxonomic-benchmark stocks. More generally, and together with previous reports of mixed and/or misidentified Rhodnius spp. laboratory colonies, our results call into question the conclusions of many studies (on morphology, genetics, physiology, behavior, bionomics or interactions with microorganisms including trypanosomes) based on non-genotyped 'R. prolixus' or 'R. robustus' stocks. Correct species identification is a prerequisite for investigating the factors that underlie the physiological, behavioral or ecological differences between primary domestic vectors of Chagas disease, such as R. prolixus, and their sylvatic, medically less-relevant relatives such as R. robustus (s.l.) including R. montenegrensis.

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.

MALDI-TOF MS protein profiling for the rapid identification of Chagas disease triatomine vectors and application to the triatomine fauna of French Guiana

Triatomines are haematophagous insects involved in the transmission of Trypanosoma cruzi, the aetiological agent of Chagas disease. The vector competence of these arthropods can be highly variable, depending on the species. A precise identification is therefore crucial for the epidemiological surveillance of T. cruzi and the determination of at-risk human populations. To circumvent the difficulties of morphological identification and the lack of comprehensiveness of the GenBank database, we hereby propose an alternative method for triatomine identification. The femurs of the median legs of triatomines from eight different species from French Guiana were subjected to matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) analysis. Method evaluation was performed on fresh specimens and was applied to dry specimens collected between 1991 and 2003. Femur-derived protein extracts provided reproducible spectra within the same species along with significant interspecies heterogeneity. Validation of the study by blind test analysis provided 100% correct identification of the specimens in terms of the species, sex and developmental stage. MALDI-TOF mass spectrometry appears to be a powerful tool for triatomine identification, which is a major step forward in the fight against Chagas disease.

The Evolutionary Origin of Diversity in Chagas Disease Vectors

Chagas disease is amongst the ten most important neglected tropical diseases but knowledge on the diversification of its vectors, Triatominae (Hemiptera: Reduviidae), is very scarce. Most Triatominae species occur in the Americas, and are all considered potential vectors. Despite its amazing ecological vignette, there are remarkably few evolutionary studies of the whole subfamily, and only one genome sequence has been published. The young age of the subfamily, coupled with the high number of independent lineages, are intriguing, yet the lack of genome-wide data makes it a challenge to infer the phylogenetic relationships within Triatominae. Here we synthesize what is known, and suggest the next steps towards a better understanding of how this important group of disease vectors came to be.

Rhodnius prolixus and R. robustus (Hemiptera: Reduviidae) nymphs show different locomotor patterns on an automated recording system

BACKGROUND

Circadian rhythms of triatomines, vectors of the etiological agent Trypanosoma cruzi responsible for Chagas disease, have been extensively studied in adults of the two most epidemiologically relevant vector species, Rhodnius prolixus and Triatoma infestans. However, little attention has been dedicated to the activity patterns in earlier developmental stages, even though triatomine nymphs are equally capable of transmitting T. cruzi to humans. Because circadian rhythms may differ even between closely related species, studies that focus on this behavioral trait can also be used to shed light on the taxonomy of controversial taxa, which becomes especially relevant regarding vector species.

METHODS

We compared the daily locomotor activity patterns of second- and third-instar nymphs of Rhodnius prolixus and Rhodnius robustus in order to unveil possible behavioral differences between these cryptic species. Mitochondrial and nuclear markers were sequenced to confirm species identification.

RESULTS

Nymphs of both species had a bimodal pattern of locomotion and similar daily activity patterns, but R. prolixus is more active under light/dark cycles and depicts a more pronounced activity rhythm under constant darkness conditions.

CONCLUSIONS

We describe the implementation of an often-used automated method for the recording of individual locomotor activity to differentiate sibling species of Rhodnius with distinct epidemiological relevance. The higher levels of activity observed in the nymphs of R. prolixus could potentially contribute to increased vector capacity.

Chitin is a component of the Rhodnius prolixus midgut

Chitin is an essential component of the peritrophic matrix (PM), which is a structure that lines the insect's gut and protects against mechanical damage and pathogens. Rhodnius prolixus (Hemiptera: Reduviidae) does not have a PM, but it has an analogous structure, the perimicrovillar membrane (PMM); chitin has not been described in this structure. Here, we show that chitin is present in the R. prolixus midgut using several techniques. The FTIR spectrum of the KOH-resistant putative chitin-material extracted from the midgut bolus showed peaks characteristic of the chitin molecule at 3500, 1675 and 1085 cm(1). Both the midgut bolus material and the standard chitin NMR spectra showed a peak at 1.88 ppm, which is certainly due to methyl protons in the acetamide a group. The percentages of radioactive N-acetylglucosamine (CPM) incorporated were 2 and 4% for the entire intestine and bolus, respectively. The KOH-resistant putative chitin-material was also extracted and purified from the N-acetylglucosamine radioactive bolus, and the radioactivity was estimated through liquid scintillation. The intestinal CHS cDNA translated sequence was the same as previously described for the R. prolixus cuticle and ovaries. Phenotypic alterations were observed in the midgut of females with a silenced CHS gene after a blood meal, such as retarded blood meal digestion; the presence of fresh blood that remained red nine days after the blood meal; and reduced trachea and hemozoin content compared with the control. Wheat germ agglutinin (a specific probe that detects chitin) labeling proximal to the intestine (crop and midgut) was much lower in females with a silenced CHS gene, especially in the midgut region, where almost no fluorescence signal was detected compared with the control groups. Midguts from females with a CHS gene silenced by dsRNA-CHS and control midguts pre-treated with chitinase showed that the chitin-derived fluorescence signal decreased in the region around the epithelium, the region facing the midgut and projections towards the intestinal lumen when evaluated microscopically. The relative reduction in CHS transcripts by approximately 80% using an RNAi assay supports the phenotypical alterations in the midgut observed using fluorescence microscopy assays. These data show that chitin is present in the R. prolixus midgut epithelium and in its surface projections facing the lumen. The CHS gene expression and the presence of chitin in the R. prolixus midgut may suggest a target for controlling Chagas disease vectors and addressing this public health problem.

Rhodnius barretti, a new species of Triatominae (Hemiptera: Reduviidae) from western Amazonia

Rhodnius barretti , a new triatomine species, is described based on adult specimens collected in rainforest environments within the Napo ecoregion of western Amazonia (Colombia and Ecuador). R. barretti resembles Rhodnius robustus s.l. , but mitochondrial cytochrome b gene sequences reveal that it is a strongly divergent member of the “robustus lineage”, i.e., basal to the clade encompassing Rhodnius nasutus , Rhodnius neglectus , Rhodnius prolixus and five members of the R. robustus species complex. Morphometric analyses also reveal consistent divergence from R. robustus s.l. , including head and, as previously shown, wing shape and the length ratios of some anatomical structures. R. barretti occurs, often at high densities, in Attalea butyracea and Oenocarpus bataua palms. It is strikingly aggressive and adults may invade houses flying from peridomestic palms. R. barretti must therefore be regarded as a potential Trypanosoma cruzi vector in the Napo ecoregion, where Chagas disease is endemic.

Triatominae species of Suriname (Heteroptera: Reduviidae) and their role as vectors of Chagas disease

Nine species of Triatominae, representing three tribes and five genera, are currently known in Suriname. An annotated list of the species based on the collections of the Bureau of Public Health (Suriname), the National Zoological Collection Suriname and the National History Museum Leiden (the Netherlands) is provided. Additionally, the results of several years of opportunistic collection in two domestic environments are presented. The most common species are Rhodnius pictipes Stål, 1972, Rhodnius robustus Larrouse, 1972 and Panstrongylus geniculatus (Latreille, 1811). The significance of the species as vectors of Chagas disease in Suriname is discussed.

Evolutionary relationships of the Triatoma matogrossensis subcomplex, the endemic triatoma in Central-Western Brazil, based on mitochondrial DNA sequences

The phylogenetic relationships among species of Triatoma matogrossensis subcomplex ( T. baratai, T. guazu, T. matogrossensis, T. sordida, T. vandae, and T. williami) was addressed by using fragments of cytochrome oxidase I (COI), 16S rDNA (16S), and cytochrome b (Cytb) through Bayesian and parsimony analyses. We did not recover a monophyletic T. matogrossensis subcomplex, and their members were found clustered in three strongly supported clades, as follows: i) T. jurbergi + T. matogrossensis + T. vandae + T. garciabesi + T. sordida; ii) with T. guasayana as the sister group of clade (i); and iii) T. williami + T. guazu, however not closely related to the clade formed by the previously mentioned species. The other two endemic species from Central-Western Brazil, T. baratai and T. costalimai, were not recovered with strong clade support as related to other members of this subcomplex. Results call for a further revision in the classification of the subcomplexes within the genus Triatoma.

A nuclear single-nucleotide polymorphism (SNP) potentially useful for the separation of Rhodnius prolixus from members of the Rhodnius robustus cryptic species complex (Hemiptera: Reduviidae)

The design and application of rational strategies that rely on accurate species identification are pivotal for effective vector control. When morphological identification of the target vector species is impractical, the use of molecular markers is required. Here we describe a non-coding, single-copy nuclear DNA fragment that contains a single-nucleotide polymorphism (SNP) with the potential to distinguish the important domestic Chagas disease vector, Rhodnius prolixus, from members of the four sylvatic Rhodnius robustus cryptic species complex. A total of 96 primer pairs obtained from whole genome shotgun sequencing of the R. prolixus genome (12,626 random reads) were tested on 43 R. prolixus and R. robustus s.l. samples. One of the seven amplicons selected (AmpG) presented a SNP, potentially diagnostic for R. prolixus, on the 280th site. The diagnostic nature of this SNP was then confirmed based on the analysis of 154 R. prolixus and R. robustus s.l. samples representing the widest possible geographic coverage. The results of a 60% majority-rule Bayesian consensus tree and a median-joining network constructed based on the genetic variability observed reveal the paraphyletic nature of the R. robustus species complex, with respect to R. prolixus. The AmpG region is located in the fourth intron of the Transmembrane protein 165 gene, which seems to be in the R. prolixus X chromosome. Other possible chromosomal locations of the AmpG region in the R. prolixus genome are also presented and discussed.

Geographic distribution of chagas disease vectors in Brazil based on ecological niche modeling

Although Brazil was declared free from Chagas disease transmission by the domestic vector Triatoma infestans, human acute cases are still being registered based on transmission by native triatomine species. For a better understanding of transmission risk, the geographic distribution of Brazilian triatomines was analyzed. Sixteen out of 62 Brazilian species that both occur in >20 municipalities and present synanthropic tendencies were modeled based on their ecological niches. Panstrongylus geniculatus and P. megistus showed broad ecological ranges, but most of the species sort out by the biome in which they are distributed: Rhodnius pictipes and R. robustus in the Amazon; R. neglectus, Triatoma sordida, and T. costalimai in the Cerrado; R. nasutus, P. lutzi, T. brasiliensis, T. pseudomaculata, T. melanocephala, and T. petrocchiae in the Caatinga; T. rubrovaria in the southern pampas; T. tibiamaculata and T. vitticeps in the Atlantic Forest. Although most occurrences were recorded in open areas (Cerrado and Caatinga), our results show that all environmental conditions in the country are favorable to one or more of the species analyzed, such that almost nowhere is Chagas transmission risk negligible.

Morphometric and molecular differentiation of a Rhodnius robustus-like form from R. robustus Larousse, 1927 and R. prolixus Stal, 1859 (Hemiptera, Reduviidae)

In Triatominae, "robustus" group constitutes a cluster of species with great haplotypic divergences but high similarities at morphological and nuclear DNA levels. Given these similarities, species identification generates a frequently problematic issue. In northwestern Amazonia, Rhodnius robustus cohabit with an apparently new species, cryptic with R. robustus (Abad-Franch and Monteiro, 2005). In this region (municipality of Puerto Asís, Department of Putumayo, Colombia), we collected insects classified as R. robustus by traditional keys. We compared this sample with specimens of R. robustus from Venezuela, and of R. prolixus from Colombia and Venezuela. The comparisons used landmark-based geometric morphometrics, and analyses of mitochondrial cytochrome b gene and of D2 variable region of the 28S RNA. The shape of the wings from Puerto Asís specimens disclosed clear-cut divergence from the shape of the wings as found for R. prolixus specimens from Venezuela and Colombia, and diverged from the shape of R. robustus from Venezuela. Thus, morphometric analyses suggested that the Puerto Asís collection could represent a new taxon. Using R. pallescens as an outgroup, a tentative phylogenetic tree based on the geometry of the wing showed the Rhodnius from Puerto Asís more similar to the R. prolixus from Colombia than their congeners from Venezuela. In contrast, the molecular classification clustered Colombian R. prolixus and Venezuelan R. robustus with published GenBank sequences, but it gave the insects from Puerto Asís a basal position to the "robustus" group. This outcome suggests that the Puerto Asís haplotype could be the one found by Abad-Franch and Monteiro (2005). Thus, both morphometric and molecular markers used here, although differing in the phylogenetic classification of samples, could differentiate the Puerto Asís sample from the morphologically similar R. prolixus and R. robustus. This could represent a valuable help in the entomological surveillance related to the control of Chagas disease in the South of Colombia and North of Ecuador.

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.

The triatominae species of French Guiana (Heteroptera: Reduviidae)

An annotated list of the triatomine species present in French Guiana is given. It is based on field collections carried out between 1993-2008, museum collections and a literature review. Fourteen species, representing four tribes and six genera, are now known in this country and are illustrated (habitus). Three species are recorded from French Guiana for the first time: Cavernicola pilosa, Microtriatoma trinidadensis and Rhodnius paraensis. The two most common and widely distributed species are Panstrongylus geniculatus and Rhodnius pictipes. The presence of two species (Panstrongylus megistus and Triatoma maculata) could be fortuitous and requires confirmation. Also, the presence of Rhodnius prolixus is doubtful; while it was previously recorded in French Guiana, it was probably mistaken for R. robustus. A key for French Guiana's triatomine species is provided.

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.

Populations, hybrids and the systematic concepts of species and subspecies in Chagas disease triatomine vectors inferred from nuclear ribosomal and mitochondrial DNA

In Chagas disease, triatomine vectors are the main target for control measures because of the absence of effective drugs. The broad usefulness of nuclear rDNA and mtDNA sequences explains why triatomine studies using these markers have increased so pronouncedly in recent years. This indicates the appropriateness of an updated review about these molecular markers, concentrating on aspects useful for research on Chagas disease vectors. A comparative analysis is presented on the efficiency, weight of their different characteristics, limitations and problems of each of the different DNA markers in the light of the results obtained in studies on populations, hybrids, subspecies and species of the subfamily Triatominae. The use of a standardized composite haplotype code nomenclature for both nuclear rDNA and mtDNA markers is strongly encouraged to avoid difficulties in comparative studies. Triatomine aspects related to concerted evolution, microsatellites, minisatellites and insertions/deletions in nuclear rDNA and silent/non-silent mutations, pseudogenes and weaknesses of partial sequences in mtDNA are analysed. Introgression and hybrids, nuclear and mitochondrial DNA strengths, and compared evolutionary rates of nuclear rDNA and mtDNA in triatomines are discussed. Many conclusions are obtained thanks to the availability, for the first time in triatomines, of a complete sequence of a protein-coding mtDNA gene as ND1 from very numerous triatomine species covering from different populations of a species up to members belonging to different tribes. The evolutionary rates of each nuclear rDNA marker and mtDNA marker are analysed by comparison at subspecies level (intrapopulational, interpopulational, between morphs, and between subspecies) and species level (close and distant species of the same genus, species of different genera, and species of different tribes). Weaknesses of mtDNA for systematic-taxonomic purposes detected recently and newly in insects and triatomines, respectively, are discussed in detail. Emphasis is given to taxonomic units and biological entities presenting well-known problematics, both from the systematic-taxonomic and/or epidemiological-control points of view, as well as to molecular situations which can give rise to erroneous conclusions. All these aspects constitute the background on which the key question about the systematic concepts of species and subspecies in triatomines is focused. The global purpose is to facilitate future work on triatomines by highlighting present gaps, how better choice the appropriate markers, and marker aspects which should be taken into account. Key characteristics as alpha, CI and transformation rate matrices ought to be obtained and noted to get appropriate results and allow correct interpretations. The main aim is to offer a baseline for future fundamental research on triatomines and applied research on transmission, epidemiology and control measures related to Chagas disease vectors.

Classification, evolution, and species groups within the Triatominae

Classification of the Triatominae has become a complex balance between traditional approaches and a wide variety of evolutionary interpretations. On the one hand is the need for a stable classification of practical use for those involved in vector surveillance and control. On the other is the desire to adequately reflect evolutionary theory derived from a range of molecular, cytogenetic and morphometric comparisons, with additional complications raised by current interpretations of the subfamily as a recently derived polyphyletic assemblage. Here we review key aspects of triatomine systematics and evolution, to derive a pragmatic classification that seeks to build on traditional morphological concepts within the context of current evolutionary theories.

Is Rhodnius prolixus (Triatominae) invading houses in central Brazil?

Sylvatic triatomines of the genus Rhodnius commonly fly into houses in Latin America, maintaining the risk of Chagas disease transmission in spite of control efforts. In the recent past, adult bugs collected inside houses in central Brazil were identified as R. prolixus, a primary disease vector whose natural geographical range excludes this region. Three nearly sibling species (R. neglectus, R. nasutus, and R. robustus), secondary vectors with limited epidemiological significance, occur naturally south of the Brazilian Amazon. The specific status of Rhodnius specimens found inside houses in central Brazil is therefore an epidemiologically important (and still debated) issue. We used wing and head geometric morphometrics to investigate the taxonomic status of 230 adult specimens representing all four 'R. prolixus group' species (19 populations from palm trees, domiciles, and reference laboratory colonies). Discriminant analyses of shape variation allowed for an almost perfect reclassification of individuals to their putative species. Shape patterning revealed no consistent differences between most specimens collected inside houses in central Brazil and R. neglectus, and showed that R. robustus and R. neglectus occur sympatrically (and fly into houses) in southern Amazonia. Furthermore, all Brazilian specimens clearly differed from our reference R. prolixus population. Using geometric morphometrics, we confidently ascribed individual triatomines to their species within the problematic 'R. prolixus group', illustrating the potential value of this approach in entomological surveillance. Our results strongly support the idea that R. neglectus, and not R. prolixus, is the species invading houses in central Brazil.

Microsatellite markers from the Chagas disease vector, Rhodnius prolixus (Hemiptera, Reduviidae), and their applicability to Rhodnius species

Ten microsatellites were isolated and characterized from a partial genomic library of Rhodnius prolixus, the principal Chagas disease vector in Venezuela, Colombia and Central America. These polymorphic molecular markers could be particularly useful in Chagas disease control initiatives. A wider applicability of the primer-pairs isolated was shown, from 6 to 10 loci being amplifiable in five out of the ten Rhodnius species tested, namely R. domesticus, R. nasutus, R. neglectus, R. neivai and R. robustus. Interestingly, all the loci were amplified in the latter. These markers may be of interest to trace the colonization of human dwellings from triatomine sylvatic populations in order to better define epidemiological risk patterns.

Biogeography and evolution of Amazonian triatomines (Heteroptera: Reduviidae): implications for Chagas disease surveillance in humid forest ecoregions

An ecological-evolutionary classification of Amazonian triatomines is proposed based on a revision of their main contemporary biogeographical patterns. Truly Amazonian triatomines include the Rhodniini, the Cavernicolini, and perhaps Eratyrus and some Bolboderini. The tribe Rhodniini comprises two major lineages (pictipes and robustus). The former gave rise to trans-Andean (pallescens) and Amazonian (pictipes) species groups, while the latter diversified within Amazonia (robustus group) and radiated to neighbouring ecoregions (Orinoco, Cerrado-Caatinga-Chaco, and Atlantic Forest). Three widely distributed Panstrongylus species probably occupied Amazonia secondarily, while a few Triatoma species include Amazonian populations that occur only in the fringes of the region. T. maculata probably represents a vicariant subset isolated from its parental lineage in the Caatinga-Cerrado system when moist forests closed a dry trans-Amazonian corridor. These diverse Amazonian triatomines display different degrees of synanthropism, defining a behavioural gradient from household invasion by adult triatomines to the stable colonisation of artificial structures. Anthropogenic ecological disturbance (driven by deforestation) is probably crucial in the onset of the process, but the fact that only a small fraction of species effectively colonises artificial environments suggests a role for evolution at the end of the gradient. Domestic infestation foci are restricted to drier subregions within Amazonia; thus, populations adapted to extremely humid rainforest microclimates may have limited chances of successfully colonising the slightly drier artificial microenvironments. These observations suggest several research avenues, from the use of climate data to map risk areas to the assessment of the synanthropic potential of individual vector species.