Similarity of the patterns of sensilla on the antennae of Triatoma melanosoma and Triatoma infestans

The Olfactory Chemosensation of Hematophagous Hemipteran Insects

As one of the most abundant insect orders on earth, most Hemipteran insects are phytophagous, with the few hematophagous exceptions falling into two families: Cimicidae, such as bed bugs, and Reduviidae, such as kissing bugs. Many of these blood-feeding hemipteran insects are known to be realistic or potential disease vectors, presenting both physical and psychological risks for public health. Considerable researches into the interactions between hemipteran insects such as kissing bugs and bed bugs and their human hosts have revealed important information that deepens our understanding of their chemical ecology and olfactory physiology. Sensory mechanisms in the peripheral olfactory system of both insects have now been characterized, with a particular emphasis on their olfactory sensory neurons and odorant receptors. This review summarizes the findings of recent studies of both kissing bugs (including Rhodnius prolixus and Triatoma infestans) and bed bugs (Cimex lectularius), focusing on their chemical ecology and peripheral olfactory systems. Potential chemosensation-based applications for the management of these Hemipteran insect vectors are also discussed.

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.

Inferences about antennal phenotype: the "Triatoma maculata complex" (Hemiptera: Triatominae) is valid?

The "Triatoma maculata complex" is presently formed by two epidemiologically important species of Triatominae, Triatoma maculata and Triatoma pseudomaculata, which share morphologic and chromatic characteristics. In order to clarify the systematic status and infer the evolutionary relationships of these vectors of Chagas disease, we performed a comparative analysis of their antennal phenotype, taking also into account Triatoma wygodzinskyi, a possible sister species. The comparison was based on sensilla arrays on the three distal segments of the antenna. Our results show a close similarity between T. pseudomaculata and T. wygodzinskyi antennal phenotypes, and significant differences with T. maculata. The inter-population study reinforces the idea that T. pseudomaculata (arboricolous species) and T. wygodzinskyi (rupicolous species) would originate from a common ancestor.

Phenotypic variability associated to genomic changes in the main vector of Chagas disease in the southern cone of South America

This study shows for the first time, the relationship between chromosomic and meristic quantitative characters of Triatoma infestans, the main vector of Chagas disease in the southern cone of South America. The antennal phenotype of 225 adults from five countries and three cytotypes, were analyzed using univariate and multivariate techniques. The study found a clear association between cytotypes and antennal phenotypes. The complexity of the antennal sensilla pattern was higher in the non-Andean cytotype, showing more chemoreceptors usually linked to sexual behaviour, host finding and flight. The phenetic differences were more notorious on females than on males. Changes in the sexual dimorphism were detected, being the differences most notorious in the non-Andean cytotype. Similitude of the geographic populations using the antennal phenotype coincides with environmental gradient of the area, showing a close association between the physical features of the living zones and quantitative traits of the vectors. The epidemiological implications of the phenetic differences observed in the study are discussed.

Association between antennal phenotype, wing polymorphism and sex in the genus Mepraia (Reduviidae: Triatominae)

Mepraia spinolai and Mepraia gajardoi (Hemiptera, Reduviidae) are only found in the arid regions of northern Chile. Mepraia is the only genus of Triatominae with marked wing polymorphism. Females of both species are micropterous, males of M. spinolai may be micropterous, brachypterous or macropterous, while males of M. gajardoi are always brachypterous. Because of this wing polymorphism, Mepraia can be used as a model to analyze morphological adaptations related to the flying activity and evolutionary relationships in the Triatominae. The study presented here analyses the antennal phenotype of the Mepraia species and carries out a comparison with the two species of Triatoma included in the spinolai complex (Triatoma eratyrusiformis and Triatoma breyeri). The analysis of the antennal phenotype of Mepraia showed a marked intraspecific phenotypic variability related with sex and wing condition. The number and length of multiporous trichoid sensilla (TH) on the pedicel are significantly higher and longer in winged males and are strongly reduced in females. The great length of the TH sensillum is an infrequent characteristic within Triatominae. The results show that phenetic distances between sexes are greater than between the two species. Similarity between the Mepraia species and T. eratyrusiformis was found as they all show long bristles (BR) and TH and two sized basiconic receptors (BA), a pattern that have not been observed in other species of Triatominae. These characters are not present in T. breyeri.

Genomic changes of Chagas disease vector, South America

We analyzed the main karyologic changes that have occurred during the dispersion of Triatoma infestans, the main vector of Chagas disease. We identified two allopatric groups, named Andean and non-Andean. The Andean specimens present C-heterochromatic blocks in most of their 22 chromosomes, whereas non-Andean specimens have only 4–7 autosomes with C-banding. These heterochromatin differences are the likely cause of a striking DNA content variation (approximately 30%) between Andean and non-Andean insects. Our study, together with previous historical and genetic data, suggests that T. infestans was originally a sylvatic species, with large quantities of DNA and heterochromatin, inhabiting the Andean region of Bolivia. However, the spread of domestic T. infestans throughout the non-Andean regions only involved insects with an important reduction of heterochromatin and DNA amounts. We propose that heterochromatin and DNA variation mainly reflected adaptive genomic changes that contribute to the ability of T. infestans to survive, reproduce, and disperse in different environments.

Genomic changes of Chagas disease vector, South America

We analyzed the main karyologic changes that have occurred during the dispersion of Triatoma infestans, the main vector of Chagas disease. We identified two allopatric groups, named Andean and non-Andean. The Andean specimens present C-heterochromatic blocks in most of their 22 chromosomes, whereas non-Andean specimens have only 4-7 autosomes with C-banding. These heterochromatin differences are the likely cause of a striking DNA content variation (approximately 30%) between Andean and non-Andean insects. Our study, together with previous historical and genetic data, suggests that T. infestans was originally a sylvatic species, with large quantities of DNA and heterochromatin, inhabiting the Andean region of Bolivia. However, the spread of domestic T. infestans throughout the non-Andean regions only involved insects with an important reduction of heterochromatin and DNA amounts. We propose that heterochromatin and DNA variation mainly reflected adaptive genomic changes that contribute to the ability of T. infestans to survive, reproduce, and disperse in different environments.

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.