Triatoma brasiliensis species complex: characterization of the external female genitalia

Characterization of External Female Genitalia in Five Triatoma Laporte Species of South America (Hemiptera: Reduviidae: Triatominae)

Currently, there are 158 valid species of triatomines, all of which are potential vectors of Trypanosoma cruzi, the etiological agent of Chagas disease. The correct taxonomic identification of triatomines is essential since each species hos a different epidemiological importance. The aim of the study is to compare five species of South American Triatoma. Here we present a comparative study of terminal abdominal segments in females by scanning electron microscopy (SEM) of the species Triatoma delpontei, T. jurbergi, T. infestans var. melanosoma, T. platensis, and T. vandae. The results showed diagnostic characters for the studied species. The dorsal view featured more valuable characters, with seven informative characters. Similarities were observed among T. delpontei, T. infestans var. melanosoma, and T. platensis, and between T. jurbergi and T. vandae, correlating with previous studies. Thus, female genital characters proved to be reliable and useful in the diagnosis of the Triatoma species studied here; additional studies, along with other sets of behavioral, morphological, and molecular data, helped to reinforce the hypotheses found here.

New in morphometry: Geometric morphometry of the external female genitalia of Triatominae (Hemiptera: Reduviidae)

The study of geometric morphometry has an impact on Triatominae studies. Currently, several taxonomic and systematic studies use this approach. The Triatominae subfamily comprises three fossil species and 154 extant species potentially capable of transmitting Trypanosoma cruzi, the causative agent of Chagas disease. This study aims to evaluate the external female genitalia of adult triatomines using multivariate geometric morphometric approaches, not only for validation but also for systematic inferences. Specimens belonging to the genera Panstrongylus, Psammolestes, Rhodnius, and Triatoma were evaluated, in addition to two species previously included in Triatoma: T. longipennis and T. phyllosoma. The results show that the external female genitalia have operational morphology and allow characterization of the species and the genera of the Triatominae. In addition, the multivariate technique enabled delimitation of the phylogenetic relationships of the subfamily, presenting results consistent with systematic studies. It can be concluded that the external female genitalia evaluated by geometric morphometry is a useful character for the taxonomy and systematics of Triatominae.

A review of the taxonomy and biology of Triatominae subspecies (Hemiptera: Reduviidae)

Due to its public health importance, as vectors of Chagas disease, the subfamily Triatominae, has received the attention of taxonomists. Knowing how to correctly identify these insects is of paramount importance for the surveillance and control of these vectors. Over many years, more than 40 triatomine subspecies were proposed. Infraspecific taxa are accepted as real entities in nature and recognized as biologically significant. Infraspecific diversity and population subdivision are frequently confused with the underlying mechanisms that lead to the formation of new species and species-level diversity. The distinction between infraspecific and interspecific divergence processes has received far less attention than species delimitation. In this work, new literature data on subspecies included in the subfamily Triatominae are presented. Data were compiled about Triatoma brasiliensis, Triatoma breyeri, Triatoma circummaculata, Triatoma dimidiata, Triatoma incrassata, Triatoma infestans, Triatoma phyllosoma, Triatoma protracta, Triatoma recurva, Triatoma rubida, Triatoma sanguisuga, Triatoma vitticeps, Panstrongylus megistus, Paratriatoma hirsuta, and Paratriatoma lecticularia subspecies. Although several of these subspecies have been synonymized, herein, we emphasize that some subspecies may be valid. Therefore, further studies are needed on the taxonomy, evolution, phylogeny, biogeography, ecology, physiology, and behavior of species to reinforce, or to invalidate the infraspecific status in the subfamily.

Monitoring Rhodnius neglectus (Lent, 1954) populations’ susceptibility to insecticide used in controlling actions in urban areas northwest of São Paulo state

Background:

Chagas disease (CD) is caused by the flagellate protozoan Trypanosoma cruzi and can be carried by different species of triatomines, including Rhodnius neglectus, which is wild, well distributed in Brazil, and has formed colonies in palm trees located in urban areas of municipalities in the state of São Paulo. Chemical control has been routinely used to reduce population density, but each year, there has been an increase in species dispersion and density. This study aimed to evaluate the susceptibility of insects to insecticides used in control.

Methods:

The reference population was collected from Araçatuba municipality, Nilce Maia. Dilutions of deltamethrin were prepared and applied to the back of the first-stage nymphs, which were biologically synchronized. The control group received pure acetone only. Mortality was assessed after 72 h.

Results:

The mortality rate with respect to diagnostic dose was 100%. The susceptibility profile observed for this population showed RR₅₀ ranging from 1.76 to 3.632.

Conclusions:

The populations were susceptible to the insecticides tested. It is possible that the insecticide residual effect on this ecotope has decreased the lifespan, and controlling failures may be the cause of recolonization in this environment.

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.

Revisiting the Hybridization Processes in the Triatoma brasiliensis Complex (Hemiptera, Triatominae): Reproductive Isolation between Triatoma petrocchiae and T. b. brasiliensis and T. lenti

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 triatomine species is essential for vector control programs. In general, triatomines are identified by external morphological characters. However, some species are very similar or even morphologically identical, making the use of complementary analyses for the correct identification of species important. For this reason, this study focused on the use of experimental crosses to assess the specific status of species of the Triatoma brasiliensis species complex. The crosses did not result in hybrids, demonstrating that there are pre-zygotic reproductive barriers installed between T. petrocchiae and the other species of the T. brasiliensis complex (which confirms the specific status of the species according to the biological species concept). On the basis of the results above, we demonstrated that T. petrocchiae is reproductively isolated from T. b. brasiliensis and T. lenti. Furthermore, we suggest that T. petrocchiae is the species most derived from the T. brasiliensis complex.

Abstract

Triatoma petrocchiae is a species morphologically similar to T. b. brasiliensis (which resulted in a synonymization event); despite this similarity, genetic, morphological, and experimental crossbreeding studies confirmed the specific status of T. petrocchiae. Considering that both species have been reported living in sympatry and that, for a long time, most species of the T. brasiliensis complex were considered only chromatic variants of T. b. brasiliensis, we carried out experimental crosses between T. b. brasiliensis and T. petrocchiae (to confirm whether these species are reproductively isolated) and between T. lenti and T. petrocchiae (to assess whether T. petrocchiae also presents prezygotic isolation with the other species of the T. brasiliensis complex). Reciprocal experimental crosses were conducted, and weekly, the eggs were collected, counted, and separated in new containers to assess the hatch rate. Neither cross resulted in hybrids, demonstrating that there are pre-zygotic reproductive barriers installed between T. petrocchiae and the other species of the T. brasiliensis complex. On the basis of the results above, we demonstrated that T. petrocchiae is reproductively isolated from T. b. brasiliensis and T. lenti. Furthermore, we suggest that T. petrocchiae is the species most derived from the T. brasiliensis complex.

Revisiting the hybridization processes in the Triatoma brasiliensis complex (Hemiptera, Triatominae): Interspecific genomic compatibility point to a possible recent diversification of the species grouped in this monophyletic complex

Triatomines are hematophagous insects of great epidemiological importance, since they are vectors of the protozoan Trypanosoma cruzi, the etiological agent of Chagas disease. Triatoma brasiliensis complex is a monophyletic group formed by two subspecies and six species: T. b. brasiliensis, T. b. macromelasoma, T. bahiensis, T. juazeirensis, T. lenti, T. melanica, T. petrocchiae and T. sherlocki. The specific status of several species grouped in the T. brasiliensis complex was confirmed from experimental crossing and analysis of reproductive barriers. Thus, we perform interspecific experimental crosses between T. lenti and other species and subspecies of the T. brasiliensis complex and perform morphological analysis of the gonads and cytogenetic analysis in the homeologous chromosomes of the hybrids of first generation (F1). Besides that, we rescue all the literature data associated with the study of reproductive barriers in this monophyletic complex of species and subspecies. For all crosses performed between T. b. brasiliensis, T. b. macromelasoma, T. juazeirensis and T. melanica with T. lenti, interspecific copulas occurred (showing absence of mechanical isolation), hybrids were obtained, none of the male hybrids presented the phenomenon of gonadal dysgenesis and 100% pairing between the chromosomes homeologous of the hybrids was observed. Thus, we demonstrate that there are no pre-zygotic reproductive barriers installed between T. lenti and the species and subspecies of the T. brasiliensis complex. In addition, we demonstrate that the hybrids obtained between these crosses have high genomic compatibility and the absence of gonadal dysgenesis. These results point to reproductive compatibility between T. lenti and species and subspecies of the T. brasiliensis complex (confirming its inclusion in the complex) and lead us to suggest a possible recent diversification of the taxa of this monophyletic group.

Characterization of Female External Genitalia and Eggs of Four South American Species of the Triatoma Laporte, 1832 Genus (Hemiptera: Reduviidae: Triatominae)

Simple Summary

We present a morphological and morphometric study with T. garciabesi, T. guasayana, T. patagonica, and T. sordida sensu stricto species within the Triatoma genus. This group of species is important for the eco-epidemic scenario of Chagas disease in the Americas; their species have morphological, biological, and behavioral similarities that make diagnosis difficult. For the first time, the description of the female external genitalia by scanning electron microscopy (SEM), a character that has helped with the delimitation of species and genera in Triatominae, is published, in addition to presenting an extensive study with eggs, covering morphology and morphometry. The study with eggs is an important tool in taxonomic studies of the subfamily. In addition to taxonomic contributions, it was possible through the descriptions to corroborate the validity of T. garciabesi and confirm the current classification of these species.

Abstract

Triatoma is the most diversified and one of the most important genera from an epidemiological perspective. Given the difficulty in identifying some species of the Triatoma genus, morphological, histological, and morphometric studies were performed to provide new characters that make it possible to differentiate T. garciabesi, T. guasayana, T. patagonica, and T. sordida sensu stricto, triatomines that overlap geographically and have vector potential. Through the external female genitalia, as well as morphology, morphometry, and histology of eggshells, it was possible to discriminate the four species. In addition, this study reinforces the taxonomic validity of T. garciabesi and provides new data for discussion on systematic issues of T. guasayana and T. patagonica.

Colonization by Panstrongylus megistus (Hemiptera, Reduviidae, Triatominae) in an urban park in the city of São Paulo

INTRODUCTION:

This communication reports on the occurrence of colonization by Panstrongylus megistus in an urban park in the municipality of São Paulo, Brazil.

METHODS:

Entomological research includes active search for vectors based on notifications by the population and identification and examination of insects.

RESULTS:

A colony of triatomines was found to be associated with enclosed birds.

CONCLUSIONS:

The occurrence of P. megistus has already been reported in the city of São Paulo; however, reports of colonization by this species provide evidence of its potential for the occupation of artificial ecotopes, which may pose a risk to the human population.

External female genitalia of Triatoma jatai, Triatoma costalimai and Triatoma williami (Hemiptera: Reduviidae: Triatominae)

Background

Taxonomic identification of triatomines is generally performed based on aspects of their external morphology. However, the use of a multidisciplinary approach, considering morphological aspects of the external genitalia, morphometry, genetics, and phylogeography has been suggested, especially for similar and/or cryptic species. The rupestral species Triatoma jatai Gonçalves et al., 2013, Triatoma costalimai Verano & Galvão, 1959 and Triatoma williami Galvão et al., 1965, which are morphologically similar, have been found naturally infected with Trypanosoma cruzi (Chagas, 1909) in wild, peridomestic, and intradomestic environments, representing a risk of new outbreaks of Chagas disease. This study presents morphological description complementation of these species, with an emphasis on the structures of the female external genitalia, using scanning electron microscopy.

Methods

The females of T. jatai and T. costalimai (n = 10 of each) were captured in the Brazilian municipalities of Paranã and Aurora do Tocantins and were identified with the use of a dichotomous key for the Matogrossensis subcomplex. Females of T. williami (n = 5), were obtained from a laboratory colony. The females were cut transversely at the sixth abdominal segment and examined under scanning electron microscopy (SEM) at the Oswaldo Cruz/Fiocruz Institute Electronic Microscopy Platform.

Results

It was possible to differentiate the three species based on the characteristics of urotergites VII, VIII and IX and urosternite VII, as well as the genital plaques, gonocoxites, and gonapophyses. To our knowledge, morphological differences in the spines present on gonapophysis 8 in triatomines are described here for the first time.

Conclusions

The results show that external genitalia of females are useful structures to differentiate T. costalimai, T. jatai and T. williami. SEM analysis contributes to and corroborates, together with other tools morphological and molecular, the distinction of the three species.