Sylvatic Ecotopes Research Articles

Phlebotomine (Diptera: Psychodidae) species and their blood meal sources in a new leishmaniasis focus in Los Montes de María, Bolívar, in northern Colombia

Introduction. El Alférez, a village in Los Montes de María (Bolívar, Colombia) and a macro-focus of leishmaniasis, recorded its first case in 2018, evidencing changes in the distribution and eco-epidemiology of the disease, although interactions between vectors and local fauna remain unknown. Objective. To evaluate the diversity of sandflies and their blood meal sources in the community of El Alférez in the municipality of El Carmen de Bolívar (Bolívar, Colombia). Materials and methods. In 2018, sandflies were collected using LED-based light traps in domestic, peridomestic, and sylvatic ecotopes and identified at the species level. Multiplex polymerase chain reaction targeting the mitochondrial cytochrome B gene was used to analyze blood from the digestive tract. Results. Lutzomyia evansi was the most abundant species (71.85%; n = 485/675), followed by Lu. panamensis, Lu. gomezi, Lu. trinidadensis, Lu. dubitans, Lu. abonnenci, and Lu.aclydifera. Twenty-five percent of the species had blood meals from Canis familiaris (36.00%; n = 9/25), Ovis aries (36.00%; n=9:/25), Bos taurus (24.00%; n = 6/25), Sus scrofa (20.00%; n = 5/25), and Homo sapiens (8.00%; n = 2/25). Lutzomyia evansi registered the highest feeding frequency (68.00%; n = 17/25), predominantly on a single (44.00%; n = 11/25) or multiple species (24.00%; n = 6/25). Conclusion. Results indicate a eclectic feeding behavior in Lu. evansi, implying potential reservoir hosts for Leishmania spp. and increasing transmission risk. This study is a first step towards understanding the diversity of mammalian blood sources used by sandflies, that may be crucial for vector identification and formulation of effective control measures.

Does Trypanosoma cruzi (Chagas, 1909) (Kinetoplastida: Trypanosomatidae) modify the antennal phenotype of Triatoma dimidiata (Latreille, 1811) (Hemiptera: Triatominae)?

BackgroundTriatoma dimidiata is a vector of the protozoan parasite Trypanosoma cruzi, the etiologic agent of Chagas disease. Phenotypic plasticity allows an organism to adjust its phenotype in response to stimuli or environmental conditions. Understanding the effect of T. cruzi on the phenotypic plasticity of its vectors, known as triatomines, has attracted great interest because of the implications of the parasite–triatomine interactions in the eco-epidemiology and transmission of the etiologic agent of Chagas disease. We investigated if the infection of the vector with T. cruzi may be associated with a change in the antennal phenotype of sylvatic, domestic, and laboratory-reared populations of T. dimidiata.MethodsThe abundance of each type of sensillum (bristles, basiconic, thick- and thin-walled trichoid) on the antennae of T.cruzi-infected and non-infected T.dimidiata reared in the laboratory or collected in sylvatic and domestic ecotopes were measured under light microscopy and compared using Kruskal–Wallis non-parametric tests and permutational multivariate analysis of variance.ResultsWe found significant differences between sensilla patterns of infected and non-infected insects within sylvatic and domestic populations. Conversely, we found no significant differences between sensilla patterns of infected and non-infected insects within the laboratory-reared population. Besides, for sylvatic and domestic populations, sexual dimorphism tended to be increased in infected insects.ConclusionThe differences observed in infected insects could be linked to higher efficiency in the perception of odor molecules related to the search for distant mates and hosts and the flight dispersal in search of new habitats. In addition, these insects could have a positive effect on population dynamics and the transmission of T.cruzi.Graphical

Enzootic Trypanosoma cruzi infection by Rhodnius prolixus shows transmission to humans and dogs in Vichada, Colombia.

Rhodnius prolixus is considered the most relevant Trypanosoma cruzi vector in Colombia and Venezuela due it is responsible for domestic transmission in both countries. However, a wild population of this species is distributed in the eastern plains of the Orinoco region and Amazonia jungle, where its epidemiological importance has not been sufficiently elucidated. This study aimed to assess epidemiological parameters of T. cruzi transmission in the Department of Vichada, Colombia. We determined the characteristics of T. cruzi transmission using entomological studies in domestic and sylvatic ecotopes. We analyzed the T. cruzi infection in triatomine insects, identified blood meal sources, and conducted a serological determination of T. cruzi infection in scholar-aged children, domestic dogs, and wild hosts. Fifty-four triatomine bugs, 40 T. maculata and 14 R. prolixus were collected in peridomestic and sylvatic ecotopes. Infected R. prolixus was observed in La Primavera, Santa Rosalia, and Cumaribo municipalities. All the T. maculata bugs were not infected. Serological analysis indicated that two of 3,425 children were T. cruzi positive. The seroprevalence in domestic dogs was 10,5% (49/465). Moreover, 22 synanthropic mammals were sampled, being Didelphis marsupialis the most common. TcI genotype was detected in seropositive dogs, R. prolixus, and D. marsupialis. The present work describes extra domestic R. prolixus and D. marsupialis in a sylvatic T. cruzi transmission cycle with transmission to humans and domestic dogs in Colombia's Vichada Department.

The connection between Trypanosoma cruzi transmission cycles by Triatoma brasiliensis brasiliensis: A threat to human health in an area susceptible to desertification in the Seridó, Rio Grande do Norte, Brazil.

An outbreak of Chagas disease, possibly involving its vector Triatoma brasiliensis brasiliensis, was identified in the state of Rio Grande do Norte (RN). Given the historical significance of this vector in public health, the study aimed to evaluate its role in the transmission dynamics of the protozoan Trypanosoma cruzi in an area undergoing desertification in the Seridó region, RN, Brazil. We captured triatomines in sylvatic and anthropic ecotopes. Natural vector infection was determined using parasitological and molecular methods and we identified discrete typing units (DTUs) of T. cruzi by analyzing the COII gene of mtDNA, 24Sα rDNA, and mini-exon gene. Their blood meals sources were identified by amplification and sequencing of the mtDNA cytochrome b gene. A total of 952 T. b. brasiliensis were captured in peridomestic (69.9%) and sylvatic ecotopes (30.4%). A wide range of natural infection rates were observed in peridomestic (36.0% - 71.1%) and sylvatic populations (28.6% - 100.0%). We observed the circulation of TcI and TcII DTUs with a predominance of Tcl in sylvatic and peridomestic environments. Kerodon rupestris, rocky cavy (13/39), Homo sapiens, human (8/39), and Bos taurus, ox (6/39) were the most frequently detected blood meals sources. Thus, Triatoma b. brasiliensis is invading and colonizing the human dwellings. Furthermore, high levels of natural infection, coupled with the detection of TcI and TcII DTUs, and also the detection of K. rupestris and H. sapiens as blood meals sources of infected T. b. brasiliensis indicate a risk of T. cruzi transmission to human populations in areas undergoing desertification.

Genotypic Trypanosoma cruzi distribution and parasite load differ ecotypically and according to parasite genotypes in Triatoma brasiliensis from endemic and outbreak areas in Northeastern Brazil

This study aimed to identify the Trypanosoma cruzi genotypes and their relationship with parasitic load in distinct geographic and ecotypic populations of Triatoma brasiliensis in two sites, including one where a Chagas disease (ChD) outbreak occurred in Rio Grande do Norte state, Brazil. Triatomine captures were performed in peridomestic and sylvatic ecotopes in two municipalities: Marcelino Vieira – affected by the outbreak; and Currais Novos – where high pressure of peridomestic triatomine infestation after insecticide spraying have been reported. The kDNA-PCR was used to select 124 T. cruzi positive triatomine samples, of which 117 were successfully genotyped by fluorescent fragment length barcoding (FFLB). Moreover, the T. cruzi load quantification was performed using a multiplex TaqMan qPCR. Our findings showed a clear ecotypic segregation between TcI and TcII harboured by T. brasiliensis (p<0.001). Although no genotypes were ecotypically exclusive, TcI was predominant in peridomestic ecotopes (86%). In general, T. brasiliensis from Rio Grande do Norte had a higher T. cruzi load varying from 3.94 to 7.66 x 106T. cruzi per insect. Additionally, TcII (median value=299,504 T. cruzi/intestine unit equivalents) had more than twice (p=0.1) the parasite load of TcI (median value=149,077 T. cruzi/intestine unit equivalents), which can be attributed to a more ancient co-evolution with T. brasiliensis. The higher prevalence of TcII in the sylvatic T. brasiliensis (70%) could be associated with a more diversified source of bloodmeals for wild insect populations. Either TcI or TcII may have been responsible for the ChD outbreak that occurred in the city of Marcelino Vieira. On the other hand, a smaller portion of T. brasiliensis was infected by TcIII (3%) in the peridomicile, in addition to T. rangeli genotype A (1%), often found in mixed infections. Our results highlight the need of understanding the patterns of T. cruzi genotype´s development and circulation in insect vectors and reservoirs as a mode of tracking situations of epidemiologic importance, as the ChD outbreak recently recorded for Northeastern Brazil.

First genotyping of Trypanosoma cruzi from naturally infected Triatoma juazeirensis, Triatoma melanica and Triatoma sherlocki from Bahia State, Brazil.

Many previous studies have shown a great phylogenetic and biological variability of Trypanosoma cruzi using different molecular and biochemical methods. Populations of T. cruzi were initially clustered into two main lineages called TcI and TcII by the size of the mini-exon PCR product. In the present study, 33 isolates derived from three triatomine taxa, which belong to the Triatoma brasiliensis species complex (Triatoma juazeirensis, Triatoma melanica and Triatoma sherlocki); collected in three distinct areas of Bahia state were characterized by PCR. The isolates were identified by the size of the mini-exon gene, 18S rRNA and 24Sα rRNA amplicons. T. cruzi isolates obtained in sylvatic and intradomiciliar ecotopes, derived from T. juazeirensis and T. melanica, were identified as TcI while the parasites originated from T. sherlocki were characterized as TcI and TcII genotypes, respectively. Those species are present in sylvatic ecotopes but are able to infest intradomiciliar areas. Therefore, it would be important to maintain studies in those localities of Bahia and further investigate the possibilities of Chagas disease transmission. Human disease may occur by any T. cruzi genotype and not only by TcII as it is the case in Amazonia.

Disentangling Trypanosoma cruzi transmission cycle dynamics through the identification of blood meal sources of natural populations of Triatoma dimidiata in Yucat\xe1n, Mexico

BackgroundIn the Yucatán Peninsula, Mexico, Triatoma dimidiata is the main vector of Trypanosoma cruzi, the causative agent of Chagas disease. Little effort has been made to identify blood meal sources of T. dimidiata in natural conditions in this region, although this provides key information to disentangle T. cruzi transmission cycles and dynamics and guide the development of more effective control strategies. We identified the blood meals of a large sample of T. dimidiata bugs collected in different ecotopes simultaneously with the assessment of bug infection with T. cruzi, to disentangle the dynamics of T. cruzi transmission in the region.MethodsA sample of 248 T. dimidiata bugs collected in three rural villages and in the sylvatic habitat surrounding these villages was used. DNA from each bug midgut was extracted and bug infection with T. cruzi was assessed by PCR. For blood meal identification, we used a molecular assay based on cloning and sequencing following PCR amplification with vertebrate universal primers, and allowing the detection of multiple blood meals in a single bug.ResultsOverall, 28.7% of the bugs were infected with T. cruzi, with no statistical difference between bugs from the villages or from sylvatic ecotopes. Sixteen vertebrate species including domestic, synanthropic and sylvatic animals, were identified as blood meal sources for T. dimidiata. Human, dog and cow were the three main species identified, in bugs collected in the villages as well as in sylvatic ecotopes. Importantly, dog was highlighted as the main blood meal source after human. Dog was also the most frequently identified animal together with human within single bugs, and tended to be associated with the infection of the bugs.ConclusionsDog, human and cow were identified as the main mammals involved in the connection of sylvatic and domestic transmission cycles in the Yucatán Peninsula, Mexico. Dog appeared as the most important animal in the transmission pathway of T. cruzi to humans, but other domestic and synanthropic animals, which most were previously reported as important hosts of T. cruzi in the region, were evidenced and should be taken into account as part of integrated control strategies aimed at disrupting parasite transmission.

Influence of mating and feeding on reproduction pattern of haematophagous bug Triatoma williami Galvão, Souza &amp; Lima, 1965 (Hemiptera, Triatominae)

Abstract The bloodsucking bug Triatoma williami is the main vector of Trypanosoma cruzi, the etiological agent of Chagas disease in State of Mato Grosso, Brazil. It occurs in sylvatic areas of Brazilian savanna with often records of adult specimens in domestic and peridomestic habitats. We describe, for the first time, the reproductive parameters of T. williami females such as fecundity, fertility and lifespan. We also evaluate whether mating and nourishment status of females of T. williami may modulate the reproductive parameters. As a result, the presence of male corroborated to increase female lifespan from 5.14±1,77 to 34.57±10,86 weeks. The oviposition rate in mated female increased 275% when we compared to the fecundity values in unmated females. Finally, our results indicate that mating is crucial to improve lifespan and fecundity of T. williami females. This characteristic may be related to the environmental conditions under T. williami develops, because the sylvatic ecotopes form small scattered colonies with infrequent access to blood sources.

Uncovering vector, parasite, blood meal and microbiome patterns from mixed-DNA specimens of the Chagas disease vector Triatoma dimidiata.

Chagas disease, considered a neglected disease by the World Health Organization, is caused by the protozoan parasite Trypanosoma cruzi, and transmitted by >140 triatomine species across the Americas. In Central America, the main vector is Triatoma dimidiata, an opportunistic blood meal feeder inhabiting both domestic and sylvatic ecotopes. Given the diversity of interacting biological agents involved in the epidemiology of Chagas disease, having simultaneous information on the dynamics of the parasite, vector, the gut microbiome of the vector, and the blood meal source would facilitate identifying key biotic factors associated with the risk of T. cruzi transmission. In this study, we developed a RADseq-based analysis pipeline to study mixed-species DNA extracted from T. dimidiata abdomens. To evaluate the efficacy of the method across spatial scales, we used a nested spatial sampling design that spanned from individual villages within Guatemala to major biogeographic regions of Central America. Information from each biotic source was distinguished with bioinformatics tools and used to evaluate the prevalence of T. cruzi infection and predominant Discrete Typing Units (DTUs) in the region, the population genetic structure of T. dimidiata, gut microbial diversity, and the blood meal history. An average of 3.25 million reads per specimen were obtained, with approximately 1% assigned to the parasite, 20% to the vector, 11% to bacteria, and 4% to putative blood meals. Using a total of 6,405 T. cruzi SNPs, we detected nine infected vectors harboring two distinct DTUs: TcI and a second unidentified strain, possibly TcIV. Vector specimens were sufficiently variable for population genomic analyses, with a total of 25,710 T. dimidiata SNPs across all samples that were sufficient to detect geographic genetic structure at both local and regional scales. We observed a diverse microbiotic community, with significantly higher bacterial species richness in infected T. dimidiata abdomens than those that were not infected. Unifrac analysis suggests a common assemblage of bacteria associated with infection, which co-occurs with the typical gut microbial community derived from the local environment. We identified vertebrate blood meals from five T. dimidiata abdomens, including chicken, dog, duck and human; however, additional detection methods would be necessary to confidently identify blood meal sources from most specimens. Overall, our study shows this method is effective for simultaneously generating genetic data on vectors and their associated parasites, along with ecological information on feeding patterns and microbial interactions that may be followed up with complementary approaches such as PCR-based parasite detection, 18S eukaryotic and 16S bacterial barcoding.

Ongoing quiescence in the Borborema Plateau Plague focus (Paraiba, Brazil).

Plague is a zoonosis caused by Yersinia pestis, whose cycle is based on a reservoir system composed of mammals and their fleas. Its transmission cycle presents long enzootic periods with undetected cases, sometimes misleading that the cycle is extinct. While surveillance activities in Brazil are being carried out only in some focal areas, the serologic results confirm the persistence of Y. pestis in all monitored areas. We studied the small mammal assembly and Y. pestis presencein the Borborema Plateau Focus within the state of Paraíba, which staged the last Brazilian plague outbreak (1986-1987), through aninventory and Y. pestis detection survey of small mammals in peridomestic and sylvatic areas from two municipalities in the state of Paraíba.The field sampling captured 45 specimens (27 marsupials, 18 rodents), of 10 species. Only two species (one marsupial, one rodent) were captured in both peridomestic and sylvatic ecotopes. The sylvatic ecotope had higher richness and abundance. No evidence of circulation of the pathogen was detected, however, this result does not discard the necessity of continuous epidemiological surveillance due to the risk of rekindling the foci after long dormant periods, especially given the current epidemiological transition occurring on a Global scale.

Environmental Determinants of the Distribution of Chagas Disease Vector Triatoma dimidiata in Colombia.

Triatoma dimidiata (Hemiptera: Reduviidae) is a secondary vector of Trypanosoma cruzi in Colombia and represents an important epidemiological risk mainly in the central and oriental regions of the country where it occupies sylvatic, peridomestic, and intradomestic ecotopes, and because of this complex distribution, its distribution and abundance could be conditioned by environmental factors. In this work, we explored the relationship between T. dimidiata distribution and environmental factors in the northwest, northeast, and central zones of Colombia and developed predictive models of infestation in the country. The associations between the presence ofT. dimidiata and environmental variables were studied using logistic regression models and ecological niche modeling for a sample of villages in Colombia. The analysis was based on the information collected in field about the presence ofT. dimidiata and the environmental data for each village extracted from remote sensing images. The presence of Triatoma dimidiata(Latreille, 1811) was found to be significantly associated with the maximum vegetation index, minimum land surface temperature (LST), and the digital elevation for the statistical model. Temperature seasonality, annual precipitation, and vegetation index were the variables that most influenced the ecological niche model ofT. dimidiata distribution. The logistic regression model showed a good fit and predicted suitable habitats in the Andean and Caribbean regions, which agrees with the known distribution of the species, but predicted suitable habitats in the Pacific and Orinoco regions proposing new areas of research. Improved models to predict suitable habitats forT. dimidiata hold promise for spatial targeting of integrated vector management.

Geographic Distribution and Ecology ofTriatoma dimidiata(Hemiptera: Reduviidae) in Colombia

Triatoma dimidiata Latreille is the second most important vector of Chagas' disease in Colombia and is found in urban and periurban areas. From January 2007 to June 2008, we performed field work in 8 departments, 18 municipalities, and 44 rural villages, covering most of its known distribution and all of its ecological zones in the country. The goal was to determine the geographical distribution, the ecology, and house infestation indices of T. dimidiata over its range and hence the Chagas' disease transmission risk. In Colombia, T. dimidiata occupies a wide variety of ecosystems, from transformed ecosystems in the Andean biome with shrub and xerofitic vegetation to very dense forests in the humid tropical forests in the Sierra Nevada of Santa Marta. According to genetic and ecological criteria, at least two T. dimidiata forms of this species are present: populations from the northwest of the country (Caribbean plains) are restricted to palm tree habitats, and domestic involvement is limited to sporadic visits because of attraction by light; and populations of the east region (Andean mountains) presenting a complex distributional pattern including sylvatic, peridomestic, and domiciliated ecotopes, and occupying a great variety of life zones. The latter population is of epidemiological importance due to the demonstrated migration and genetical flow of individuals among the different habitats. Control, therefore, must take into account its diversity of habitats.

Ecotope effect in Triatoma brasiliensis (Hemiptera: Reduviidae) suggests phenotypic plasticity rather than adaptation

Triatoma brasiliensis (Hemiptera: Reduviidae) is an important vector of Chagas' disease in both sylvatic and peridomestic ecotopes. Discriminating between these populations of Triatominae has been proposed as a means of investigating re-infestation rates of human dwellings. Geometric morphometrics have been widely applied in the study of Triatominae polymorphisms at species and population levels. This study characterizes morphometric differences between sylvatic and peridomestic populations, as well as between sexes in T. brasiliensis specimens from Jaguaruana, Ceará, in northeastern Brazil. No differences in either the shape or size of the cephalic capsule were apparent between sexes or ecotopes. However, the wings showed differentiation in shape and size. Sexual dimorphism was detected, with females presenting significantly higher values and conformations. Size differentiation was also evident, with sylvatic specimens being generally larger than peridomestic examples. These results indicate that differences in the wings of T. brasiliensis may be related to the existence of phenotypic plasticity, and variations in size and shape may be associated with different ecotopes, possibly as a result of conditions in each micro-habitat, such as temperature, relative humidity, food supply and density.

Cholinesterase activity during embryonic development in the blood-feeding bug Triatoma patagonica

Triatoma patagonica Del Ponte (Hemiptera: Reduviidae), a vector of Chagas' disease, is widely distributed in Argentina and is found in sylvatic and peridomiciliary ecotopes, as well as occasionally in human dwellings after the chemical control of Triatoma infestans. Anti-cholinesteratic products can be applied in peridomiciliary areas and thus knowledge of cholinesterase activity during embryonic development in this species might contribute further information relevant to effective chemical control. Cholinesterase activity was characterized by reactions to eserine 10(-5) m, to increasing concentrations of substrate and to varying centrifugal speeds. Acetylcholinesterase activity was detected on day 4 and was significant from day 5. A reduction in cholinesterase activity towards acetylthiocholine (ATC) was observed on days 9 and 10 of development. Cholinesterase activity towards ATC and butyrylthiocholine (BTC) in homogenates of eggs was inhibited by eserine 10(-5) m. The shape of the curve indicating levels of inhibition at different concentrations of ATC was typical of acetylcholinesterase. Activity towards BTC did not appear to be inhibited by excess substrate, which parallels the behaviour of butyrylcholinesterases. Cholinesterase activity towards ATC was reduced in supernatant centrifuged at 15 000 g compared with supernatant centrifuged at 1100 g. The cholinesterase system that hydrolyzes mainly ATC seems to belong to the nervous system, as indicated by its behaviour towards the substrates assayed, its greater insolubility and the fact that it evolves parallel to the development of the nervous system. Knowledge of biochemical changes associated with the development and maturation of the nervous system during embryonic development would contribute to the better understanding of anti-cholinesteratic compounds with ovicidal action that might be used in control campaigns against vectors of Chagas' disease.

Sylvatic and peridomestic populations of Triatoma pseudomaculata are not significantly structured by habitat, as revealed by two genetic markers

Chagas disease remains a public health concern in Brazil and other Latin American countries, mainly due to the potential domiciliation of native triatomine species. We analyzed the genetic variability of Triatoma pseudomaculata in sylvatic and peridomestic ecotopes throughout three localities in the northeastern state of Bahia, Brazil. We studied polymorphisms generated by random amplified polymorphic DNA (RAPD) and isoenzyme electrophoresis analyses. Based on RAPD analysis, each specimen was assigned to one of three genetic clusters. Although all sylvatic specimens from one locality were grouped into the same cluster, sylvatic and peridomestic specimens from the other two localities were broadly distributed between the remaining two clusters, suggesting that geographic population structuring was not occurring. Furthermore, isoenzyme analysis suggested that distinct populations were in Hardy-Weinberg equilibrium. Low statistical values for Wright's Fst index also supported the absence of population structuring and suggested the occurrence of panmixia. We conclude that genetic flow occurs between sylvatic and peridomestic T. pseudomaculata populations, probably as a consequence of passive and active dispersion of the insects, associated with deforestation and anthropic transformations.

Molecular evidence of intraspecific variability in different habitat-related populations of Triatoma dimidiata (Hemiptera: Reduviidae) from Costa Rica

Intraspecific genetic variation among Triatoma dimidiata (Hemiptera: Reduviidae) from seven Costa Rican populations and from different domestic, peridomestic, and sylvatic ecotopes were analyzed. The complete nucleotide sequence of the nuclear ribosomal DNA internal transcribed spacer (ITS-2) and partial sequences of the cytochrome B (Cyt b) gene and the large ribosomal subunit RNA (16S) of mitochondrial DNA (mtDNA) were analyzed and compared. All ITS-2 sequences analyzed were identical and correspond to the haplotype T.dim-H1, the most common haplotype in Central American populations. Sequences of mtDNA revealed a 10.17% of polymorphism in Cyt b and 2.39% in 16S, suggesting that the Cyt b fragment is a useful marker to describe the genetic structure of populations, even at habitat-related level. The analyses of the 18 new combined T. dimidiata haplotypes (Cytb/16S/ITS-2) showed that the two main geographical locations and populations studied are genetically structured showing different haplotype profiling. Only one combined haplotype was shared in the studied areas (Cytb.d/16S.a). Seven haplotypes exclusive for domestic/peridomestic populations, five for sylvatic, and six shared haplotypes for both habitat-related ecotopes are described. Although the relationship between the habitat and the haplotype profiling is less clear, there are different patterns of haplotype distribution in each geographic area between the two habitat-related ecotopes studied (domestic/peridomestic and sylvatic), some of them reflected in the phylogenetic relationships analyzed. The intraspecific variability detected may underlie the known plasticity of T. dimidiata, an important vector for Chagas disease transmission, suggesting that this species must be continuously monitored.

Presence ofRhodnius ecuadoriensisin Sylvatic Habitats in the Southern Highlands (Loja Province) of Ecuador

The main vectors of Chagas disease in Ecuador are Triatoma dimidiata and Rhodnius ecuadoriensis. The latter species occupies domestic and peridomestic habitats, as well as sylvatic ecotopes--particularly associated with Phytelephas aequatorialis palm trees--in the western coastal region of Ecuador. In the southern highlands, however, such palm tree habitats are uncommon, and sylvatic populations of R. ecuadoriensis have not previously been reported to date. This study was carried out in five rural communities in Loja Province in southern Ecuador, where manual triatomine searches were conducted in various sylvatic habitats. A total of 81 squirrel nests (Sciurus stramineus) and > 200 bird nests and other habitats were searched. One hundred three R. ecuadoriensis individuals were found in 11 squirrel nests (infestation index = 13.6%, density = 2 bugs per nest searched, crowding = 9.5 bugs per infested nest, colonization index = 72.7% of infested nests with nymphs). No triatomines were found in bird nests or other sylvatic habitats. The presence of sylvatic R. ecuadoriensis in the southern highlands of Ecuador has important implications for the long-term control of Chagas disease in the region because of the possibility of reinfestation of dwellings after insecticide-based control interventions.

Reassessing the entomological investigation around the first autochthonous case of Chagas disease in Western Brazilian Amazon

In 1979, the first autochthonous case of Chagas disease in the Western Brazilian Amazon was reported and an entomological survey was carried out around it. Specimens of Rhodnius pictipes and Rhodnius robustus were collected in intradomicile and sylvatic ecotopes. Adult bugs were infected with trypanosomatids. Invasion of houses by triatomines was demonstrated and the presence of infected bugs inside dwellings was associated with the possibility of vector-borne Chagas disease. Continuous entomological surveillance employing additional taxonomic tools is needed in the Brazilian Amazon in order to better understand the dynamics of house invasion by sylvatic triatomines and the risk of Trypanosoma cruzi infection transmission.

Development of a geographical distribution model of Rhodnius pallescens Barber, 1932 using environmental data recorded by remote sensing

Rhodnius pallescens, main vector of Trypanosoma cruzi in Panama and secondary vector in Colombia, Costa Rica and Nicaragua, represents an important epidemiological risk in those countries. It occupies sylvatic ecotopes, and because of this its distribution and abundance could be conditioned by environmental factors. In this work, we integrated environmental variables recorded by remote sensing and data of R. pallescens presence in the countries mentioned above in order to know the environmental variables with better capacity to describe the insects’ distribution, which will help to entomological surveillance and control. Standard discriminant analysis (DA) was used to determine if there is a significant difference in the environmental variation between the presence and the absence sites of R. pallescens. Forward stepwise discriminant analysis (fDA) was used to determine the environmental variables which better discriminated between presence and absence sites, and to construct a predictive map of geographical distribution. Univariate analyses were used to determine the discriminatory power of individual variables. The model derived from DA showed 89% of sensitivity and 92.8% of specificity. Multivariate and univariate analyses showed the vapor pressure deficit minimum as the principal variable among the nine most important to describe the distribution of the species, which is in agreement with the R. pallescens stenohydric status. Map shows insects’ distribution predicted by environmental variables, and moreover includes the distribution of most species belonging to Rhodnius genus, except R. domesticus, R. nasutus and R. neglectus. We interpreted these results as a reflection of the common evolution of the most Rhodnius species, except for the last ones that probably evolved isolated due to particular environmental conditions. In conclusion, this study showed that a reduced number of environmental variables can predict the distribution of R. pallescens and related species. This methodology can be very useful to make critical decisions for vectorial surveillance and control of Chagas disease vectors.

Growth changes in Rhodnius pallescens under simulated domestic and sylvatic conditions

Rhodnius pallescens Barber 1932 is a silvatic species of Triatominae living in palm trees in Colombia and part of Central America. In Colombia, the species did not adapt to domestic structures and is not considered as an important vector for humans. In Panama, Costa Rica and Nicaragua it is a recognized vector adapting to peridomestic and domestic structures.The main condition required for a Triatominae to be a significant vector of Chagas disease is its ability to colonize human dwellings. The mechanisms of this process are unknown. In this adaptation to domesticity, previous authors have reported a fairly constant reduction in general size and discussed its possible causes in terms of natural selection across various generations or of simple growth changes within one single generation. Some authors suggested that this size change could correspond to the relaxation of a selective pressure in the wild, where larger phenotypes are possibly selected due to their greater capacity to resist temporary food shortages. Others suggested that growth patterns could change quickly in domestic conditions because of faster development time or higher population density.Up to now, these hypotheses have not been explored experimentally. We built a laboratory protocol measuring the effects of population density and feeding patterns on the growth of R. pallescens. A total of 320 first instar nymphs from a 10 generations old laboratory colony were randomly subdivided into four regimes combining density and feeding frequency variation. Using geometric morphometric techniques applied to the emerging adults, we evaluated size and shape variation of the heads and the wings across the four experimental designs. The regimes tentatively paralleled changes occurring for a Triatominae in the transition from silvatic (low population density, low feeding frequency) to domestic (higher density, higher feeding frequency) habitats. Density and feeding frequency combined their effect within the span of one single generation to produce similar size changes for wings and heads, but significant only for the wings. No significant variation could be detected for shape variation, neither for the wing nor for the head.Our data suggest that selection is not needed to account for observed changes between sylvatic and domestic ecotopes, and they did not agree with an effect of development time on size. They highlighted the importance of the interaction between population density and feeding frequency to produce specific and significant variation in the insect dimensions.