Association between environmental gradient of anthropization and phenotypic plasticity in two species of triatomines.

BACKGROUND: Triatoma garciabesi and T. guasayana are considered secondary vectors of Trypanosoma cruzi and frequently invade rural houses in central Argentina. Wing and head structures determine the ability of triatomines to disperse. Environmental changes exert selective pressures on populations of both species, promoting changes in these structures that could have consequences for flight dispersal. The aim of this study was to investigate the relationship between a gradient of anthropization and phenotypic plasticity in flight-related traits. METHODS: The research was carried out in Cruz del Eje and Ischilín departments (Córdoba, Argentina) and included 423 individuals of the two species of triatomines. To measure the degree of anthropization, a thematic map was constructed using supervised classification, from which seven landscapes were selected, and nine landscape metrics were extracted and used in a hierarchical analysis. To determine the flight capacity and the invasion of dwellings at different levels of anthropization for both species, entomological indices were calculated. Digital images of the body, head and wings were used to measure linear and geometric morphometric variables related to flight dispersion. One-way ANOVA and canonical variate analysis (CVA) were used to analyze differences in size and shape between levels of anthropization. Procrustes variance of shape was calculated to analyze differences in phenotypic variation in heads and wings. RESULTS: Hierarchical analysis was used to classify the landscapes into three levels of anthropization: high, intermediate and low. The dispersal index for both species yielded similar results across the anthropization gradient. However, in less anthropized landscapes, the density index was higher for T. garciabesi. Additionally, in highly anthropized landscapes, females and males of both species exhibited reduced numbers. Regarding phenotypic changes, the size of body, head and wings of T. garciabesi captured in the most anthropized landscapes was greater than for those captured in less anthropized landscapes. No differences in body size were observed in T. guasayana collected in the different landscapes. However, males from highly anthropized landscapes had smaller heads and wings than those captured in less anthropized landscapes. Both wing and head shapes varied between less and more anthropogenic environments in both species. CONCLUSIONS: Results of the study indicate that the flight-dispersal characteristics of T. garciabesi and T. guasayana changed in response to varying degrees of anthropization.

Morphometric study of the legs of the main Chagas vector, Triatoma infestans (Hemiptera: Reduviidae).

In triatomines, vectors of Chagas disease, active dispersal takes place by walking and flying. Flight has received more attention than walking although the last is the dispersal modality used by nymphs due to their lack of wings and also used by adults, which would facilitate the colonization and reinfestation of houses after vector control actions. The present work studied the morphometrical variation of Triatoma infestans legs, the main vector of Chagas disease the Southern Cone of South America. We described morphometric traits and the natural variation of each leg segment. Different linear, size and shape variables of each component of the three right legs of fifth instar nymphs of T. infestans were analyzed using morphometric tools. We analyzed differentiation, variation and correlation for each segment across the fore-, mid and hind legs using different statistical approaches such as general linear model, canonical variates analysis, test of equality of coefficient of variation and partial least square analysis. We also analyzed variation and correlation between segments within each leg with partial least square and morphometric disparity analyses. Our results showed that the segments differed between legs, as general trends, the dimensions (length, width and/or size) were greater in the hind legs, smaller in the forelegs and intermediate in the mid ones. The femur and tibia (length and/or width) showed differences in morphometric variation between legs and the femur and tibia showed the highest levels of correlation between legs. On the other hand, in the fore- and mid legs, the femur (length or width) showed similar variation with tibia and tarsus lengths, but in the hind legs, the femur showed similar variation with all segments and not with the tibia length, and there were strong correlations between linear measurement within each leg. Our results suggest that the femur and tibia could play a determining role in the coordination between the legs that determines the walking pattern. Considering that these segments would also be linked to the specific function that each leg has, this study suggests a preponderant role of the femur and tibia in the walking locomotion of T. infestans.

Relationship between genetic diversity and morpho-functional characteristics of flight-related traits in Triatoma garciabesi (Hemiptera: Reduviidae).

BACKGROUND: Triatoma garciabesi, a potential vector of the parasitic protozoan Trypanosoma cruzi, which is the causative agent of Chagas disease, is common in peridomestic and wild environments and found throughout northwestern and central Argentina, western Paraguay and the Bolivian Chaco. Genetic differentiation of a species across its range can help to understand dispersal patterns and connectivity between habitats. Dispersal by flight is considered to be the main active dispersal strategy used by triatomines. In particular, the morphological structure of the hemelytra is associated with their function. The aim of this study was to understand how genetic diversity is structured, how morphological variation of dispersal-related traits varies with genetic diversity and how the morphological characteristics of dispersal-related traits may explain the current distribution of genetic lineages in this species. METHODS: Males from 24 populations of T. garciabesi across its distribution range were examined. The cytochrome c oxidase I gene (coI) was used for genetic diversity analyses. A geometric morphometric method based on landmarks was used for morpho-functional analysis of the hemelytra. Centroid size (CS) and shape of the forewing, and contour of both parts of the forewing, the head and the pronotum were characterised. Length and area of the forewing were measured to estimate the aspect ratio. RESULTS: The morphometric and phylogenetic analysis identified two distinct lineages, namely the Eastern and Western lineages, which coincide with different ecological regions. The Eastern lineage is found exclusively in the eastern region of Argentina (Chaco and Formosa provinces), whereas the Western lineage is prevalent in the rest of the geographical range of the species. CS, shape and aspect ratio of the hemelytra differed between lineages. The stiff portion of the forewing was more developed in the Eastern lineage. The shape of both portions of the hemelytra were significantly different between lineages, and the shape of the head and pronotum differed between lineages. CONCLUSIONS: The results provide preliminary insights into the evolution and diversification of T. garciabesi. Variation in the forewing, pronotum and head is congruent with genetic divergence. Consistent with genetic divergence, morphometry variation was clustered according to lineages, with congruent variation in the size and shape of the forewing, pronotum and head.

Population structure and migration in Triatoma infestans (Hemiptera: Reduviidae) from the Argentine Chaco: An integration of genetic and morphometric data.

Genetic and morphological structure of vector populations are useful to identify panmictic groups, reinfestation sources and minimal units for control interventions. Currently, no studies have integrated genetic and morphometric data in Triatoma infestans (Hemiptera: Reduviidae), one of the main vectors of Trypanosoma cruzi. We characterized the genetic and phenotypic structure of T. infestans at a small spatial scale (2-8 km), identified potential migrants and compared flight-related traits among genetic groups and between migrant and non-migrant insects in a well-defined area without insecticide spraying in the previous 12 years. We obtained microsatellite genotypes (N = 303), wing shape and size (N = 164) and body weight-to-length ratios (N = 188) in T. infestans from 11 houses in Pampa del Indio, Argentine Chaco. The uppermost level of genetic structuring partially agreed with the morphological groups, showing high degrees of substructuring. The genetic structure showed a clear spatial pattern around Route 3 and one genetic group overlapped with an area of persistent infestation and insecticide resistance. Females harboured more microsatellite alleles than males, which showed signs of isolation-by-distance. Wing shape discriminant analyses of genetic groups revealed low reclassification scores whereas wing size differed among genetic groups for both sexes. Potential migrants (8%) did not differ from non-migrants in sex, ecotope, wing shape and size. However, male migrants had lower W/L than non-migrants suggesting poorer nutritional state. Our findings may contribute to the understanding of population characteristics, dispersal dynamics and ongoing elimination efforts of T. infestans.

Extended stage duration and diminished fecundity in deltamethrin-resistant Triatoma infestans (Klug, 1834) of the Argentinean Chaco.

Pyrethroid-resistance is an emergent trait in populations of various insect species. For Triatoma infestans (Klug, 1834) (Heteroptera: Reduviidae), the major vector of Chagas disease in the southern part of South America, hotspot areas of pyrethroid-resistance have recently been found in the Chaco Province of Argentina. Resistant condition can reduce fitness of individuals in the absence of insecticide exposure, that is, fitness costs. We evaluated the existence of developmental and/or reproductive costs in T. infestans collected from two areas of pyrethroid-resistance in Chaco Province, Argentina. Three toxicological groups were defined from field-collected insects: susceptible (survival <20%), moderately resistant (survival between 20% and 80%) and highly resistant (survival >80%). Cohorts of the three toxicological groups were followed-up to study life cycle and reproductive parameters. Additionally, we parameterized matrix population growth models. First and IV nymphal stages of the resistant groups exhibited a longer stage duration than susceptible ones. The reproductive days and hatching success showed significant lower values revealing reproductive costs for the resistant groups. Matrix analysis showed lower population growth rates for the resistant groups. Our results support developmental and reproductive costs for pyrethroid-resistant individuals. This trait could be interpreted as lower population recovery ability for pyrethroid-resistant individuals compared to susceptible insects after alternative vector control actions.

Correction: Urban vectors of Chagas disease in the American continent: A systematic review of epidemiological surveys.

[This corrects the article DOI: 10.1371/journal.pntd.0011003.].

Phenotypic variability in traits related to flight dispersal in the wing dimorphic species Triatoma guasayana.

BACKGROUND: Triatoma guasayana is considered an emerging vector of Chagas disease in the Southern Cone of South America. The presence of a triatomine population with brachypterous individuals, in which both wings are reduced, has recently been reported for this species. The aim of the present study was to determine if flight-related traits varied across populations, if these traits could explain differences in flight capacity across populations and if flight-related traits are associated with geographic and/or climatic variation. METHODS: The study involved 66 male T. guasayana specimens from 10 triatomine populations. Digital images of wing, head and pronotum were used to estimate linear and geometric morphometric variables. Variations in size and shape were analysed using one-way analysis of variance and canonical variate analysis (CVA), respectively. Mantel tests were applied to analyse the relationship between morphometric and geographic distances, and the association between size measurements was analysed using Pearson's correlation. We explored covariation between size and shape variables using partial least square analyses (PLS). The association of geographic and climatic variables with size measurements was tested using linear regression analyses. We performed PLS analyses for shape measurements. RESULTS: Wing size differed significantly across triatomine populations. The CVA showed that wing shape of the brachypterous population is well discriminated from that of the other populations. The Mantel test showed a positive and significant association between wing shape and geographic distances. The heads of the brachypterous population were significantly larger than those of the other populations. Similar to wing shape, the head shape of the brachypterous population was well discriminated from those of the other populations. Pronotum width did not show significant differences across populations. Geographic and climatic factors were associated with size and shape of both the wing and head, but not with pronotum width. CONCLUSIONS: Most of the traits related to flight dispersal varied across populations. Wing shape and head shape were found to be better markers for differentiated morphological variation across populations. Head measurements also varied in accordance with this condition. Geographic and climatic variables were associated with most of the flight-related traits.

Urban vectors of Chagas disease in the American continent: A systematic review of epidemiological surveys.

BACKGROUND: Chagas is a complex and multidimensional socio-environmental health phenomenon, in which different components converge and interact. Historically, this disease was associated with insect vectors found in the rural environment. However, in the Americas, we are currently facing a new paradigm, in which different scenarios allow maintaining the vectorial transmission of the parasite through triatomine populations that either occasionally enter the dwellings or colonize urban environments. METHODOLOGY/PRINCIPAL FINDINGS: Records of scientific reports available in the PubMed and LILACS search engines were retrieved, using three criteria according to the main triatomine genera of epidemiological importance and to the general scientific production on Chagas disease in urban contexts. Results showed that records on the occurrence of vectors in urban dwellings began to increase in the last three decades. Results also showed that the main species of triatomines collected inside dwellings (18 in total) belong mainly to the genera Triatoma and Panstrongylus, with most species (16/18, 88.8%) infected with the parasite, and that infestation of triatomine species occurs in all types of cities (small, medium and large, including megalopolises), from Argentina to the USA. CONCLUSIONS/SIGNIFICANCE: Urban Chagas represents a new challenge that adds a different dimension to the problem of Chagas disease due to the particular characteristics of the lifestyle in urban agglomerates. The new scenario will require adaptations of the programs of control of vector to this shift from rural to urban settlements.

Sublethal effects of a pyrethroid insecticide on cuticle thickness, wing size and shape in the main vector Triatoma infestans.

Exposure to sublethal doses of insecticide may affect biological traits in triatomines. We investigated the effects of toxicological phenotype (pyrethroid resistance status) and exposure to sublethal doses of deltamethrin on two traits of Triatoma infestans Klug (Heteroptera: Reduviidae) using a phenotypic plasticity experimental design. First-instar nymphs from 14 and 10 full-sib families from pyrethroid-susceptible and pyrethroid-resistant populations, respectively, were used. For the susceptible population, we treated first instars topically with acetone (control) or deltamethrin (treatment) once. For the resistant population, instars were treated once, twice and three times as first, third or fifth-instar nymphs, respectively. We measured cuticle thickness, wing size and wing shape of 484 emerging adults, and tested for treatment effects using mixed ANOVA and MANOVA models. Toxicological phenotype, exposure to deltamethrin and full-sib family exerted significant effects on cuticle thickness, wing size and wing shape. Adult triatomines previously treated with deltamethrin developed significantly thicker cuticles than control triatomines only in the resistant population and significantly bigger wings in both populations. Mean cuticle thickness and wing size increased with increasing exposures to deltamethrin. Exposure to sublethal doses of deltamethrin generated morphological modifications that may affect insect survival and flight dispersal, and hence may have evolutionary and epidemiological consequences.

Modelling the effect of density vegetation coverage and the occurrence of peridomestic infestation by Triatoma infestans in rural houses of northwest of Córdoba, Argentina.

To better understand the dispersion strategies of Triatoma infestans (Klug) (Hemiptera: Reduviidae, Triatominae), we evaluated the spatial effect of infested peridomicile and density vegetation cover in a historically endemic area for Chagas disease. The study was conducted in rural houses of the northwest of Córdoba province, Argentine, during 2012-2013. Active search of triatomines were made in domicile and peridomicile habitats. To characterize vegetation coverage, a thematic map was obtained considering five types of vegetation cover (closed/open forest, closed/open shrubland and cultural land). From each house we extracted the area of vegetation coverage, housing density and infested peridomiciles density. We used generalized linear models to evaluate the effect of these variables on the occurrence of infested peridomicile. According to our results, the probability of a peridomicile to be infested increases by 1.34 (95%CI [0.98; 1.90]) times more when peridomicile structures are in environments with higher housing density and by 1.25 (95%CI [0.84; 1.88]) more times when houses are surrounded by open shrublands. Among the multiple ecological determinants of peridomestic infestation, the influence of vegetation cover has been poorly studied. In this study we discussed the effect of the vegetation as a potential modulator of the dispersion strategies of T. infestans.

Improved vector control of Triatoma infestans limited by emerging pyrethroid resistance across an urban-to-rural gradient in the Argentine Chaco.

BACKGROUND: The sustainable elimination of Triatoma infestans in the Gran Chaco region represents an enduring challenge. Following the limited effects of a routine pyrethroid insecticide spraying campaign conducted over 2011-2013 (first period) in Avia Terai, an endemic municipality with approximately 2300 houses, we implemented a rapid-impact intervention package to suppress house infestation across the urban-to-rural gradient over 2015-2019 (second period). Here, we assess their impacts and whether persisting infestations were associated with pyrethroid resistance. METHODS: The 2011-2013 campaign achieved a limited detection and spray coverage across settings (< 68%), more so during the surveillance phase. Following community mobilization and school-based interventions, the 2015-2019 program assessed baseline house infestation using a stratified sampling strategy; sprayed all rural houses with suspension concentrate beta-cypermethrin, and selectively sprayed infested and adjacent houses in urban and peri-urban settings; and monitored house infestation and performed selective treatments over the follow-up. RESULTS: Over the first period, house infestation returned to pre-intervention levels within 3-4 years. The adjusted relative odds of house infestation between 2011-2013 and 2015-2016 differed very little (adj. OR: 1.17, 95% CI 0.91-1.51). Over the second period, infestation decreased significantly between 0 and 1 year post-spraying (YPS) (adj. OR: 0.36, 95% CI 0.28-0.46), with heterogeneous effects across the gradient. Mean bug abundance also dropped between 0 and 1 YPS and thereafter remained stable in rural and peri-urban areas. Using multiple regression models, house infestation and bug abundance at 1 YPS were 3-4 times higher if the house had been infested before treatment, or was scored as high-risk or non-participating. No low-risk house was ever infested. Persistent foci over two successive surveys increased from 30.0 to 59.3% across the gradient. Infestation was more concentrated in peridomestic rather than domestic habitats. Discriminating-dose bioassays showed incipient or moderate pyrethroid resistance in 7% of 28 triatomine populations collected over 2015-2016 and in 83% of 52 post-spraying populations. CONCLUSIONS: The intervention package was substantially more effective than the routine insecticide spraying campaign, though the effects were lower than predicted due to unexpected incipient or moderate pyrethroid resistance. Increased awareness and diagnosis of vector control failures in the Gran Chaco, including appropriate remedial actions, are greatly needed.

Phenotypic plasticity, canalisation and developmental stability of Triatoma infestans wings: effects of a sublethal application of a pyrethroid insecticide.

BACKGROUND: Triatomine control campaigns have traditionally consisted of spraying the inside of houses with pyrethroid insecticides. However, exposure to sublethal insecticide doses after the initial application is a common occurrence and may have phenotypic consequences for survivors. Here, using Triatoma infestans (the main vector of Chagas disease in the Southern Cone of South America) as a model species, we quantified the effects of exposure to a sublethal dose of pyrethroid insecticide on wing morphology. We tested if the treatment (i) induced a plastic effect (change in the character mean); (ii) altered environmental canalisation (higher individual variation within genotypes); (iii) altered genetic canalisation (higher variation among genotypes); and (iv) altered developmental stability (higher fluctuating asymmetry [FA]). METHODS: Each of 25 full-sib families known to be susceptible to pyrethroid insecticides were split in two groups: one to be treated with a sublethal dose of deltamethrin (insecticide-treated group) and the other to be treated with pure acetone (control group). Wings of the emerging adults were used in a landmark-based geometric morphometry analysis to extract size and shape measurements. Average differences among treatments were measured. Levels of variation among families, among individuals within families and among sides within individuals were computed and compared among treatments. RESULTS: Wing size and shape were affected by a sublethal dose of deltamethrin. The treated insects had larger wings and a more variable wing size and shape than control insects. For both wing size and shape, genetic variation was higher in treated individuals. Individual variations and variations in FA were also greater in deltamethrin-treated insects than in control ones for all full-sib families; however, the patterns of shape variation associated with genetic variation, individual variation and FA were different. CONCLUSIONS: Insects exposed to a sublethal dose of deltamethrin presented larger, less symmetrical and less canalised wings. The insecticide treatment jointly impaired developmental stability and genetic and environmental canalisation. The divergent patterns of shape variation suggest that the related developmental buffering processes differed at least partially. The morphological modifications induced by a single sublethal exposure to pyrethroids early in life may impinge on subsequent flight performance and consequently affect the dynamics of house invasion and reinfestation, and the effectiveness of triatomine control operations.

Characterization of melanic and non-melanic forms in domestic and peridomestic populations of Triatoma infestans (Hemiptera: Reduviidae).

BACKGROUND: Melanic (dark) morphs have been barely reported in peridomestic and sylvatic conditions for Triatoma infestans, the most important vector of Chagas disease in the Southern Cone of South America. Adults with dark and small yellow markings on the connexivum were collected after manual searches conducted by technical personnel in 62 domiciliary units in Cruz del Eje, Córdoba Province, Argentina. The last community-wide insecticide spraying campaign before the study had been conducted three years earlier. We investigated if there was a measurable color morph variation (melanic and non-melanic) in wings and connexivum; we determined infestation, distribution of melanic and non-melanic forms, and correspondence of colorimetric variation with variations in morphology (wing size and shape and body length), development (wing fluctuating asymmetry), physiology (nutritional status) or behaviour (flight initiation). RESULTS: Forty-nine females, 54 males and 217 nymphs were collected in 24 domiciliary units. House infestation and colonization were 53% and 47%, respectively. Most of the T. infestans individuals (83.2%) were collected in chicken coops; intradomicile infestation was recorded in only one case. The chromatic cluster analysis showed two well-defined groups: melanic and non-melanic. The melanic group included 17 (35%) females and 25 (46%) males. Peridomestic infestation was lower for melanic than for non-melanic adults. Melanic morphs were collected in houses from several localities. Sexual dimorphisms were confirmed by morphometric measurements. Body length was large in melanic adults (P < 0.01 only for males). Differences between groups were significant for wing size and shape, but not for weight or weight/body length ratio. Melanic females and males showed significantly higher fluctuating asymmetry (FA) indices than their non-melanic counterparts. CONCLUSIONS: This is the second report of melanic forms of T. infestans in domestic and peridomestic habitats in the Dry Chaco region of Argentina. Although non-melanic adults exhibited a higher infestation rate, melanic adults were widespread in the area and were collected in the infested domicile and in most types of peridomestic annexes. Differences in morphometric variables between groups might be due to different ecological adaptations. The higher FA levels observed in melanic individuals suggest a higher developmental instability and a selective advantage of non-melanic individuals in domestic and peridomestic habitats.

Fluctuating asymmetry and exposure to pyrethroid insecticides in Triatoma infestans populations in northeastern Argentina.

Fluctuating asymmetry (FA), a phenotypic marker used as indicator of developmental stress or instability, is sometimes associated with insecticide application and resistance. Here we investigated the occurrence and amount of wing size and wing shape FA in Triatoma infestans females and males collected before and 4 months after a community-wide pyrethroid spraying campaign in a well-defined rural area of Pampa del Indio, Argentina. Moderate levels of pyrethroid resistance were previously confirmed for this area, and postspraying house infestation was mainly attributed to this condition. In the absence of insecticide-based selective pressures over the previous 12 years, we hypothesized that 1- if postspraying triatomines were mostly survivors to insecticide spraying (pyrethroid resistant), they would have higher levels of FA than prespraying triatomines. 2- if postspraying triatomines have a selective advantage, they would have lower FA levels than their prespraying counterparts, whereas if postspraying infestation was positively associated with immigrants not exposed to the insecticide, prespraying and postspraying triatomines would display similar FA levels. For 243 adult T. infestans collected at identified sites before insecticide spraying and 112 collected 4 months postspraying, wing size and wing shape asymmetry was estimated from landmark configurations of left and right sides of each individual. At population level, wing size and shape FA significantly decreased in both females and males after spraying. Males displayed greater wing size and shape FA than females. However, at a single peridomestic site that was persistently infested after spraying, FA declined similarly in females whereas the reverse pattern occurred in males. Our results suggest differential survival of adults with more symmetric wings. This pattern may be related to a selective advantage of survivors to insecticide spraying, which may be mediated or not by their pyrethroid-resistant status or to lower triatomine densities after insecticide spraying and the concomitant increase in feeding success.

Factors associated with the presence of triatomines in rural areas of south Argentine Chaco.

INTRODUCTION: The domestic and peridomestic presence of Triatoma infestans depends on several factors, such as human behavior, vector behavior, ecology, and the environment. METHODS: This work was conducted in 139 domiciliary units, where triatomines were captured and risk factors in domiciles and peridomicilies were recorded. Household dwellers were interviewed to obtain information about practices regarding this disease and entomological indicators were calculated. RESULTS: Infestation indices were 59.7% for house compounds, 4.3% for domestic areas and 58.3% for the peridomestic areas. Intradomicile infestation was significantly associated with housing characteristics. The presence of chicken coops in peridomicilies was associated with an increased risk of infestation. Of the respondents, 80% did not recognize the importance of the peridomiciliary structures for triatomine control and had infested peridomicilies. CONCLUSIONS: The results show the importance of peridomiciles as refuge sites for Triatominae bugs; however, household dwellers do not perceive peridomiciles as areas that favor the presence of vectors. Actions for raising awareness about factors that favor the presence of triatomines are needed to improve the conditions of peridomiciliary environments.

Factors associated with the presence of triatomines in rural areas of south Argentine Chaco

Abstract INTRODUCTION: The domestic and peridomestic presence of Triatoma infestans depends on several factors, such as human behavior, vector behavior, ecology, and the environment. METHODS: This work was conducted in 139 domiciliary units, where triatomines were captured and risk factors in domiciles and peridomicilies were recorded. Household dwellers were interviewed to obtain information about practices regarding this disease and entomological indicators were calculated. RESULTS: Infestation indices were 59.7% for house compounds, 4.3% for domestic areas and 58.3% for the peridomestic areas. Intradomicile infestation was significantly associated with housing characteristics. The presence of chicken coops in peridomicilies was associated with an increased risk of infestation. Of the respondents, 80% did not recognize the importance of the peridomiciliary structures for triatomine control and had infested peridomicilies. CONCLUSIONS: The results show the importance of peridomiciles as refuge sites for Triatominae bugs; however, household dwellers do not perceive peridomiciles as areas that favor the presence of vectors. Actions for raising awareness about factors that favor the presence of triatomines are needed to improve the conditions of peridomiciliary environments.

Temporal variations of fluctuating asymmetry in wing size and shape of Triatoma infestans populations from northwest Argentina.

Environmentally-induced developmental instability has frequently been assessed using fluctuating asymmetry (FA) methods. For Triatoma infestans, the major vector of Chagas disease, the combined effects of host-feeding sources and habitats affected wing developmental instability depending on sex in Figueroa villages, northwest Argentina. Here we investigated whether habitat, sex, season/year and insecticide applications affected wing developmental instability in T. infestans populations from Amamá and other rural villages of northwest Argentina over a four-year period. We measured the occurrence and amount of wing size and shape FA in 423 adult triatomines collected in domiciles, goat corrals, pig corrals, storerooms and wood piles. Significant wing size and wing shape FA occurred in females and males from all habitats as determined by two-way mixed ANOVA and Procrustes ANOVA, respectively. For wing size and shape, the highest corrected indices of FA (FAI) for females occurred in wood piles, goat corrals and domiciles in late summer or early autumn, whereas for males, the largest FAIs consistently appeared in domiciles and storerooms. Wing size FAIs were significantly higher in recently infested goat corrals rather than in persistently infested goat corrals. The follow-up of four infested peridomestic sites showed that FA patterns were not stable over time or sites. Temporal variation of FA among habitats appears to be modified by the history of insecticide spraying, either through direct effects on insect development or through indirect effects related to flight dispersal and house invasion. Whether FA may provide another marker to identify the sources of reinfestant triatomines requires further investigation.

Flower-level developmental plasticity to nutrient availability in Datura stramonium: implications for the mating system.

Background and Aims: Studies of phenotypic plasticity in plants have mainly focused on (1) the effect of environmental variation on whole-plant traits related to the number of modules rather than on (2) the phenotypic consequences of environmental variation in traits of individual modules. Since environmental and developmental factors can produce changes in traits related to the mating system, this study used the second approach to investigate whether within-individual variation in herkogamy-related traits is affected by the environment during plant development in two populations of Datura stramonium , an annual herb with a hypothesized persistent mixed mating system, and to determine which morphological traits may promote self-fertilization. Methods: Full-sib families of two Mexican populations of D. stramonium , with contrasting ecological histories, were grown under low, mid and high nutrient availability to investigate the effects of genetic, environmental and within-plant flower position on flower size, corolla, stamen and pistil lengths, and herkogamy. Key Results: Populations showed differences in familial variation, plasticity and familial differences in plasticity in most floral traits analysed. In one population (Ticumán), the effect of flower position on trait variation varied among families, whereas in the other (Pedregal) the effect of flower position interacted with the nutrient environment. Flower size varied with the position of flowers, but in the opposite direction between populations in low nutrients; a systematic within-plant trend of reduction in flower size, pistil length and herkogamy with flower position increased the probability of self-fertilization in the Pedregal population. Conclusions: Besides genetic variation in floral traits between and within populations, environmental variation affects phenotypic floral trait values at the whole-plant level, as well as among flower positions. The interaction between flower position and nutrient environment can affect the plant's mating system, and this differs between populations. Thus, reductions in herkogamy with flower positions may be expected in environments with either low pollinator abundance or low nutrients.

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

BACKGROUND: The Sordida subcomplex (Triatominae) comprises four species, Triatoma garciabesi, T. guasayana, T. patagonica and T. sordida, which differ in epidemiological importance and adaptations to human environments. Some morphological similarities among species make taxonomic identification, population differentiation and species delimitation controversial. Triatoma garciabesi and T. sordida are the most similar species, having been considered alternatively two and a single species until T. garciabesi was re-validated, mostly based on the morphology of male genitalia. More recently, T. sordida from Argentina has been proposed as a new cryptic species distinguishable from T. sordida from Brazil, Bolivia and Paraguay by cytogenetics. We studied linear and geometric morphometry of the head, wings and pronotum in populations of these species aiming to find phenotypic markers for their discrimination, especially between T. sordida and T. garciabesi, and if any set of variables that validates T. sordida from Argentina as a new species. RESULTS: Head width and pronotum length were the linear variables that best differentiated species. Geometric morphometry revealed significant Mahalanobis distances in wing shape between all pairwise comparisons. Triatoma patagonica exhibited the best discrimination and T. garciabesi overlapped the distribution of the other species in the morphometric space of the first two DFA axes. Head shape showed differentiation between all pairs of species except for T. garciabesi and T. sordida. Pronotum shape did not differentiate T. garciabesi from T. guasayana. The comparison between T. garciabesi and T. sordida from Argentina and T. sordida from Brazil and Bolivia revealed low differentiation based on head and pronotum linear measurements. Pronotum and wing shape were different between T. garciabesi and T. sordida from Brazil and Bolivia and T. sordida from Argentina. Head shape did not differentiate T. garciabesi from T. sordida from Argentina. CONCLUSIONS: Wing shape best delimited the four species phenotypically. The proposed cryptic species, T. sordida from Argentina, differed from T. sordida from Brazil and Bolivia in all measured shape traits, suggesting that the putative new species may not be cryptic. Additional studies integrating cytogenetic, phenotypic and molecular markers, as well as cross-breeding experiments are needed to confirm if these three entities represent true biological species.

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

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