Systematic review on the biology, ecology, genetic diversity and parasite transmission potential of Panstrongylus geniculatus (Latreille 1811) in Latin America.

Panstrongylus geniculatus (Latreille, 1811) is the triatomine with the largest geographic distribution in Latin America. It has been reported in 18 countries from southern Mexico to northern Argentina, including the Caribbean islands. Although most reports indicate that P. geniculatus has wild habitats, this species has intrusive habits regarding human dwellings mainly located in intermediate deforested areas. It is attracted by artificial light from urban and rural buildings, raising the risk of transmission of Trypanosoma cruzi. Despite the wide body of published information on P. geniculatus, many knowledge gaps exist about its biology and epidemiological potential. For this reason, we analysed the literature for P. geniculatus in Scopus, PubMed, Scielo, Google Scholar and the BibTriv3.0 databases to update existing knowledge and provide better information on its geographic distribution, life cycle, genetic diversity, evidence of intrusion and domiciliation, vector-related circulating discrete taxonomic units, possible role in oral T. cruzi transmission, and the effect of climate change on its biology and epidemiology.

Vital Statistics of Triatominae (Hemiptera: Reduviidae) Under Laboratory Conditions: IV. Panstrongylus geniculatus.

A cohort of 100 eggs of Panstrongylus geniculatus (Latreille) was reared in the laboratory under constant conditions (temperature 26 ± 1°C, 60 ± 10% RH), with mortality and fecundity data recorded weekly. We calculated stage-specific development times, age-specific mortality and fecundity (18.4 eggs/♀/wk), and stage-specific and total preadult mortality (31.6%), and the weekly intrinsic rate of natural increase (r(o) = 0.096), the finite population growth rate (λ = 1.109), the net reproductive rate (R(0) = 60.45), and the generation time (T = 46.34 wk). Elasticity analysis showed that the dominant life-history trait determining λ was survival (particularly the adult female's survival). Adult females dominated the stage-specific reproductive value, and the egg stage dominated the stable stage distribution (SSD). The damping ratio (ρ = 1.096) suggests a relatively rapid period of recovery to a disturbed SSD. Results were compared with one previous study and conform relatively well, considering that environmental conditions were not the same. We estimated the colonizing ability of P. geniculatus, using as a criterion the ro/b index, and obtained the value of 0.74, an indicator of a good colonizer, and similar to well-known invasive species such as Rhodnius prolixus and Triatoma infestans. The life history traits and demographic parameters here presented for P. geniculatus are discussed in terms of their usefulness for evolutionary studies and vector control activities.

Genes encoding defensins of important Chagas disease vectors used for phylogenetic studies.

Insects possess both cellular and humoral immune responses. The latter makes them capable to recognize and control invading pathogens after synthesis of a variety of small proteins, also known as antimicrobial peptides. Defensins, cysteine-rich cationic peptides with major activity against Gram-positive bacteria, are one ubiquitous class of antimicrobial peptides, widely distributed in different animal and plant taxa. Regarding triatomines in each of the so far analyzed species, various defensin gene isoforms have been identified. In the present study, these genes were sequenced and used as a molecular marker for phylogenetic analysis. Considering the vectors of Chagas disease the authors are reporting for the first time the presence of these genes in Triatoma sordida (Stål, 1859), Rhodnius nasutus (Stål, 1859), and Panstrongylus megistus (Burmeister, 1835). Members of the Triatoma brasiliensis species complex were included into the study to verify the genetic variability within these taxa. Mainly in their mature peptide, the deduced defensin amino acid sequences were highly conserved. In the dendrogram based on defensin encoding nucleotide, sequences the Triatoma Def3/4 genes were separated from the rest. In the dendrogram based on deduced amino acid sequences the Triatoma Def2/3/4 together with Rhodnius DefA/B pre-propeptides were separated from the rest. In the sub-branches of both the DNA and amino acid dendrograms, the genus Triatoma was separated from the genus Rhodnius as well as from P. megistus.

Machine-learning model led design to experimentally test species thermal limits: The case of kissing bugs (Triatominae).

Species Distribution Modelling (SDM) determines habitat suitability of a species across geographic areas using macro-climatic variables; however, micro-habitats can buffer or exacerbate the influence of macro-climatic variables, requiring links between physiology and species persistence. Experimental approaches linking species physiology to micro-climate are complex, time consuming and expensive. E.g., what combination of exposure time and temperature is important for a species thermal tolerance is difficult to judge a priori. We tackled this problem using an active learning approach that utilized machine learning methods to guide thermal tolerance experimental design for three kissing-bug species: Triatoma infestans, Rhodnius prolixus, and Panstrongylus megistus (Hemiptera: Reduviidae: Triatominae), vectors of the parasite causing Chagas disease. As with other pathogen vectors, triatomines are well known to utilize micro-habitats and the associated shift in microclimate to enhance survival. Using a limited literature-collected dataset, our approach showed that temperature followed by exposure time were the strongest predictors of mortality; species played a minor role, and life stage was the least important. Further, we identified complex but biologically plausible nonlinear interactions between temperature and exposure time in shaping mortality, together setting the potential thermal limits of triatomines. The results from this data led to the design of new experiments with laboratory results that produced novel insights of the effects of temperature and exposure for the triatomines. These results, in turn, can be used to better model micro-climatic envelope for the species. Here we demonstrate the power of an active learning approach to explore experimental space to design laboratory studies testing species thermal limits. Our analytical pipeline can be easily adapted to other systems and we provide code to allow practitioners to perform similar analyses. Not only does our approach have the potential to save time and money: it can also increase our understanding of the links between species physiology and climate, a topic of increasing ecological importance.

Structure and function of the stylets of hematophagous Triatominae (Hemiptera: Reduviidae), with special reference to Dipetalogaster maxima.

Kissing bugs (Hemiptera: Reduviidae: Triatominae) are able to bend their rod-like maxillae while searching for blood vessels in the tissue of their vertebrate hosts. Little is known about the working mechanisms of these bending movements and the distal opening of the food channel. We compared the morphological structure of the stylets (mandibles and maxillae) of four triatomine species and analyzed the feeding process of Dipetalogaster maxima (Uhler, 1894). The maxillae of triatomine bugs are interlocked by a tongue-and-groove system, allowing longitudinal sliding. While penetrating the host tissue, the animals perform rapid alternate back and forth movements of the maxillae. The resistance of the surrounding tissue pushes the asymmetric apex of the maxillae away from its straight path, i.e., if one individual maxilla is protracted alone, its tip curves inwards, and the other maxilla follows. Once a blood vessel is tapped, the spine-like tip of the left maxilla splays outwards. Apically, each of the maxillae features an abutment, the left one exhibiting a notch that presumably facilitates splaying. The mechanical interaction of the two maxillary abutments enables the distal opening of the food channel but might also support the movements of the maxillary bundle attributable to different bending moment distributions.

The development of Panstrongylus herreri under fluctuating environmental conditions.

INTRODUCTION: Panstrongylus herreri is a main Chagas disease vector, and its success as a vector stems from its ability to establish domiciliated colonies; we aimed to explore its biology and reproduction. METHODS: The average amount of blood ingested and the time from the beginning of a blood meal to the production of feces were recorded. RESULTS: Females exhibited a higher blood ingestion rate than males, but similar defecation times and frequencies were observed. CONCLUSIONS: Despite the detected decrease in oviposition rates, P. herreri's potential as a Chagas disease vector in environments other than the Amazon forest cannot be discounted.

Distribution of triatomine species in domestic and peridomestic environments in central coastal Ecuador.

BACKGROUND: Although the central coast of the Ecuador is considered endemic for Chagas disease, few studies have focused on determining the risk of transmission in this region. In this study we describe the triatomine household infestation in Manabí province (Central Coast region), determine the rate of Trypanosoma cruzi infection and study the risk factors associated with infestation by Rhodnius ecuadoriensis. METHODOLOGY/PRINCIPAL FINDINGS: An entomological survey found three triatomine species (Rhodnius ecuadoriensis, Panstrongylus rufotuberculatus and P. howardi) infesting domiciles in 47.4% of the 78 communities visited (total infestation rate of 4.5%). Four percent of domiciles were infested, and nymphs were observed in 77% of those domiciles. The three species were found in altitudes below 500 masl and in all ecological zones except cloud forest. Within the domicile, we found the three species mostly in bedrooms. Rhodnius ecuadoriensis and P. rufotuberculatus were abundant in bird nests, including chicken coops and P. howardi associated with rats in piles of bricks, in the peridomicile. Triatomine infestation was characterized by high rates of colonization, especially in peridomicile. Flagelates infection was detected in only 12% of the samples by microscopy and Trypanosoma cruzi infection in 42% of the examined triatomines by PCR (n = 372). The most important risk factors for house infestation by R. ecuadoriensis were ecological zone (w = 0.99) and presence of chickens (w = 0.96). Determinants of secondary importance were reporting no insecticide applications over the last twelve months (w = 0.86) and dirt floor (w = 0.70). On the other hand, wood as wall material was a protective factor (w = 0.85). CONCLUSION/SIGNIFICANCE: According the results, approximately 571,000 people would be at high risk for T. cruzi infection in Manabí province. A multidisciplinary approximation and the adhesion to a periodic integrated vector management (IVM) program are essential to guarantee sustainable preventive and control strategies for Chagas disease in this region.

Competitive displacement in Triatominae: the Triatoma infestans success.

Brazil has just been certificated by Pan American Health Organization as 'free of Chagas disease transmission due to Triatoma infestans'. During the early 1980s, this species of blood-sucking bug alone was considered responsible for approximately 80% of Chagas disease transmission. But it was not always so. The species originally abundant in houses of central and eastern Brazil was Panstrongylus megistus, which seems to have been progressively displaced from houses by T. infestans during the past century. Indeed, T. infestans seems able to displace other Triatominae in artificial environments. Recent studies suggest that it might simply be because T. infestans feeds more efficiently than its Triatominae competitors.

[Feeding sources evaluation of Panstrongylus lutzi (Neiva & Pinto, 1923) (Hemiptera: Reduviidae: Triatominae) in the State of Ceará]. / Estudo das fontes alimentares de Panstrongylus lutzi (Neiva & Pinto, 1923) (Hemiptera: Reduviidae: Triatominae) no Estado do Ceará.

The authors used precipitin technique to detect the feeding sources of Panstrongylus lutzi (Neiva & Pinto, 1923) in 20 municipalities of Ceará State, Brazil. The results detected the presence of blood from eight different blood sources and mixed feedings, demonstrating that Panstrongylus lutzi is an eclectic species. High infection rates for Trypanosoma like-cruzi were detected.

[Rupestrian triatomines infected by Trypanosomatidae, collected in Quaraí, Rio Grande do Sul, 2003]. / Triatomíneos rupestres infectados por Trypanosomatidae, coletados em Quaraí, Rio Grande do Sul, 2003.

Rupestrian triatomines were captured in six Quaraí city localities, RS, to verify the level of Trypanosomatidae infection, as well as the animal reservoir. The capture occurred in a wild environment and 453 samples were collected, which were identified and separated by nymphal instar. 421 (92.9%) samples of Triatoma rubrovaria, 26 (5.7%) of Triatoma circummaculata and 6 (1.3%) of Panstrongylus tupynambai were collected. Only 13 samples (4.2%) of Triatoma rubrovaria presented Trypanosomatidae infection. After mice and LIT culture inoculation, five strains of Trypanosoma cruzi were isolated. Of these triatomines, 4 (30.8%) displayed no reagent precipitin for the antiserum tested, 4 (30.8%) were positive for rodent antiserum, 4 (30.8%) were positive for goat antiserum and 1 (7.7%) were positive for human and pig antiserum.

Stridulatory sound emission of Panstrongylus rufotuberculatus Champion, 1899, (Hemiptera: Reduviidae: Triatominae).

This study contains the first report of stridulatory sound observed in Panstrongylus rufotuberculatus Champion, 1899, and also a new record of this species in Venezuela. The conditions in which stridulation occurred are described, as well as the general environmental characteristics of the localities where it was found. This triatomine only performs the sound in conditions of extreme provocation.

Life Cycle, Feeding, and Defecation Patterns of Panstrongylus chinai (Hemiptera: Reduviidae: Triatominae) Under Laboratory Conditions.

Chagas disease is caused by the protozoan Trypanosoma cruzi Panstrongylus chinai (Del Ponte) is highly domiciliated in the Peruvian and Ecuadorian Andes and has been found naturally infected with T. cruzi The objective of this study was to describe the life cycle, feeding, and defecation patterns of P. chinai in the Loja province within southern Ecuador. To characterize its life cycle, a cohort of 70 individuals was followed from egg to adult. At each stage of development, prefeeding time, feeding time, weight of ingested meal, proportional weight increase, and the time to the first defecation were recorded. Panstrongylus chinai completed its development in 371.4 ± 22.3 d, (95% CI 355.4-387.4), which means that it is likely a univoltine species. Prefeeding time, feeding time, and weight of ingested meal increased as individuals developed through nymphal stages. Moreover, time to first defecation was shortest in the early nymphal stages, suggesting higher vector potential in the early developmental stages. Data obtained in this study represent an important advance in our knowledge of the biology of P. chinai, which should be considered as a secondary Chagas disease vector species in the Andean valleys of Loja (Ecuador) and in the north of Peru, and included in entomological surveillance programs.

Systematic review on the biology, ecology, genetic diversity and parasite transmission potential of Panstrongylus geniculatus (Latreille 1811) in Latin America

Panstrongylus geniculatus (Latreille, 1811) is the triatomine with the largest geographic distribution in Latin America. It has been reported in 18 countries from southern Mexico to northern Argentina, including the Caribbean islands. Although most reports indicate that P. geniculatus has wild habitats, this species has intrusive habits regarding human dwellings mainly located in intermediate deforested areas. It is attracted by artificial light from urban and rural buildings, raising the risk of transmission of Trypanosoma cruzi. Despite the wide body of published information on P. geniculatus, many knowledge gaps exist about its biology and epidemiological potential. For this reason, we analysed the literature for P. geniculatus in Scopus, PubMed, Scielo, Google Scholar and the BibTriv3.0 databases to update existing knowledge and provide better information on its geographic distribution, life cycle, genetic diversity, evidence of intrusion and domiciliation, vector-related circulating discrete taxonomic units, possible role in oral T. cruzi transmission, and the effect of climate change on its biology and epidemiology.

Abundance, natural infection with trypanosomes, and food source of an endemic species of triatomine, Panstrongylus howardi (Neiva 1911), on the Ecuadorian Central Coast.

The elimination of domestic triatomines is the foundation of Chagas disease control. Regional initiatives are eliminating introduced triatomine species. In this scenario, endemic triatomines can occupy the ecological niches left open and become a threat to long-term Chagas disease control efforts. This study determined the abundance, colonization, and Trypanosoma cruzi infection rate of the endemic Panstrongylus howardi in 10 rural communities located in Ecuador's Manabí Province. In total, 518 individuals of P. howardi were collected. Infestation indices of 1.4% and 6.6% were found in the domestic and peridomestic environments, respectively. We determined a T. cruzi infection rate of 53.2% (N = 47) in this species. P. howardi has a high capacity to adapt to different habitats, especially in the peridomicile. This implies a considerable risk of transmission because of the frequency of intradomicile invasion. Therefore, this species needs to be taken into account in Chagas control and surveillance efforts in the region.

Risks associated with dispersive nocturnal flights of sylvatic Triatominae to artificial lights in a model house in the northeastern plains of Colombia.

BACKGROUND: Control initiatives and continuous surveillance of vector-borne transmission have proved to be effective measures for diminishing the incidence of Chagas disease in endemic countries. However, the active dispersal of infected sylvatic adult triatomines by flight represents one of the main obstacles to eliminating domestic transmission. METHODS: In order to determine the risk that active dispersal of sylvatic adult triatomines represents in Colombian northeastern plains, we quantified the distribution and abundance of triatomines in palm trees (primarily Attalea butyracea) using live bait traps. Directional light traps were used to estimate the frequency of sylvatic triatomine dispersal and their possible origin. Finally, the effect of environmental parameters and artificial light sources on the take-off of sylvatic Rhodnius prolixus was evaluated in field experiments. RESULTS: R. prolixus was found in 90 % of the palm trees that densely aggregated toward the northern portion of the study area. R. prolixus, and three other sylvatic triatomine species were found to actively disperse and were attracted to the directional light traps (Triatoma maculata, Panstrongylus geniculatus and Psammolestes arthuri). Temperature, relative humidity, wind speed and night luminosity did not affect the active dispersal of the triatomines which is higher the first two hours after sunset. Artificial lights from houses at 60 and 110 m played a key role in the directionality of the R. prolixus take-offs. Trypanosoma cruzi was isolated from R. prolixus, T. maculata and P. geniculatus and was genotyped as T. cruzi I, III and IV. CONCLUSIONS: Our results highlight the potential risk in Colombian northeastern plains of actively dispersing sylvatic triatomines and their role in the domestic introduction of Discrete Typing Units of T. cruzi associated to sylvatic foci of Chagas disease transmission.

Host availability limits population density of Panstrongylus megistus.

In order to determine whether host availability limits triatomine population growth, 5th-stage Panstrongylus megistus were maintained in feeding chambers containing 0, 1, 2, or 3 mice. During the 5-day feeding period, triatomines exposed to two or three mice gained significantly more weight than did bugs exposed to one mouse. In addition, half of the bugs exposed to two or three mice molted, as compared to one-fifth of the P. megistus exposed to one mouse. Thus, weight gain and molting were related to host density. In contrast, bug mortality was related to the triatomine-mouse ratio, being greatest among bugs exposed to one mouse. Twenty-nine nonplastered mud-stick houses in a Chagas' disease endemic area were censused and examined for triatomines. About 70% of houses with greater than or equal to 4 persons contained dense bug populations, while only 20% of houses with 1-3 persons were densely infested. Moreover, blood-meal identifications demonstrated that two-thirds of the P. megistus collected from these houses fed on man. The density of triatomines present in infested houses is related to the number of persons available as hosts.

Aggregation behaviour in Panstrongylus megistus and Triatoma infestans: inter and intraspecific responses.

We tested the aggregation response to inter and intraspecific chemical signals in Panstrongylus megistus and Triatoma infestans. As previously described for T. infestans, larvae of P. megistus significantly aggregated on papers impregnated with their own excrement and on papers marked with cuticular substances deposited on surfaces on which these insects had walked. T. infestans bugs also aggregated on papers impregnated by faeces or by cuticular substances of P. megistus, and P. megistus aggregated on papers contaminated by faeces or by cuticular substances of T. infestans. The response of P. megistus to its cuticular substances was significantly stronger than that to its faeces. The non-specificity of the two signals is discussed in the context of the ecological relationship between both species.

Variability of the salivary proteins of 20 Brazilian populations of Panstrongylus megistus (Hemiptera: Reduviidae: Triatominae).

The objective of the present study was to study variability in the salivary proteins of 20 Panstrongylus megistus populations from different ecotopes and verify whether this variability influenced the intensity of the response to specific anti-saliva antibodies. Electrophoretic analysis of P. megistus saliva showed a complex protein composition and great interpopulation variability. A higher concentration of bands was observed in the 17-29 kDa region. The phenogram constructed from the electrophoretic profiles of the P. megistus study populations revealed the existence of two main groups. However, there was no evident relationship between these groups and geographical regions, ecotopes or hosts. Saliva inoculated by P. megistus during feeding elicited production of low level of anti-saliva antibodies in rabbit. The homologous and heterologous salivary proteins were recognised by serum of rabbit sensitised with saliva from only one population. Qualitative and quantitative differences were observed for recognised bands in the saliva of all eight populations studied by Western blot analysis. The most recognised bands were those of greatest molecular weight (68.0-97.4 kDa).

Experimentally induced heat-shock tolerance in Panstrongylus megistus (Hemiptera: Reduviidae).

The survival and molting incidence of fifth-instar nymphs of Panstrongylus megistus (Burmeister, 1835), a vector of Chagas' disease, were investigated following sequential heat shocks in which a mild shock (35 or 40 degrees C, 1 h) preceded a more drastic one (40 degrees C, 12 h). The shocks were separated by 8-, 18-, 24-, or 72-h periods at 28 degrees C. The heat-shock tolerance response was more effective when the first shock was given at 40 degrees C. When the period between shocks was 18 h, the tolerance to sequential shocks (in terms of specimen survival) weakened, which suggested a transient control of the process that enables the organism to circumvent the unfavorable effects of severe shock. In terms of molting incidence, the heat-shock tolerance was only demonstrated when the period between the first shock at 40 degrees C for 1 h and the second shock at 40 degrees C for 12 h was > or = 24 h. These results are the first to demonstrate the induction of heat-shock tolerance in a blood-sucking hemipteran.

Dynamics of thermopreference in the Chagas disease vector Panstrongylus megistus (Hemiptera: Reduviidae).

The thermopreference of resting P. megistus (Burmeister, 1834) adults was studied in a temperature gradient. We also determined the thermopreference for oviposition and ecdysis. Thermopreference of resting individuals depended on the feeding state of the insects. Results demonstrated an initial resting preference of approximately 290 degrees C, which gradually changed to 26-27 degrees C with increasing starvation. A daily variation in thermopreference was also observed with this species. The insects showed a daily maximum preference at the beginning of the dark phase, and a minimum preference during the first half of the light phase. Ecdysis took place all along the gradient, but exhibited a maximum frequency at 30 degrees C. Most eggs were found between 25 and 29 degrees C. Results are discussed in relation to the ecology of P. megistus as compared with other related species, and the existence of mechanisms of behavioral thermoregulation in the group.