Feeding behavior of Triatoma vitticeps (Reduviidae: Triatominae) in the state of Minas Gerais, Brazil

The objective of this study was to evaluate the feeding behavior of Triatoma vitticeps through the identification of its food sources and the characterization of the blood ingestion process. In addition, we aimed to verify if the saliva of this vector interferes with the perception of the host during the feedings by creating a nervous impulse. Here, we demonstrated that the T. vitticeps saliva reduces, gradually and irreversibly, the amplitude of the compound action potential of the nervous fibre, which helps decrease the perception of the insect by the host. The precipitin reaction demonstrated the feeding eclecticism of this vector, with the identification of eight food sources - most of them found simultaneously in the same insect. The analysis of the electrical signals produced by the cibarial pump during meals demonstrated that the best feeding performance of T. vitticeps nymphs that fed on pigeons is mainly due to the higher contraction frequency of the pump. The longer contact period with the host to obtain a complete meal compared with other triatominae species of the same instar could favor the occurrence of multiple blood sources in T. vitticeps under natural conditions, as it was evidenced by the precipitin test.

Dispersal of Triatoma infestans and other Triatominae species in the arid Chaco of Argentina: Flying, walking or passive carriage? The importance of walking females

The aim of this paper was to analyse the active dispersal of Triatoma infestans and the role of chickens as passive carriers of this insect in peridomestic areas of La Rioja, Argentina. To measure active dispersal, monthly catches were made on six consecutive nights for five months (in the warm season) using light traps (for flying insects) and sticky dispersal barriers (for walking insects). The nutritional and reproductive states of adults were evaluated. Over the course of the sampling period, a total of eight flying adults, six walking nymphs and 10 walking adults of the species T. infestans were captured, as well as specimens of Triatoma guasayana, Triatoma eratyrusiformis and Triatoma platensis. Our data demonstrate for the first time that females of T. infestans can disperse by walking. This may be an adaptive strategy because it allows them to move with eggs and/or with good blood reserves, which are not possible when flying. All flying and walking individuals of both genders were of an appropriate physiological state that would allow for colonisation of the target habitat. However, manual inspection of 122 chickens suggests that it is unlikely that these animals passively transport T. infestans. Finally, the dispersal activity of T. infestans was compared with other triatomines using a dispersion index.

Evaluation of RbCl and CrCl3 as markers of Triatoma brasiliensis (Hemiptera: Reduviidae) nymphs: persistence and influence of Rb and Cr on triatomine biology

In order to mark Triatoma brasiliensis, the vector of Chagas disease in Brazil, two chemical compounds, rubidium chloride (RbCl) and chromium chloride (CrCl3), were tested. First, 199 N2-N5 nymphs were fed on blood with 0.025M RbCl. Rb marker positivity ranged from 2.5% (N3)-70% (N2), with a maximum persistence of 98 days. Second, 265 N2-N5 nymphs were fed on blood containing 0.0015M CrCl3. Cr marker positivity ranged up to 93% (N5), with a maximum persistence of 119 days. Finally, we blood fed 213 T. brasiliensis to investigate whether CrCl3 altered the biology of this insect. The developmental time of T. brasiliensis was unaltered, but the survival of the Cr-marked group was lower than that of the control group. Differences in the mean fecundity of the control (mean of 156.1) and experimental (mean of 135.6) groups were not statistically significant and 100% of the egg batches of females Cr-marked as nymphs were positive. In conclusion, CrCl3 is a useful tool for marking T. brasiliensis nymphs due to its high positivity and persistence.

The biology of three Mexican-American species of Triatominae (Hemiptera: Reduviidae): Triatoma recurva, Triatoma protracta and Triatoma rubida

The values of biological parameters related to hatching, lifespan, the number of blood meals between moults, mortality, time lapse before the beginning of feeding, feeding time and defecation delay for each instar of three Mexican-American species of Triatominae, Triatoma recurva, Triatoma protracta (former subspecies protracta) and Triatoma rubida (former subspecies uhleri), were evaluated and compared. No significant (p > 0.05) differences were recorded among the three species with respect to the average time required to hatch. This time was approximately 19 days. The average egg-to-adult development time was significantly (p < 0.05) shorter for T. rubida. The number of blood meals at each nymphal instar varied from one-five for each species. The mortality rates were higher for the first-instar nymphs of the three species studied. The mean time lapse before the beginning of feeding was between 0.3-3 min for most nymphs of all instars of each species studied. The mean feeding time was the longest for T. recurva, followed by T. protracta. The defecation delay was less than 10 min for T. recurva and T. rubida. Given these results, only T. rubida should be considered an important potential vector of Trypanosoma cruzi transmission to humans in areas of Mexico where these species exist, whereas T. recurva and T. protracta would be of secondary importance.

Toxicity of non-pyrethroid insecticides against Triatoma infestans (Hemiptera: Reduviidae)

Triatoma infestans (Klug) is the main vector of Chagas disease, which is a public health concern in most Latin American countries. The prevention of Chagas disease is based on the chemical control of the vector using pyrethroid insecticides. In the last decade, different levels of deltamethrin resistance have been detected in certain areas of Argentina and Bolivia. Because of this, alternative non-pyrethroid insecticides from different chemical groups were evaluated against two T. infestans populations, NFS and El Malá, with the objective of finding new insecticides to control resistant insect populations. Toxicity to different insecticides was evaluated in a deltamethrin-susceptible and a deltamethrin-resistant population. Topical application of the insecticides fenitrothion and imidacloprid to first nymphs had lethal effects on both populations, producing 50% lethal dose (LD50) values that ranged from 5.2-28 ng/insect. However, amitraz, flubendiamide, ivermectin, indoxacarb and spinosad showed no insecticidal activity in first instars at the applied doses (LD50 > 200 ng/insect). Fenitrothion and imidacloprid were effective against both deltamethrin-susceptible and deltamethrin-resistant populations of T. infestans. Therefore, they may be considered alternative non-pyrethroid insecticides for the control of Chagas disease.

The residual efficacy of a cypermethrin pour-on formulation applied on goats on the mortality and blood intake of Triatoma infestans

Triatoma infestans is the main vector of Trypanosoma cruzi, the aetiological agent of Chagas disease in the Gran Chaco region of South America. As a frequent blood meal source for triatomine bugs, domestic goats play a key role in the eco-epidemiology of Chagas disease. The aim of this study was to evaluate the mortality and blood intake of T. infestans fed on goats that had been treated with different doses of pour-on insecticide. Third-instar nymphs were fed on goats that had been treated with 0 cc, 5 cc, 10 cc or 15 cc of a pour-on formulation of cypermethrin. The exposure of T. infestans to animals treated at different post-application intervals revealed a residual activity of the insecticide. The mortality rate in the treated groups was higher than in the control groups until 30 days post-insecticide application (p = 0.03), except in the group treated with 5 cc, in which no mortality was detected after seven days of insecticide application. Rainfall affected the triatomicide effect, reducing the time of residual activity. The cypermethrin pour-on treatment decreased the blood intake of T. infestans. Thirty days after the cypermethrin application, nymph mortality was 16% (± 13) with both doses (10 cc and 15 cc). The 15 cc dose did not result in higher insect mortality or increased persistence compared to the 10 cc dose.

Susceptibility and resistance to deltamethrin of wild and domestic populations of Triatoma infestans (Reduviidae: Triatominae) in Bolivia: new discoveries

Bolivia is a high-endemic country for Chagas disease, for which the principal vector is Triatoma infestans (Triatominae). This is a mainly domestic species that is also found in the wild environment. Recently, an increasing number of studies have shown the importance of Triatominae resistance to insecticides, especially in Bolivia. Data regarding the susceptibility/resistance of wild and domestic populations of T. infestans to deltamethrin are presented. For the first time, domestic populations of the department of Santa Cruz were tested, showing low resistance. Although most of the wild populations were found to be susceptible to deltamethrin, three populations from three departments showed a mortality rate of less than 100%. This result is emphasised here.

Potential sources of Triatoma infestans reinfesting peridomiciles identified by morphological characterization in Los Llanos, La Rioja, Argentina

The presence of Triatoma infestans in habitats treated with insecticides constitutes a frequent problem in endemic areas. Basing our study on the hypothesis that descendants of a residual population should be more similar to the pre-treatment population than to any other, we compared the indications of two quantitative morphological approaches. This study seeks to find the origin of 247 T. infestans from three populations found in two chicken coops and a goat corral after treatment with insecticides. The results obtained by quantitative morphology suggest that the T. infestans found between three-34 months after the application of insecticides formed mixed populations with insects derived from residual foci and neighbouring habitats. Our analyses also showed the presence of a phenotype which does not resemble neither the pre-treatment phenotype nor the one from neighbouring populations, suggesting the presence of a particular post-treatment phenotype. The heads size showed some variations in males from different populations and remained unchanged in females, which reinforces the hypothesis of an intraspecific competition for food with priority for females. This article presents, for the first time, the combined analysis of geometric morphometry of heads and antennal phenotypes to identify the composition of reinfesting populations.

New structures for goat corrals to control peridomestic populations of Triatoma infestans (Hemiptera: Reduviidae) in the Gran Chaco of Argentina

Goat production is an important economic activity for rural communities in the Gran Chaco of Argentina. Goat corrals are important for the survival of peridomestic populations of Triatoma infestans. This study evaluated the impact of modifying the traditional structure of goat corrals on T. infestans populations and goat productivity in the region of Los Llanos (La Rioja). Thirty-nine experimental corrals were constructed and 57 traditional corrals were used as controls. We evaluated the infestations of the control and experimental corrals for five years following construction of the structures. The results showed that the new structures did not prevent the colonization, although it enhanced the detection of infestation at low densities of T. infestans. No significant difference was found in T. infestans population abundance between control and experimental corrals, probably because of the different detectability in the two types of structures, especially among the small nymphs. Although goat productivity average was higher in experimental than in control corrals, no significant difference was found because of high variability. The new structures can be used as a complement to promote the development of rural communities. Acceptability and adoption of the new corrals by the owners was high, as the enclosures offered better protection for the goats, increased growth of kids and facilitated herd handling.

Novel polymerase chain reaction-restriction fragment length polymorphism assay to determine internal transcribed spacer-2 group in the Chagas disease vector, Triatoma dimidiata (Latreille, 1811)

Triatoma dimidiata is the most important Chagas disease insect vector in Central America as this species is primarily responsible for Trypanosoma cruzi transmission to humans, the protozoan parasite that causes Chagas disease. T. dimidiata sensu lato is a genetically diverse assemblage of taxa and effective vector control requires a clear understanding of the geographic distribution and epidemiological importance of its taxa. The nuclear ribosomal internal transcribed spacer 2 (ITS-2) is frequently used to infer the systematics of triatomines. However, oftentimes amplification and sequencing of ITS-2 fails, likely due to both the large polymerase chain reaction (PCR) product and polymerase slippage near the 5' end. To overcome these challenges we have designed new primers that amplify only the 3'-most 200 base pairs of ITS-2. This region distinguishes the ITS-2 group for 100% of known T. dimidiata haplotypes. Furthermore, we have developed a PCR-restriction fragment length polymorphism (RFLP) approach to determine the ITS-2 group, greatly reducing, but not eliminating, the number of amplified products that need to be sequenced. Although there are limitations with this new PCR-RFLP approach, its use will help with understanding the geographic distribution of T. dimidiata taxa and can facilitate other studies characterising the taxa, e.g. their ecology, evolution and epidemiological importance, thus improving vector control.

Triatoma jatai sp. nov. in the state of Tocantins, Brazil (Hemiptera: Reduviidae: Triatominae)

Triatoma jatai sp. nov. is the first new species of triatomine to be described in the state of Tocantins, in the northern region of Brazil. It was caught on rock outcrops in the wild environment and, more recently, invading homes. While T. jatai sp. nov. is morphologically similar to Triatoma costalimai, it is distinguished by its general colouring, differences in the blotches on the connexivum, wing size in females and external structures of the male genitalia. The type series has been deposited in the Entomological Collection and Herman Lent Collection, Oswaldo Cruz Institute-Oswaldo Cruz Foundation, Rio de Janeiro, Brazil.

The cuticular hydrocarbons of the Triatoma sordida species subcomplex (Hemiptera: Reduviidae)

The cuticular hydrocarbons of the Triatoma sordida subcomplex (Hemiptera: Reduviidae: Triatominae) were ana-lysed by gas chromatography and their structures identified by mass spectrometry. They comprised mostly n-alkanes and methyl-branched alkanes with one-four methyl substitutions. n-alkanes consisted of a homologous series from C21-C33 and represented 33-45% of the hydrocarbon fraction; n-C29 was the major component. Methyl-branched alkanes showed alkyl chains from C24-C43. High molecular weight dimethyl and trimethylalkanes (from C35-C39) represented most of the methyl-branched fraction. A few tetramethylalkanes were also detected, comprising mostly even-numbered chains. Several components such as odd-numbered 3-methylalkanes, dimethylalkanes and trimethylalkanes of C37 and C39 showed patterns of variation that allowed the differentiation of the species and populations studied. Triatoma guasayana and Triatoma patagonica showed the most distinct hydrocarbon patterns within the subcomplex. The T. sordida populations from Brazil and Argentina showed significantly different hydrocarbon profiles that posed concerns regarding the homogeneity of the species. Triatoma garciabesi had a more complex hydrocarbon pattern, but it shared some similarity with T. sordida. The quantitative and qualitative variations in the cuticular hydrocarbons may help to elucidate the relationships between species and populations of this insect group.

Revalidation and redescription of Triatoma brasiliensis macromelasoma Galvão, 1956 and an identification key for the Triatoma brasiliensis complex (Hemiptera: Reduviidae: Triatominae)

Triatoma brasiliensis macromelasoma is revalidated based on the results of previous multidisciplinary studies on the Triatoma brasiliensis complex, consisting of crossing experiments and morphological, biological, ecological and molecular analyses. These taxonomic tools showed the closest relationship between T. b. macromelasoma and Triatoma brasiliensis brasiliensis. T. b. macromelasoma is redescribed based on specimens collected in the type locality and specimens from a F1 colony. The complex now comprises T. b. brasiliensis, T. b. macromelasoma, Triatoma melanica, Triatoma juazeirensis and Triatoma sherlocki. An identification key for all members of the complex is presented. This detailed comparative study of the morphological features of T. b. macromelasoma and the remaining members of the complex corroborates results from multidisciplinary analyses, suggesting that the subspecific status is applicable. This subspecies can be distinguished by the following combination of features: a pronotum with 1+1 narrow brownish-yellow stripes on the submedian carinae, not attaining its apex, hemelytra with membrane cells darkened on the central portion and legs with an incomplete brownish-yellow ring on the apical half of the femora. Because the T. brasiliensis complex is of distinct epidemiological importance throughout its geographic distribution, a precise identification of its five members is important for monitoring and controlling actions against Chagas disease transmission.

Toxicological and biochemical analysis of the susceptibility of sylvatic Triatoma infestans from the Andean Valley of Bolivia to organophosphate insecticide

To increase our knowledge of the natural susceptibility of Triatoma infestans to an organophosphate insecticide, we performed toxicological and biochemical studies on three sylvatic populations from Bolivia and two populations from domestic dwellings from Bolivia and Argentina. Fifty-per-cent lethal doses (LD50) were determined based on the topical application of fenitrothion on first instar nymphs and mortality was assessed at 24 h. Both type of populations exhibited LD50ratios significantly higher than 1 with a range of the values (1.42-2.47); the maximum value were found in a sylvatic (-S) population, Veinte de Octubre-S. Samples were biochemically analysed using a glutathione S-transferase activity assay. The highest significant activity was obtained for Veinte de Octubre-S and the lowest activity was obtained for the reference population (102.69 and 54.23 pmol per minute per mg of protein respectively). Two out of the three sylvatic populations (Veinte de Octubre-S and Kirus Mayu-S) exhibited significantly higher glutathione S-transferase activity than that of the reference population. Based on this analysis of the natural susceptibility of this organism to organophosphate insecticides, continental and focal surveys of organophosphate susceptibility should be conducted to evaluate the evolution and distribution of this phenomenon.

Analysing deltamethrin susceptibility and pyrethroid esterase activity variations in sylvatic and domestic Triatoma infestans at the embryonic stage

The aim of the present work was to study the deltamethrin susceptibility of eggs from Triatoma infestans populations and the contribution of pyrethroid esterases to deltamethrin degradation. Insects were collected from sylvatic areas, including Veinte de Octubre and Kirus-Mayu (Bolivia) and from domiciliary areas, including El Palmar (Bolivia) and La Pista (Argentina). Deltamethrin susceptibility was determined by dose-response bioassays. Serial dilutions of deltamethrin (0.0005-1 mg/mL) were topically applied to 12-day-old eggs. Samples from El Palmar had the highest lethal dose ratio (LDR) value (44.90) compared to the susceptible reference strain (NFS), whereas the Veinte de Octubre samples had the lowest value (0.50). Pyrethroid esterases were evaluated using 7-coumaryl permethrate (7-CP) on individually homogenised eggs from each population and from NFS. The El Palmar and La Pista samples contained 40.11 and 36.64 pmol/min/mg protein, respectively, and these values were statistically similar to NFS (34.92 pmol/min/mg protein) and different from Kirus-Mayu and Veinte de Octubre (27.49 and 22.69 pmol/min/mg protein, respectively). The toxicological data indicate that the domestic populations were resistant to deltamethrin, but no statistical contribution of 7-CP esterases was observed. The sylvatic populations had similar LDR values to NFS, but lower 7-CP esterase activities. Moreover, this is the first study of the pyrethroid esterases on T. infestans eggs employing a specific substrate (7-CP).