Genetic characterization of residual Triatoma infestans populations from Brazil by microsatellite.

In spite of long-term efforts to eliminate Triatoma infestans (Klug 1834) from Brazil, residual foci still persist in the states of Bahia and Rio Grande do Sul. Data on the genetic variability and structuring of these populations are however lacking. Using nine microsatellite loci, we characterized one residual T. infestans population from Bahia and four from Rio Grande do Sul, and compared them with bugs originally from an older focus in São Paulo; 224 bugs were genotyped. The number of alleles per locus ranged from 5 to 11. Observed and expected heterozygosities per locus ranged, respectively, from 0 to 0.786 and from 0 to 0.764. Significant departures from Hardy-Weinberg equilibrium, mainly due to heterozygote deficits, were detected in all loci and in most populations. Global indices estimated by AMOVA were: Fis was 0.37; Fst was 0.28; and Fit was 0.55; overall indices with p = 0.00 indicated substantial differentiation. Inter-population Fst ranged from 0.118 to 0.562, suggesting strong genetic structuring and little to no gene flow among populations. Intra-population Fis ranged from 0.301 to 0.307. Inbreeding was apparent in all populations except that from Bahia-which might be either linked by gene flow to nearby unsampled populations or part of a relatively large local population. The overall pattern of strong genetic structuring among pyrethroid-susceptible residual T. infestans populations suggests that their persistence is probably due to operational control failures. Detection and elimination of such residual foci is technically feasible and must become a public health priority in Brazil.

Assessing the mitochondrial DNA diversity of the Chagas disease vector Triatoma sordida (Hemiptera: Reduviidae).

Triatoma sordida is a species that transmits Trypanosoma cruzi to humans. In Brazil, T. sordida currently deserves special attention because of its wide distribution, tendency to invade domestic environments and vectorial competence. For the planning and execution of control protocols to be effective against Triatominae, they must consider its population structure. In this context, this study aimed to characterise the genetic variability of T. sordida populations collected in areas with persistent infestations from Minas Gerais, Brazil. Levels of genetic variation and population structure were determined in peridomestic T. sordida by sequencing a polymorphic region of the mitochondrial cytochrome b gene. Low nucleotide and haplotype diversity were observed for all 14 sampled areas; π values ranged from 0.002-0.006. Most obtained haplotypes occurred at low frequencies, and some were exclusive to only one of the studied populations. Interpopulation genetic diversity analysis revealed strong genetic structuring. Furthermore, the genetic variability of Brazilian populations is small compared to that of Argentinean and Bolivian specimens. The possible factors related to the reduced genetic variability and strong genetic structuring obtained for studied populations are discussed in this paper.

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

BACKGROUND: Chagas disease (CD) is caused by the flagellate protozoan Trypanosoma cruzi and can be carried by different species of triatomines, including Rhodnius neglectus, which is wild, well distributed in Brazil, and has formed colonies in palm trees located in urban areas of municipalities in the state of São Paulo. Chemical control has been routinely used to reduce population density, but each year, there has been an increase in species dispersion and density. This study aimed to evaluate the susceptibility of insects to insecticides used in control. METHODS: The reference population was collected from Araçatuba municipality, Nilce Maia. Dilutions of deltamethrin were prepared and applied to the back of the first-stage nymphs, which were biologically synchronized. The control group received pure acetone only. Mortality was assessed after 72 h. RESULTS: The mortality rate with respect to diagnostic dose was 100%. The susceptibility profile observed for this population showed RR50 ranging from 1.76 to 3.632. CONCLUSIONS: The populations were susceptible to the insecticides tested. It is possible that the insecticide residual effect on this ecotope has decreased the lifespan, and controlling failures may be the cause of recolonization in this environment.

Evaluation of the insecticide susceptibility profile in Cimex lectularius (Hemiptera: Cimicidae) in Belo Horizonte (Brazil).

INTRODUCTION: Since 2013, major Cimex lectularius infestations have been detected in public shelters in Belo Horizonte (Brazil). Due to this, insecticide resistance has been investigated as one of the possible causes for the failure to control bedbugs. METHODS: Cimicids were subjected to bioassays according to the World Health Organization recommendations using deltamethrin and all commercial insecticides available for control of Cimex in Brazil. RESULTS: Cimicids were deltamethrin resistant and presented indicative of resistance to other insecticides, except for propoxur 1%. CONCLUSIONS: The commercial insecticides have a limited effect on bedbug populations, which may justify the unsatisfactory control observed in the shelters studied.

Susceptibility of phlebotomine sandflies (Diptera: Psychodidae) collected in the field, to alpha-cypermethrin in four municipalities endemic to leishmaniasis.

Although the chemical control against leishmaniasis began in 1953 in Brazil, little information is available on how this strategy has affected populations of phlebotomine sandflies in the field. The objective of this study was to analyze the susceptibility profile of four populations of phlebotomine sandflies to the insecticide alpha-cypermethrin. Sandflies collected in field in four Brazilian municipalities were evaluated using CDC bottles in different concentrations of alpha-cypermethrin. A total of 1,186 phlebotomine sandflies were used in the bioassays. The LD50 ranged from 1.48 to 2.57 ug/mL in the field populations. For a dose of 5 ug/mL of alpha-cypermethrin, the LT50 and LT95 ranged from 17.9 to 27.5 minutes, and LT95 from 39.7 to 61.5 minutes, respectively. All the populations studied were highly susceptible to the insecticide alpha-cypermethrin. Routine studies are needed to detect changes in sandflies susceptibility to insecticides.

The role of LuloPAT amino acid/proton symporters in midgut alkalinization in the sandfly Lutzomyia longipalpis (Diptera - Psychodidae).

In Lutzomyia longipalpis females, which are the main vectors of Leishmania infantum in the Americas, hematophagy is crucial for ovary development. The control of pH in the midgut during blood digestion is important to the functioning of the digestive enzymes, which release amino acids in the luminal compartment that are then transported through the enterocytes to the hemolymph for delivery to the ovary and other organs. In the present work, we investigated transport systems known as LuloPATs that are present in the midgut of L. longipalpis but not in other organs. These transporters achieve symport of amino acids with H+ ions, and one of them (LuloPAT1) is orthologous to a transporter described in Aedes aegypti. According to our results, the transcription levels of LuloPAT1 increased significantly immediately after a blood meal. Based on the variation of the fluorescence of fluorescein with the pH of the medium, we developed a technique that shows the acidification of the cytoplasm of gut cells when amino acids are cotransported with H+ from the lumen into the enterocytes. In our experiments, the midguts of the sandflies were dissected and opened longitudinally so that added amino acids could enter the enterocytes via the lumen (PAT carriers are apical). LuloPAT1 transporters are part of a complex of mechanisms that act synergistically to promote gut alkalinization as soon as blood intake by the vector occurs. In dissected but not longitudinally opened midguts, added amino acids could only enter through the basolateral region of enterocytes. However, alkalinization of the lumen was observed because the entry of some amino acids into the cytoplasm of enterocytes triggers a luminal alkalinization mechanism independent of LuloPATs. These findings provide new perspectives that will enable the characterization of the set of signaling pathways involved in pH regulation within the L. longipalpis midgut.

Epidemiological aspects of pediculosis by Pediculus humanus capitis (Phthiraptera: Pediculidae) in Minas Gerais: a systematic review / Aspectos epidemiológicos da pediculose por Pediculus humanus capitis (Phthiraptera: Pediculidae) em Minas Gerais: uma revisão sistemática

Abstract Background Head lice, or head pediculosis, is a parasitosis considered a serious public health problem that affects mainly resource-limited countries. Objective To describe epidemiological aspects of the pediculosis capitis in Minas Gerais, in Brazil. Method This systematic review was conducted through the standards established by the Preferred Reporting Items in Systematic Reviews and Metanalyses (PRISMA). PubMed, LILACS, and SciELO databases, as well as the gray literature, were searched. Results Nine of 1,167 studies were included, published between 1988 and 2019. These studies reported a total prevalence of parasitosis that ranged from 1.4% to 57.4%. The prevalence of head lice ranged from 0.0% to 66.7% for males and 2.3% to 57.4% for females, thus being higher in black-skinned people (1.4% to 40.3%). Regarding age, the highest prevalence was 10-12 years old (45.3%). As for the characteristics of the hair, there was a greater infestation in people with long (16.0% to 79.5%), wavy (0.0% to 44.7%), dark (0.0% to 36.6%), with low capillary density (35.4%), and thick hair (39.2%). Conclusion Head pediculosis affects both sexes, different ages, and races, representing an important health problem in Minas Gerais, not only due to the presence of ectoparasite but also to the secondary complications that can be generated from this parasitism.

Resumo Introdução A pediculose de cabeça é uma parasitose considerada um sério problema de saúde pública, afetando principalmente países com recursos limitados. Objetivo Descrever os aspectos epidemiológicos da pediculose de cabeça em Minas Gerais, Brasil. Método Revisão sistemática conduzida por meio dos padrões estabelecidos pelo Preferred Reporting Items in Systematic Reviews and Metanalyses (PRISMA). Foram pesquisadas as bases de dados PubMed, LILACS e SciELO, bem como a literatura cinza. Resultados Nove de 1.167 estudos foram incluídos, publicados entre 1988 e 2019. Relatou-se uma prevalência total da parasitose que variou de 1,4% a 57,4%. Ela variou de 0,0% a 66,7% para homens e 2,3% a 57,4% para mulheres, sendo maior em pessoas de cor negra (1,4% a 40,3%). Em relação à idade, a maior prevalência foi de 10 a 12 anos (45,3%). Quanto às características dos cabelos, houve maior infestação em pessoas com cabelos longos (16,0% a 79,5%), ondulados (0,0% a 44,7%), escuros (0,0% a 36,6%), com baixa densidade capilar (35,4%) e fios grossos (39,2%). Conclusão A pediculose atinge ambos os sexos, diferentes idades e raças, representando um importante problema de saúde em Minas Gerais, não só pela presença do ectoparasita, mas também pelas complicações secundárias que podem ser geradas desse parasitismo.

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

ABSTRACT Background: Chagas disease (CD) is caused by the flagellate protozoan Trypanosoma cruzi and can be carried by different species of triatomines, including Rhodnius neglectus, which is wild, well distributed in Brazil, and has formed colonies in palm trees located in urban areas of municipalities in the state of São Paulo. Chemical control has been routinely used to reduce population density, but each year, there has been an increase in species dispersion and density. This study aimed to evaluate the susceptibility of insects to insecticides used in control. Methods: The reference population was collected from Araçatuba municipality, Nilce Maia. Dilutions of deltamethrin were prepared and applied to the back of the first-stage nymphs, which were biologically synchronized. The control group received pure acetone only. Mortality was assessed after 72 h. Results: The mortality rate with respect to diagnostic dose was 100%. The susceptibility profile observed for this population showed RR50 ranging from 1.76 to 3.632. Conclusions: The populations were susceptible to the insecticides tested. It is possible that the insecticide residual effect on this ecotope has decreased the lifespan, and controlling failures may be the cause of recolonization in this environment.

Monitoring Rhodnius neglectus (Lent, 1954) populationssusceptibility to insecticide used in controlling actions inurban areas northwest of São Paulo state

Background: Chagas disease (CD) is caused by the flagellate protozoan Trypanosoma cruzi and can be carried by different species oftriatomines, including Rhodnius neglectus, which is wild, well distributed in Brazil, and has formed colonies in palm trees located in urban areasof municipalities in the state of São Paulo. Chemical control has been routinely used to reduce population density, but each year, there has beenan increase in species dispersion and density. This study aimed to evaluate the susceptibility of insects to insecticides used in control.Methods: The reference population was collected from Araçatuba municipality, Nilce Maia. Dilutions of deltamethrin were preparedand applied to the back of the first-stage nymphs, which were biologically synchronized. The control group received pure acetone only.Mortality was assessed after 72 h.Results: The mortality rate with respect to diagnostic dose was 100 per cent. The susceptibility profile observed for this population showed RR50ranging from 1.76 to 3.632.Conclusions: The populations were susceptible to the insecticides tested. It is possible that the insecticide residual effect on this ecotopehas decreased the lifespan, and controlling failures may be the cause of recolonization in this environment.

Evaluation of the insecticide susceptibility profile in Cimex lectularius (Hemiptera: Cimicidae) in Belo Horizonte (Brazil)

Abstract INTRODUCTION: Since 2013, major Cimex lectularius infestations have been detected in public shelters in Belo Horizonte (Brazil). Due to this, insecticide resistance has been investigated as one of the possible causes for the failure to control bedbugs. METHODS: Cimicids were subjected to bioassays according to the World Health Organization recommendations using deltamethrin and all commercial insecticides available for control of Cimex in Brazil. RESULTS: Cimicids were deltamethrin resistant and presented indicative of resistance to other insecticides, except for propoxur 1%. CONCLUSIONS: The commercial insecticides have a limited effect on bedbug populations, which may justify the unsatisfactory control observed in the shelters studied.

History of insecticide resistance of Triatominae vectors.

In the last 15 years, different types of Triatominae resistance to different insecticides have been reported; thus, resistance may be more widespread than known, requiring better characterization and delimitation, which was the aim of this review. This review was structured on a literature search of all articles from 1970 to 2015 in the PubMed database that contained the keywords Insecticide resistance and Triatominae . Out of 295 articles screened by title, 33 texts were selected for detailed analysis. Insecticide resistance of Triatomines is a complex phenomenon that has been primarily reported in Argentina and Bolivia, and is caused by different factors (associated or isolated). Insecticide resistance of Triatominae is a characteristic inherited in an autosomal and semi-dominant manner, and is polygenic, being present in both domestic and sylvatic populations. The toxicological profile observed in eggs cannot be transposed to different stages of evolution. Different toxicological profiles exist at macro- and microgeographical levels. The insecticide phenotype has both reproductive and developmental costs. Different physiological mechanisms are involved in resistance. Studies of Triatomine resistance to insecticides highlight three deficiencies in interpreting the obtained results: I) the vast diversity of methodologies, despite the existence of a single guiding protocol; II) the lack of information on the actual impact of resistance ratios in the field; and III) the concept of the susceptibility reference lineage. Research on the biological and behavioral characteristics of each Triatominae species that has evolved resistance is required in relation to the environmental conditions of each region.

Baseline susceptibility to alpha-cypermethrin in Lutzomyia longipalpis (Lutz & Neiva, 1912) from Lapinha Cave (Brazil).

BACKGROUND: Given the increase in cases of visceral leishmaniasis in recent years, associated with the socio-economic impact of this disease, as well as the wide distribution of Lutzomyia longipalpis in Brazil and the likelihood that this vector may develop resistance to insecticides used for control, the Ministry of Health considers as crucial the creation of a network in order to study and monitor the resistance of this vector to insecticides used for control. In this sense, this study aimed: 1) to characterize the susceptibility of L. longipalpis from Lapinha Cave (Lagoa Santa, MG - Brazil) to Alfateck SC200 in field bioassays, and 2) to define the susceptibility baseline to alpha-cypermethrin in laboratory bioassays, checking the possibility of using it as susceptibility reference lineage (SRL). FINDINGS: The field bioassays revealed that the tested population was highly susceptible to alpha-cypermethrin in all time periods with high mortality (~100 %) in all treated surfaces before six months after spraying. In the laboratory bioassays, the studied population presented LD50, LD95 and LD99 to 0.78013, 10.5580 and 31.067 mg/m(2), respectively. The slope was 1.454121. CONCLUSIONS: The studied population of L. longipalpis was considered as adequate for SRL according criterion recommended by Pan-American Health Organization and has proven susceptibility to tested insecticide in the field. One cannot rule out the possibility of finding populations of L. longipalpis more susceptible to alpha-cypermethrin; therefore, further research is necessary on other populations with potential use as a SRL.

Variability of susceptibility to deltamethrin in peridomestic Triatoma sordida from Triângulo Mineiro, State of Minas Gerais, Brazil.

INTRODUCTION: Despite chemical and physical vector control strategies, persistent infestations of Triatoma sordida have been reported in a large part of Minas Gerais, Brazil, and the cause for this is little investigated. We aimed to characterize the deltamethrin toxicological profile in peridomestic T. sordidapopulations from Triângulo Mineiro area of Minas Gerais. METHODS: Susceptibility to deltamethrin was assessed in seventeen peridomestic T. sordida populations. Serial dilutions of deltamethrin in acetone (0.2µL) were topically applied on the first instar nymphs (F1; five days old; fasting weight, 1.2 ± 0.2mg). Dose response results were analyzed using Probit software, and the lethal doses, slope and resistance ratios were determined. Qualitative tests were also performed. RESULTS: The deltamethrin susceptibility profile of T. sordida populations revealed resistance ratios ranging from 0.84 to 2.8. The percentage mortality in response to a diagnostic dose was 100.0% in all populations. CONCLUSIONS: From our results, the lack of resistance to insecticides but persistent T. sordida infestations in the Triângulo Mineiro area may be because of: 1) environmental degradation facilitating dispersion of T. sordida, allowing colonization in artificial ecotopes; 2) operational failures; and 3) complexity of the peridomicile in the study area.These variables are being investigated.

Susceptibility of Triatoma sordida Stal, 1859 (Hemiptera: Reduviidae) to alpha-cypermethrin under natural climatic conditions.

INTRODUCTION: Despite the recommendations by interpretation of resistance ratios obtained in laboratory bioassays, little is known about the actual impact of these results in the effectiveness of vector control activities in the field. In this context, our objective was to determine the mean value of different resistance ratios obtained by laboratory bioassays performed as part of the chemical control strategies of Triatoma sordida in the field. METHODS: Field bioassays were developed in Monte Azul and Coração de Jesus (Southeast, Brazil). In each location, samples were formed with three domestic units treated with alpha-cypermethrin 20.0% (Alfatek (r) 200 SC). One day after spraying, 10 fifth-instar nymphs remained in contact with the surfaces treated (adobe with plaster, adobe without plaster, or wood) with insecticide in plastic cones for 72h. Three cones were exposed inside the intradomicile and the peridomicile. The insects in the control group were exposed to an insecticide-free piece of cardboard. Mortality was measured 72h after removal of the insects from the treated surfaces. The tests were realized in triplicate. RESULTS: Mortality was 100.0% in all locations, except for Monte Azul; Landinho (96.6%) and Coração de Jesus; Barriguda (96.6%). CONCLUSIONS: Although the resistant populations in laboratory tests proved to be susceptible in the field, this observation is not sufficient to suggest that the cut-off points used to justify the resistance ratio should be changed. In this sense, we recommend that laboratory and field bioassays are carried out with a greater number of Triatominae populations to allow more in-depth consideration of the subject.

Toxicological profile of deltamethrin in Triatoma brasiliensis (Hemiptera: Reduviidae) in State of Ceará, Northeastern Brazil.

INTRODUCTION: Triatoma brasiliensis is the species of greatest epidemiological relevance in the semi-arid region of Brazil. This species is predominantly found in domestic environments, and it has the ability to build large colonies with high levels of natural infection via Trypanosoma cruzi. Thus, T. brasiliensis is one of the most efficient transmitters of Chagas disease (CD) to humans. Despite household spraying with residual insecticides, many areas report persistent reinfestations for reasons that remain poorly understood. Therefore, this study sought to characterize the toxicological profile of deltamethrin in T. brasiliensis from areas with persistent reinfestation in State of Ceará, Brazil. METHODS: The susceptibility reference lineage (SRL) was derived from Umari. Serial dilutions of deltamethrin were prepared and applied to the dorsal abdomen of first instar nymphs. The control group received only pure acetone. Mortality was evaluated after 72h. Qualitative tests assessed mortality in response to a diagnostic dose of 1xLD99 (0.851 nanograms of active ingredient per treated nymph) of the SRL. RESULTS: The susceptibility profile characterization of the T. brasiliensis populations revealed 50% resistance ratios (RR50) that ranged from 0.32 to 1.21. The percentage of mortality in response to the diagnostic dose was 100%. CONCLUSIONS: We demonstrated that T. brasiliensis was highly susceptible to deltamethrin. The control difficulties found might be related to the recolonization of the triatomines originating from neighboring environments and the possible operational failures related to the process of spraying that enabled specimens less susceptible to deltamethrin to survive.

Markers for the population genetics studies of Triatoma sordida (Hemiptera: Reduviidae).

BACKGROUND: Triatoma sordida, a vector of Trypanosoma cruzi, is native of Brazil, Bolivia, Paraguay, Argentina, and Uruguay, and occurs primarily in peridomiciles. Currently, it is the species most frequently captured by the Chagas Disease Control Program in Brazil. For this reason, population genetic studies attract great interest, as they can provide further information about the dispersal and household invasion processes of this species. In the absence of suitable markers, the objective of this study was to test the cross amplification of microsatellite primers. FINDINGS: 23 primers were tested for microsatellite loci already described for other species of the genus Triatoma sp. Forty four specimens of T. sordida captured in the north of Minas Gerais were used to validate the use of standardized loci for population genetic analyses. It was possible to amplify 10 of the 23 loci tested for T. sordida. CONCLUSIONS: This is the first study that provides 10 microsatellite markers for population analysis of this triatomine species. Cross-amplification of primers can be used among other phylogenetically related species whose loci are already available for study.

Deltamethrin toxicological profile of peridomestic Triatoma sordida in the North of Minas Gerais, Brazil.

BACKGROUND: In general, there was a large reduction in the occurrence of cases of Chagas disease in the last decades in Brazil. However, despite all of these efforts, there have been various reports of persistent reinfestations of T. sordida in a large part of the state of Minas Gerais, for reasons still little investigated. Thus, this purpose of this study was to characterize the deltamethrin susceptibility profile of peridomestic T. sordida populations from North of Minas Gerais-Brazil. METHODS: Susceptibility to deltamethrin was assessed in seventeen peridomestic populations of T. sordida from North region of Minas Gerais, Brazil. Serial dilutions of deltamethrin in acetone (0.2 µL) were topically applied in first instar nymphs (F1, five days old, fasting, weight 1.2 ± 0.2 mg). Dose response results were analyzed with POLO program, determining the lethal doses, slope and resistance ratios (RR). RESULTS: Susceptibility profile characterization of T. sordida populations revealed resistance ratios (RR50) ranging from 2.50 to 7.08. CONCLUSIONS: In fact, we know very little about the real impact of the resistance ratios obtained in the laboratory bioassays on the effectiveness of the vector control activities in the field. Thus, we prefer to refer to the populations with RR > 5 as populations with altered susceptibility. For these populations, the realization of laboratory and field trials, simultaneous and complementary, permitting the evaluation of both, is recommended.

Standardization of laboratory bioassays for the study of Triatoma sordida susceptibility to pyrethroid insecticides.

BACKGROUND: Increasing reports of high-resistant Triatominae populations concerns scientists and sanitarians as little is known about the factors behind the occurrence of such phenotype and its real impact on vector control strategies. Moreover, the utilization of a large variety of methodologies hinder the comparison of the reported studies. METHODS: This work aims to review laboratory bioassays, redefining the assessed biological features (age, generation and insecticide application area) and technical procedures (mortality recording time and the ideal diagnostic dose). RESULTS: Results were not influenced by the insecticide application area in nymphs or by their generation. Three days-old specimen's revealed lower susceptibility to the tested insecticide. We determined that it is more appropriate to record mortality 72 h after treatment with insecticide, as well as using a diagnostic dose of 1xDL99. CONCLUSION: This work suggests more adequate methodological parameters for assessing insecticide resistance in triatomines, which also allows the comparison of results obtained by different research groups. For laboratory bioassays, we recommend: 1) the use of first instar nymphs from first or second generation; 2) 3 day-old specimens; 2) application of insecticide in the dorsal or ventral abdomen area; 3) mortality recording 72 h after treatment with pyrethroids and 4) a diagnostic dose of 1x LD99.

Susceptibility characterization of residual Brazilian populations of Triatoma infestans Klug, 1834 (Hemiptera: Reduviidae) to deltamethrin pyrethroid.

INTRODUCTION: Despite years of efforts towards the elimination of Triatoma infestans in Brazil, residual foci still persist in some areas of the States of Bahia and Rio Grande do Sul. The persistence of these T. infestans populations in the country has two different origins of equal concern: operational failures or insecticide resistance. Thus, the objective of this study was to characterize the susceptibility profile of the residual Brazilian populations of T. infestans to deltamethrin. METHODS: The susceptibility reference lineage was derived from Cipein/Argentina. The populations studied were manually collected using a dislodging agent in peridomiciles in the States of Bahia (Novo Horizonte) and of Rio Grande do Sul (Santa Rosa and Doutor Maurício Cardoso). Serial dilutions of deltamethrin were prepared and applied at the dorsal abdomen of first instar nymphs. The control group received only pure acetone. Mortality was evaluated after 72h. Qualitative tests assessed the mortality of a diagnostic dose of 1xLD99 (2.76ng a.i./nymph) determined for the susceptibility reference lineage. RESULTS: The susceptibility profile characterization of the T. infestans populations revealed an RR50 ranging from 1.73 to 3.26. The mortality percentage in response to a diagnostic dose was 100%. The results obtained in the quantitative and qualitative assays corresponded for all populations. CONCLUSIONS: The results of this study indicate that the persistence of residual foci of T. infestans in Bahia and Rio Grande do Sul is not related to insecticide resistance but may be associated with operational failures. In Rio Grande do Sul, we must consider the possibility of continuous reinfestation by Argentinian individuals, which justifies active and efficient epidemiological surveillance.

Deltamethrin pyrethroid susceptibility characterization of Triatoma sordida Stål, 1859 (Hemiptera: Reduviidae) populations in the Northern Region of Minas Gerais, Brazil.

INTRODUCTION: Triatoma sordida is the most captured Triatomine species in the Brazilian artificial environment. In 2008, the discovery of three Triatomine populations with altered susceptibilities to deltamethrin highlighted the importance of investigating the genetic potential for resistance in triatomines. The purpose of this study was to characterize the susceptibility to deltamethrin of peridomestic T. sordida populations in Minas Gerais, Brazil. METHODS: A susceptibility reference lineage derived from Uberaba, Minas Gerais, Brazil was used. Serial dilutions of deltamethrin were prepared and applied to the dorsal abdomen of first instar nymphs. The control group received only pure acetone. Mortality was evaluated after 72h. Qualitative tests assessed mortality in response to a diagnostic dose of 1xLD99 of the susceptibility reference lineage. RESULTS: Susceptibility profile characterization of T. sordida populations revealed resistance ratios (RR50s) ranging from 0.42 to 3.94. The percentage mortality in response to the diagnostic dose varied from 70% to 100%. A comparison of the results obtained in the quantitative and qualitative assays demonstrated a lack of correspondence for some populations. CONCLUSIONS: We demonstrated that only T. sordida populations that present a RR50>1.0 have altered susceptibility, and the execution of simultaneous field and laboratory tests is required to understand the actual effect of vector control. A possible cause of the observed resistance ratios might be the continuous use of pyrethroids in Brazil since the 1980s.