Abstract: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.

AbstractIn 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.

AbstractINTRODUCTION: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.

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.