Abstract
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. 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. 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. 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.
Highlights
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
Twenty populations were manually collected in the peridomiciles of eight endemic areas of Triângulo Mineiro (Carneirinho, Frutal, Gurinhatã, Iturama, Limeiro do Oeste, São Francisco de Sales, Tupaciquara, and União de Minas), where the National Program of Chagas Disease Control (NPCDC) was employed for the past 30 years, with continuous and systematic applications of insecticides with residual action (Figure 1)
Deltamethrin and alphacypermethrin, the insecticides used by the Brazilian government for Triatominae control, are pyrethroid insecticides
Summary
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. sordida populations from Triângulo Mineiro area of Minas Gerais. Results: The deltamethrin susceptibility profile of T. sordida populations revealed resistance ratios ranging from 0.84 to 2.8. Triângulo Mineiro, State of Minas Gerais, Brazil, is an old colonization area, cleared by pioneers at the end of the past century during their search for gold and precious stones. By the end of the 1980s, the region was characterized by a small strip of land, with a small population that owned large properties This region is the center for large agroindustrial projects, such as livestock, represented by large cattle-producers, the main economic activity of the region(2). In 1982, the chlorinated insecticide hexachlorobenzene (HCB), used in field control strategies, was replaced with pyrethroids (deltamethrin)(3) By using this insecticide, Triatoma infestans was eradicated from the area. Data for 20102015, from the Health Secretariat of the State of Minas Gerais, revealed that T. sordida was the most captured triatomine (22,337 specimens), representing 92.3% of sampled triatomines, followed by P. megistus (4.5%), R. neglectus (1.2%), and other (2.0%) species (ML Ferraz: Personal Communication, 2015)
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