Perfil da suscetibilidade a deltametrina em populações de Triatoma sordida (Hemiptera: Reduviidae) do estado de Minas Gerais procedentes de áreas com infestação persistente

Abstract

High insecticide resistance ratios on triatominic populations have been frequently reported, causing impact on vector control strategies and challenging scientists and sanitarists on the quest for novel alternatives concerning vector control. Considering the already reported cases of triatomine resistance, it is possible that the intensive use of insecticides in Brazil for over 30 years caused the emergence of new foci in wider geographic areas. Thus, the investigation of the related phenomenon is justified by its importance. Moreover it is necessary to consider the environmental conditions on which the resistance is inserted, the insects genetic variability and the resistance timeline evolution after exposure to chemical assets. The aim of the present study was to characterize the pyrethroid deltamethrin susceptibility/resistance profile of Triatoma sordida (Stål, 1859) populations from areas with persistent infestation on the Triangulo Mineiro and on northern Minas Gerais. The qualitative and quantitative bioassays were conducted according to PESSOA (2008) and biochemical assays according to VALLE et al., 2006) with modifications. The genetic characterization of triatomine populations was developed through microsatellites transposition technique. The operational and environmental characteristics were assessed through questionnaires. The climatic variables (relative humidity, pluviosity, temperature and solar radiation) were obtained from BDMEP. The quantitative bioassay analyzes showed RR50 ranging from 0.44 to 6.5. According to the criterion of categorization status of susceptibility / resistance proposed by PAHO (2005), only 1% of the population was classified as resistant to deltamethrin (TsCJB; RR50: 6.50), whereas according to ZERBA & PICOLLO (2002) criterion, the value rises to 55.5%. Qualitative bioassays revealed a DD (diagnostic dose) mortality ranging from 43.3% to 100%, with 61.2% of the population classified as deltamethrin resistant. The results in qualitative and quantitative bioassays were not related, emphasizing the need of field trials. The standardization of biochemical assays showed that these must be performed with insects of the same generation and age, with a sample of 135 specimens. The analysis of biochemical assays using only the 99 percentile proved to be deficient, justifying the need of a parallel statistical test, to be chosen according to the statistical distribution of the results. The analysis of triatomine populations showed alterations in most of them for all the enzymes (alpha-EST, beta-EST, PNPA-EST, OFM and ACHE), except GST. No correlation was found between the RR values and the biochemical tests results. Localities with triatomines classified as resistant or susceptible presented similar patterns when considered: intradomiciliary constitution, types of peridomiciliary ecotopes, availability of hiding places, and use of insecticides by the resident. Only on the Barriguda locality was reported the collecting of firewood in surrounding vegetation by residents. Differences in the climatic variables (solar radiation, temperature and rainfall) were verified throughout the municipality (p <0.05). Premises infestation history and used insecticide charge showed to be higher at Barriguda, Jataí Jataí I and Jataí II. Triatoma sordida was the predominant species captured (94.5%). The municipality of Coração de Jesus currently has three health workers with little time of professional experience, not trained to insecticide spraying activities in accordance to ministry of health recommendations. Microsatellites analysis revealed a high genetic diversity. The FST analysis allowed infer the existence of interchange among insects populations between Jataí I, II Jataí, Boa Vista localities, and an independent isolation of Barriguda and Bom Jesus populations. Considering the stated results, the use of insecticides for various purposes, possible operational failures mainly due the lack of training and supervision of health workers, in combination with insecticide irregular degradation caused by environmental conditions, may contribute for selection of resistant individuals justifying the persistence of infestation in region. The diversity of RR observed within the same locality, the genetic flow observed in molecular assays, the abundance and diversity of hiding places and different biochemical profiles allow to infer that insecticide resistance may be underestimated.