Abstract
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. 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. Mortality was 100.0% in all locations, except for Monte Azul; Landinho (96.6%) and Coração de Jesus; Barriguda (96.6%). 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.
Highlights
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
As for Brazilian triatomines, investigative studies on the susceptibility to insecticide are on the rise and have focused on Triatoma brasiliensis, Triatoma sordida, Panstrongylus megistus, and T. infestans collected in areas with reports of persistent triatominic infestations (RR50 < 8)(3)
By using the criterion recommended by World Health Organization (WHO)(10), all populations were considered susceptible to alpha-cypermethrin
Summary
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. Conclusions: 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. Insecticide resistance results in a decrease in the mortality observed in a population subjected to continuous treatment This characteristic is expressed by a greater number of specimens that tolerate lethal doses compared with specimens considered sensitive during the initial application of the product, leading to selection pressure in populations. As for Brazilian triatomines, investigative studies on the susceptibility to insecticide are on the rise and have focused on Triatoma brasiliensis, Triatoma sordida, Panstrongylus megistus, and T. infestans collected in areas with reports of persistent triatominic infestations (RR50 < 8)(3)
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