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

Abstract

Introduction:Triatoma sordida is the most captured Triatomine species in the Brazilian artifi cial 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 fi rst 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 1xLD 99 of the susceptibility reference lineage. Results: Susceptibility profi le characterization of T. sordida populations revealed resistance ratios (RR 50 s) 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 RR 50 >1.0 have altered susceptibility, and the execution of simultaneous fi eld 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.

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

“…A similar fi nding was reported for Triatoma sordida (23) (24) , which led us to refl ect on the weak criteria recommended by the PAHO 17 for the choice of SRLs: over fi ve generations in the laboratory without insecticide contact, external material contribution, or originating from places that have never been treated with insecticide.…”

“…Importantly, populations from different locations within the same municipality presented different toxicological profi les. This fi nding suggests that the selection process for pesticides can occur independently, even in neighboring houses (22) (23) .…”

History of insecticide resistance of Triatominae vectors

“…As an example, the RR 50 observed by Obara et al (51) for T. sordida populations treated with deltamethrin allowed the study population to be classifi ed as susceptible to the tested insecticide, leading to the recommendation of time line monitoring. However, if the authors had used the SRL adopted by Pessoa (31) , the RR 50 would have increased nine fold. Under this scenario, the populations would have been classifi ed as resistant, and the insecticide used should have been replaced with an insecticide with a different action mode.…”

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

“…In this context, the objective of this study was to determine the mean value of different resistance ratios obtained by laboratory bioassays in the chemical control strategies in the fi eld. We selected populations of T. sordida that had the deltamethrin susceptibility profi les described by Pessoa et al (6) (7) , presenting different RR 50 (1.30-7.01), ( Table 1).…”

“…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 (RR 50 < 8) (3) . (6) . ** Data from Pessoa et al (7) .…”