Standardization of laboratory bioassays for the study of Triatoma sordida susceptibility to pyrethroid insecticides

Abstract

BackgroundIncreasing reports of high-resistant Triatominae populations concerns scientists and sanitarians as little is known about the factors behind the occurrence of such phenotype and its real impact on vector control strategies. Moreover, the utilization of a large variety of methodologies hinder the comparison of the reported studies.MethodsThis work aims to review laboratory bioassays, redefining the assessed biological features (age, generation and insecticide application area) and technical procedures (mortality recording time and the ideal diagnostic dose).ResultsResults were not influenced by the insecticide application area in nymphs or by their generation. Three days-old specimen’s revealed lower susceptibility to the tested insecticide. We determined that it is more appropriate to record mortality 72 h after treatment with insecticide, as well as using a diagnostic dose of 1xDL99.ConclusionThis work suggests more adequate methodological parameters for assessing insecticide resistance in triatomines, which also allows the comparison of results obtained by different research groups. For laboratory bioassays, we recommend: 1) the use of first instar nymphs from first or second generation; 2) 3 day-old specimens; 2) application of insecticide in the dorsal or ventral abdomen area; 3) mortality recording 72 h after treatment with pyrethroids and 4) a diagnostic dose of 1x LD99.

Variability of susceptibility to deltamethrin in peridomestic Triatoma sordida from Triângulo Mineiro, State of Minas Gerais, Brazil

“…The susceptibility profi le of T. sordida in our study is similar to that by Obara et al (15) but unlike that by Pessoa et al (13) . However, the different toxicological profi les of deltamethrin in T. sordida populations from distinct locations in the same municipality (e.g., Frutal/Guilherme F. Correa and Frutal/ Aureliano N. Cruz), showed the complexity of the resistance phenotype, at both macro-and microgeographical levels, as observed by Pessoa et al (16) in their studies of Brazilian T. infestans populations from Rio Grande do Sul.…”

“…For each concentration, three repetitions were carried out with ten fi rst instar nymphs of the F1 generation (5 days-old, fasting, weight 1.2 ± 0.2mg). The treatment consisted of the application of 0.2µL of insecticide dilution on the dorsal abdomen by using a Hamilton microsyringe mounted on a repeating dispenser, according to the procedures of the World Health Organization (12) and Pessoa (13) . For each populations, a minimum of eight doses of insecticide active ingredient (a.i.)…”

“…based on the SRL. The survival of at least two insects in three replicates was interpreted as a resistance indicator (12) (13) .…”

“…Despite reports of persistent T. sordida infestation, only two studies have determined the susceptibility of Brazilian populations of this triatomine to insecticides (13) (15) . Pessoa (13) showed the deltamethrin toxicological profile in eleven peridomestic T. sordida populations collected from areas with reports of persistent infestation, in the North of Minas Gerais.…”

“…Pessoa (13) showed the deltamethrin toxicological profile in eleven peridomestic T. sordida populations collected from areas with reports of persistent infestation, in the North of Minas Gerais. The resistance ratios (RR 50 2.6-6.8) in that study were the highest for T. sordida.…”