Insecticide resistance in Brazilian Triatoma infestans and Venezuelan Rhodnius prolixus

Abstract

Resistance levels to insecticides used in control of Chagas Disease vectors were assessed in two species of bugs (Hemiptera: Reduviidae): Triatoma infestans (Klug) from Brazil and Rhodnius prolixus Stål from Venezuela. The resistance ratios, compared to susceptible laboratory strains, were determined by topical application bioassays. The T. infestans PA strain exhibited resistance ratios of 7x to deltamethrin, 3.6x to beta-cyfluthrin and 3.3x to cypermethrin, but was susceptible to beta-cypermethrin and lambda-cyhalothrin. Rhodnius prolixus CA strain showed resistance to all the pyrethroids evaluated, the resistance ratios ranging between 4.5x to lambda-cyhalothrin and 12.4x to cypermethrin. Deltamethrin resistance in both strains was decreased by piperonyl butoxide, suggesting oxidative metabolism as cause of resistance.

Susceptibility of Triatoma infestans to deltamethrin in Rio Grande do Sul, Brazil

“…The RS populations studied here probably originated from different localities than those investigated by Vassena et al (2000), which would explain the discrepancies between the results of the two studies. On the other hand, the resistance of these populations could also have been eliminated over the years that separated the two sampling periods.…”

“…The first report came from Venezuela in the 1970s, on areas where Rhodnius prolixus was regularly treated with HCB (Rocha & Silva 1979). The first evidence of resistance to synthetic pyrethroids was obtained by the Centro de Investigaciones de Plagas e Insecticidas, in Buenos Aires, in the 1990s (Vassena et al 2000). In this pioneer study, R. prolixus from Venezuela and T. infestans from the Brazilian state of Rio Grande do Sul (RS) were studied, and the authors found resistance ratio (RR) values characteristic of populations already possessing initial resistance.…”

Biology, diversity and strategies for the monitoring and control of triatomines - Chagas disease vectors

“…This can be summed to the control challenges posed by other vectors that are already considered not eliminable due to the large rates of domiciliary infestation promoted by their sylvatic foci, such as T. brasiliensis, Panstrongylus megistus (Burmeister, 1835) and Triatoma dimidiata (Latreille, 1811). This scenario is associated with the fact that some vector species are already present in populations characterised as resistant to insecticides (Vassena et al 2000, Piccolo et al 2005. This process was likely the consequence of the chronic application of insecticides during the past decades.…”

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

“…Several authors have demonstrated that the same triatominic population exhibits different toxicological profi les when exposed to the same chemical class of insecticide (10) . We emphasize that laboratory studies are only indicative of resistance in the fi eld, and they cannot suggest another pyrethroid as a replacement.…”