Susceptibility to deltamethrin of wild and domestic populations of Triatoma infestans of the Gran Chaco and the Inter-Andean Valleys of Bolivia

Abstract

Background: The persistence of Triatoma infestans and the continuous transmission of Trypanosoma cruzi in the Inter-Andean Valleys and in the Gran Chaco of Bolivia are of great significance. Coincidentally, it is in these regions the reach of the vector control strategies is limited, and reports of T. infestans resistance to insecticides, including in wild populations, have been issued. This study aims to characterize the susceptibility to deltamethrin of wild and domestic populations of T. infestans from Bolivia, in order to better understand the extent of this relevant problem. Methods: Susceptibility to deltamethrin was assessed in nine, wild and domestic, populations of T. infestans from the Gran Chaco and the Inter-Andean Valleys of Bolivia. Serial dilutions of deltamethrin in acetone (0.2 μL) were topically applied in first instar nymphs (F1, five days old, fasting, weight 1.2 ± 0.2 mg). Dose response results were analyzed with PROBIT version 2, determining the lethal doses, slope and resistance ratios (RR). Qualitative tests were also performed. Results: Three wild T. infestans dark morph samples of Chaco from the Santa Cruz Department were susceptible to deltamethrin with RR 50 of <2, and 100% mortality to the diagnostic dose (DD); however, two domestic populations from the same region were less susceptible than the susceptibility reference lineage (RR 50 of 4.21 and 5.04 respectively and 93% DD). The domestic population of Villa Montes from the Chaco of the Tarija Department presented high levels of resistance (RR 50 of 129.12 and 0% DD). Moreover, the domestic populations from the Valleys of the Cochabamba Department presented resistance (RR 50 of 8.49 and 62% DD), the wild populations were less susceptible than SRL and T. infestans dark morph populations (RR 50 < 5). Conclusion: The elimination of T. infestans with pyrethroid insecticides in Brazil, Uruguay, Chile, and its drastic reduction in large parts of Paraguay and Argentina, clearly indicates that pyrethroid resistance was very uncommon in non-Andean regions. The pyrethroid susceptibility of non-Andean T. infestans dark morph population, and the resistance towards it, of Andean T. infestans wild and domestic populations, indicates that the Andean populations from Bolivia are less susceptible.

Insecticide resistance in vector Chagas disease: Evolution, mechanisms and management

“…This suggests that Andean populations have particular genetic backgrounds that enable the development of resistance to pyrethroid insecticides more rapidly than non-Andean populations. This is in according with Roca-Acevedo et al (2011), Depickere et al (2012, and Gomez et al (2014) who showed varying degrees of tolerance to deltamethrin and fipronil in the sylvatic T. infestans from Andean valleys of Bolivia. However, as has been seen in this review, the resistance to pyrethroid insecticides evolved in the Argentinean Chaco (i.e.…”

“…Depeckire et al (2012) reported resistance to deltamethirn in five localities of Department of Santa Cruz (Estancia Bacilio, Kuatrienda, San Silvestre, Rancho Nuevo and Tamachindi, RRs from 3.8 to 8.3) and one locality of Villamontes, Department of Tarija (Taiguati, RR = 818). Recently, high resistance to deltamethrin was reported again in Villamontes (RR=129.1) and low resistance in Departments of Cochabamba and Santa Cruz (RR from 4.2 to 8.5) (Gomez et al, 2014). All studies cited above showed the highest levels of resistance to pyrethroid insecticides in southern Bolivia, in the Department of Tarija.…”

“…Effectively, the resistance to pyrethroids in T. infestans has been detected in several areas of the geographical distribution of the species, spaced from a few tens of kilometers to over a thousand kilometers across two countries, Argentina and Bolivia (Picollo et al, 2005;Santo Orihuela et al, 2008;Toloza et al, 2008;Lardeaux et al, 2010;Germano et al, 2010bGermano et al, , 2012Germano et al, , 2013Germano et al, , 2014Roca Acevedo et al, 2013;Depickere et al, 2012;Gomez et al, 2014) (Fig 1). T infestans resistant to pyrethroids was reported in the Bolivian Andean Valleys (Departments of Cochabamba, Chuquisaca and La Paz), Bolivian Chaco (Departments of Tarija and Santa Cruz), and Argentinean Chaco (Provinces of Salta and Chaco).…”

History of insecticide resistance of Triatominae vectors

“…The meeting of fi eld populations more susceptible than the SRL (25) (28) (30) (33) reveal the fragility of this criteria.…”

“…The populations that were indicative of resistance were subjected to dose response trials, revealing wide variation in susceptibility (RR 50 3.8-818.0). Gomez et al (30) assessed the susceptibility of 9 populations from Gran Chaco and the Inter-Andean valleys of Bolivia (5 wild populations and 4 domestic populations) to deltamethrin. The wild populations showed low variation in susceptibility (RR 50 0.62-4.24), whereas wide variation in susceptibility was detected for the domestic populations (RR 50 2.9-129.1).…”