Susceptibility to deltamethrin of wild and domestic populations of Triatoma infestans of the Gran Chaco and the Inter-Andean Valleys of Bolivia.
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 RR50 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 (RR50 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 (RR50 of 129.12 and 0% DD). Moreover, the domestic populations from the Valleys of the Cochabamba Department presented resistance (RR50 of 8.49 and 62% DD), the wild populations were less susceptible than SRL and T. infestans dark morph populations (RR50 < 5).


CONCLUSIONS
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.
Laboratório de Triatomíneos e Epidemiologia da Doença de Chagas, Centro de Pesquisas René Rachou - FIOCRUZ Minas, Belo Horizonte, Brazil. marinelybustamante@gmail.com.
Marinely Bustamante
MB
Gomez
Laboratório de Triatomíneos e Epidemiologia da Doença de Chagas, Centro de Pesquisas René Rachou - FIOCRUZ Minas, Belo Horizonte, Brazil. grasielle@cpqrr.fiocruz.br.
Grasielle Caldas Pessoa
GC
D'Avila
Instituto de Investigaciones Biomédicas - Facultad de Medicina, Universidad Mayor de San Simón, Cochabamba, Bolivia. lineth.garcia@gmail.com.
Ana Lineth Garcia
AL
Orellana
CEADES Salud y Medio Ambiente, Cochabamba, Bolivia. mirkorcortez@gmail.com.
Mirko Rojas
MR
Cortez
Laboratório de Triatomíneos e Epidemiologia da Doença de Chagas, Centro de Pesquisas René Rachou - FIOCRUZ Minas, Belo Horizonte, Brazil. aline.rosa@cpqrr.fiocruz.br.
Aline Cristine Luiz
AC
Rosa
Institute de Recherche pour le Developemente (IRD), La Paz, Bolivia. diotaiut@cpqrr.fiocruz.br.
François
F
Noireau
Laboratório de Triatomíneos e Epidemiologia da Doença de Chagas, Centro de Pesquisas René Rachou - FIOCRUZ Minas, Belo Horizonte, Brazil. diotaiut@cpqrr.fiocruz.br.
Liléia Gonçalves
LG
Diotaiuti
D000818:Animals; D001838:Bolivia; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology*; D009570:Nitriles / Q000494:pharmacology*; D021261:Parasitic Sensitivity Tests; D011722:Pyrethrins / Q000494:pharmacology*; D014224:Triatoma / Q000187:drug effects*; D014349:Trypanosoma cruzi
D007306:Insecticides; D009570:Nitriles; D011722:Pyrethrins; C017180:decamethrin