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Objective To define the insecticide resistance status of Triatoma infestans to deltamethrin (pyrethroid), malathion (organophosphate) and bendiocarb (carbamate) in Bolivia. Methods Fifty populations of T. infestans were sampled in Bolivian human dwellings. Quantal response data were obtained by topical applications of 0.2 μl of insecticide–acetone solutions on nymphs N1 of the F1 generations. For most populations, dose–mortality relationships and resistance ratios (RR) were analysed. Discriminating concentrations were established for each insecticide with a susceptible reference strain and used on the other field populations. A tarsal-contact diagnostic test using insecticide impregnated papers was designed to rapidly identify deltamethrin-resistant populations in the field. Results Discriminating concentrations for topical applications were 5, 70 and 120 ng active ingredient per insect for deltamethrin, bendiocarb and malathion, respectively. The diagnostic concentration for deltamethrin was 0.30% for the 1-h exposure by tarsal contact. All populations sampled in human dwellings exhibited significant levels of resistance to deltamethrin, from 6 to 491 and varied among regions. Resistant populations did not recover complete susceptibility to deltamethrin when the synergist piperonyl butoxide (PBO) was used. None of the sampled populations exhibited significant resistance to bendiocarb (all RR50 0 or <100% mortality were used. For each experiment, a control group received only acetone. Treated and control insects were maintained in a climatic chamber (Sanyo MLR 351-H, Japan) under controlled conditions of temperature (27 ± 1 °C), relative humidity (60 ± 5% RH) and photoperiod 12:12 h (light:dark). Mortality was recorded at 24 h. The criterion for mortality was the inability of the nymphs to walk out of a filter paper disc of 7 cm diameter (Vassena et al. 2000; Picollo et al. 2005). Probit analysis (Finney 1971) was performed on mortality data using probit ver.2 software (Raymond et al. 1993). When results exhibited a large Chi-squared for the Log-probit lines (which was the case for only the El Chaco population for deltamethrin and San Francisco del Inti population for bendiocarb) and because there was no sign of systematic deviation from linear regression, the heterogeneity factor H (Finney 1971) was computed to continue the computations. Resistance ratios (RR) were computed relative to the susceptible reference strain CIPEIN as . When lines were parallel, RRs were computed at LD50 (i.e. RR50) (Finney 1971) and in addition, at LD90 (i.e. RR90) when probit lines were not parallel (Robertson et al. 2007). A dose of 1000 ng active ingredient (a.i.) per insect PBO (Vassena et al. 2000) in 0.2 μl acetone solution was first topically applied on the dorsal surface of the abdomen of N1. Insects were then left 1 h before being processed for topical application of insecticide as explained above. Then, RRs were computed relative to the reference strain CIPEIN, and the percentage of effective reduction in RR50 (with and without PBO) was computed as: If the only mechanism of resistance is based on detoxifying enzymes such as oxidases (cytochrome P450), Preduc% would be expected to be 100% (i.e. a complete recovery of susceptibility to deltamethrin) as RR50 with PBO would be 1. If Preduc% is significantly different from 0% (i.e. it exists some synergistic effect with PBO) but also significantly different from 100% (i.e. the population does not recover total susceptibility to insecticide with PBO), then in addition to detoxifying oxidases, others types of resistance are likely to be The in reduction of RRs was by the of the population and application of PBO without with Preduc% was considered as not significantly different from the one was the of For a the diagnostic concentration is the concentration that 100% mortality of of the susceptible strain (WHO At a diagnostic the Health Organization for resistance is 80% mortality et al. 2008; et al. 2008; Segura et al. and this also for the observed in resistance Because there is no resistance to bendiocarb and malathion by diagnostic dose of insecticide for is to in T. infestans & because these enzymes are for deltamethrin-resistant T. infestans populations in Bolivia, also be for various RR50 1 only to the would be In addition to the resistance mechanism is in insect species resistant to of of pointed in the to and with & Because the tested populations of T. infestans did not recover total susceptibility to deltamethrin with PBO (and in some cases, PBO did not have any and because are the most mechanism is the mechanism which has been by Orihuela et al. for T. infestans populations of Argentina. In with insecticide resistance reports in Argentina, results also the of the of insecticide resistance in the populations of T. the other populations of T. infestans of and from some regions of Argentina to be susceptible to pyrethroids despite the insecticide The of T. infestans populations and has long been et al. 2007), and in of the have been al. populations of T. infestans from Bolivia to have the to insecticide resistance than populations. and insecticide resistance data resistance Resistance of T. infestans be more and than the various insecticide and of the populations. A of be a short-term solution to insecticide resistance Because results that there was no resistance to this could be as a short-term alternative resistance to deltamethrin is In that a should be carried out in areas a vector, also occurs in et al. and is controlled by the Bolivian Ministry of Health with insecticide indoor control strategies integrated are to the resistance of T. and using (WHO 2002, et al. 2007) are The of using organophosphates et al. is but different at the or of organophosphates or carbamates with pyrethroids and the search for insecticide would also be of pyrethroid susceptibility using of other insecticides et al. 2007) could also be strategies using as are et al. but more is to the personnel of the of La Chuquisaca and Tarija Departments as well as the National Program for Control of Chagas Disease of Bolivia for in and the T. infestans populations. are to for the and it. This received from the for and in The that have no of
Lardeux et al. (Wed,) studied this question.