Toxicological, Enzymatic, and Molecular Assessment of the Insecticide Susceptibility Profile ofTriatoma infestans(Hemiptera: Reduviidae, Triatominae) Populations From Rural Communities of Santa Cruz, Bolivia

Abstract

A wide range of insecticide resistance profiles has been reported across Bolivian domestic and sylvatic populations of Triatoma infestans (Klug, 1834) (Hemiptera, Reduviidae), including some with levels proven to be a threat for vector control. In this work, the insecticide profile of domestic T. infestans was studied with standardized toxicological bioassays, in an area that has not undergone consistent vector control. F1 first-instarnymphs hatched in laboratory from bugs captured in three communities from the Santa Cruz Department were evaluated with different insecticides. Moreover, the enzymatic activity of esterases and cytochrome P450 monooxygenases was measured in individual insects to evaluate the possible mechanism of metabolic resistance to pyrethroids. In addition, the DNA sequence of sodium channel gene (kdr) was screened for two point mutations associated with pyrethroid resistance previously reported in T. infestans. All populations showed reduced susceptibility to deltamethrin and α-cypermethrin, albeit the RR50 values varied significantly among them. Increased P450 monooxygenases and permethrate esterases suggest the contribution, as detoxifying mechanisms, to the observed resistance to deltamethrin in all studied populations. No individuals presented either mutation associated to resistance in the kdr gene. The level of susceptibility to α-cypermethrin, the insecticide used by the local vector control program, falls within an acceptable range to continue its use in these populations. However, the observed RR50 values evidence the possibility of selection for resistance to pyrethroids, especially to deltamethrin. Consequently, the use of pyrethroid insecticides should be closely monitored in these communities, which should be kept under entomological surveillance and sustained interventions.

NovelKdrmutations (K964R and A943V) in pyrethroid‐resistant populations ofTriatoma mazzottiiandTriatoma longipennisfrom Mexico and detoxifying enzymes

“…The results obtained in the bioassays were subjected to probit analysis using POLO Plus Version 1 (LeOra Software 2002-2017 to estimate the lethal dose to kill 50% of the population (LD 50 ). The significant difference between the LD 50 parameters was determined by the overlap of the confidence intervals (Santo-Orihuela et al, 2017). Zerba and Picollo (2002) and D'Ávila Pessoa et al (2014) criteria were used to consider insecticide resistance.…”

Indoor residual spraying practises against Triatoma infestans in the Bolivian Chaco: contributing factors to suboptimal insecticide delivery to treated households

“…Vectorial transmission is considered the main route of infection in these communities, the predominant vector being Tri. infestans which colonises houses and outbuildings [19, 20].…”

“…infestans [11, 19], and 40%-56% of Tri. infestans are infected with T. cruzi [20, 21]. The majority (>93%) of all vectorial transmitted Chagas disease cases in the Southern Cone region occur in Bolivia [5].…”

“…Factors affecting IRS effectiveness, and the persistence of vectorial transmission in the Grand Chaco region, is variably attributed to poor building construction [17, 19], suboptimal IRS implementation practices and infestation surveillance methods [28], low public compliance to IRS requirements [29], short residuality of insecticide formulations [30, 31], and to Tri. infestans resistance and/or reduced susceptibility to insecticides [20, 32].…”

“Genetic structure and sodium channel gene mutation analysis related to pyrethroid insecticide toxicity in sylvatic Andean Triatoma infestans from Bolivia”

“…A fragment of the DNA sequence of the sodium channel gene was amplified and screened for two nucleotide mutations previously reported in T. infestans associated with pyrethroid knockdown resistance ( kdr ) [63, 64]. The protocol has been previously described [65] and was used to screen 67 individuals from the five populations (Table 1).…”