Chagas' disease is an important public health concern in Latin America. Despite intensive vector control efforts using pyrethroid insecticides, the elimination of Triatoma infestans has failed in the Gran Chaco, an ecoregion that extends over Argentina, Paraguay, Bolivia and Brazil. The voltage-gated sodium channel is the target site of pyrethroid insecticides. Point mutations in domain II region of the channel have been implicated in pyrethroid resistance of several insect species. In the present paper, we identify L925I, a new pyrethroid resistance-conferring mutation in T. infestans. This mutation has been found only in hemipterans. In T. infestans, L925I mutation occurs in a resistant population from the Gran Chaco region and is associated with inefficiency in the control campaigns. We also describe a method to detect L925I mutation in individuals from the field. The findings have important implications in the implementation of strategies for resistance management and in the rational design of campaigns for the control of Chagas' disease transmission. One of the principal goals of the Southern Cone Initiative (SCI), created in 1991, is to reduce the geographic range and infestation prevalence of triatomines, vectors of Chagas'disease. Despite its success in many areas, the elimination of Triatoma infestans has failed in the Gran Chaco ecoregion, even in areas subjected to intense vector control efforts with pyrethroid insecticides. Detecting the reasons for the persistence of T. infestans in the Gran Chaco has been recognized as a priority of the SCI, in its 15^th meeting held in Brasilia in 2006. The voltage -dependent sodium channel is the target protein of pyrethroid insecticides. In this work, we investigated possible mutations in the sodium channel gene in a highly resistant population from Gran Chaco. We found a point mutation that affects the structure of the channel and is associated with high resistance to pyrethroids. We also present a simple and low-cost method to detect this mutation in individuals from the field. Our results are important for monitoring the presence and spread of pyrethroid-resistant populations of T. infestans, a critical requirement in the implementation of strategies for resistance management and for the rational design of campaigns oriented to controlling the transmission of Chagas' disease.

Triatomine insects are vectors of Trypanosoma cruzi, a protozoan parasite that is the causative agent of Chagas’ disease. This is a neglected disease affecting approximately 8 million people in Latin America. The existence of diverse pyrethroid resistant populations of at least two species demonstrates the potential of triatomines to develop high levels of insecticide resistance. Therefore, the incorporation of strategies for resistance management is a main concern for vector control programs. Three enzymatic superfamilies are thought to mediate xenobiotic detoxification and resistance: Glutathione Transferases (GSTs), Cytochromes P450 (CYPs) and Carboxyl/Cholinesterases (CCEs). Improving our knowledge of key triatomine detoxification enzymes will strengthen our understanding of insecticide resistance processes in vectors of Chagas’ disease. The discovery and description of detoxification gene superfamilies in normalized transcriptomes of three triatomine species: Triatoma dimidiata, Triatoma infestans and Triatoma pallidipennis is presented. Furthermore, a comparative analysis of these superfamilies among the triatomine transcriptomes and the genome of Rhodnius prolixus, also a triatomine vector of Chagas’ disease, and other well-studied insect genomes was performed. The expression pattern of detoxification genes in R. prolixus transcriptomes from key organs was analyzed. The comparisons reveal gene expansions in Sigma class GSTs, CYP3 in CYP superfamily and clade E in CCE superfamily. Moreover, several CYP families identified in these triatomines have not yet been described in other insects. Conversely, several groups of insecticide resistance related enzymes within each enzyme superfamily are reduced or lacking in triatomines. Furthermore, our qRT-PCR results showed an increase in the expression of a CYP4 gene in a T. infestans population resistant to pyrethroids. These results could point to an involvement of metabolic detoxification mechanisms on the high levels of pyrethroid resistance detected in triatomines from the Gran Chaco ecoregion. Our results help to elucidate the potential insecticide resistance mechanisms in vectors of Chagas’ disease and provide new relevant information for this field. This study shows that metabolic resistance might be a contributing cause of the high pyrethroid resistance observed in wild T. infestans populations from the Gran Chaco ecoregion, area in which although subjected to intense pyrethroid treatments, vector control has failed. This study opens new avenues for further functional studies on triatomine detoxification mechanisms. One of the principal goals of the last decades regarding public health in Latin America was the reduction of the geographic range and infestation rates of triatomines, the insect vectors of Chagas’ disease. However, the elimination of vector transmission has failed in the Gran Chaco ecoregion, even in areas subjected to intense vector control efforts with pyrethroid insecticides. Therefore, detecting the reasons for the persistence of these vectors has been recognized as a priority by public health authorities. Metabolic insecticide resistance due to enhancement of detoxification activity is one of the principal resistance mechanisms observed in insects. In this study, we analyzed the main enzyme superfamilies known to be involved in insecticide resistance in other insects in four important Chagas’ disease vector species from different regions of Latin America. This was made in a comparative manner using well-studied insect genomes as references. We have found gene expansions for several families related to insecticide resistance, while others showed a reduction. Augmented expression of a CYP gene may suggest contribution to pyrethroid resistance in highly resistant populations of Triatoma infestans from the Gran Chaco. Our results increase the knowledge of potential insecticide resistance mechanisms in vectors of Chagas’ disease and provide relevant information to this field.