Spatio-temporal dynamics of deltamethrin resistance in Triatoma infestans: Challenges for chagas disease vector...

The emergence of insecticide resistance in Triatoma infestans, driven by extensive pyrethroid use, represents a major obstacle to effective Chagas disease vector control in Argentina. Given the spread of resistance and the impact on control efforts, understanding its geographical and temporal patterns is crucial for guiding resilient and effective intervention efforts. This study presents a spatio-temporal analysis of deltamethrin resistance across nine Argentine provinces during 2013-2023 period, based on biotoxicological assays of T. infestans populations collected from 155 locations, complemented by historical resistance data from the literature and analysis of insecticide application. Resistance levels were classified as low, medium, or high based on resistance ratios calculated from DL₅₀ values. Results show that 46.45 % of the populations analyzed were resistant to deltamethrin, with resistant populations found in five provinces, indicating a notable geographic expansion into new ecoregions. We report the first widespread emergence of medium resistance levels (10 < RR₅₀ < 100) in four provinces, alongside geographic expansion into new ecoregions, highlighting an active process of resistance evolution with notable regional variability. Combining resistance data with insecticide application we observed three distinct resistance patterns in vector populations: stable susceptible, stable resistance, and variable resistance levels over time. Our findings suggest that conventional pyrethroid treatments may be insufficient, especially in high-resistance regions. This study underscores the need for adaptive, region-specific management approaches and the integration of continuous monitoring efforts, as initiated by Argentina's National Pesticide Resistance Surveillance Network (RAReP). These efforts are essential for enhancing vector control efficacy and mitigating the spread of Chagas disease.