A single village control trial for Triatoma pallidipennis and T. barberi was conducted using three synthetic pyrethroids (bifenthrin, cyfluthrin, and deltamethrin), evaluated as residual treatments in separate sectors, with complete coverage indoors and in peridomiciliary areas. Spray intervention was preceded by a preintervention entomological evaluation and household survey, followed by four postintervention evaluations at 1, 3, 6, and 12 mo of > 96% of houses. Overall preintervention adjusted infestation index was 38%, 17% of which represented intradomicile infestation. Dose verification using high-performance liquid chromatography (HPLC) demonstrated correct spray doses for all but deltamethrin treatments. There was between a 6- and 13-fold decrease in intradomicile live bug infestation for cyfluthrin- and bifenthrin-treated areas, resulting at 1 mo in 0 and 0.6% infestation, respectively. Intradomicile infestation recovered somewhat, terminating at 20 and 50% of preintervention levels at 12 mo, respectively, while peridomicile infestation recovered preintervention levels within 3-6 mo. Households with persistent live peridomiciliary infestation had 1.9 times the risk of having a persistent intradomiciliary infestation, while 80% of peridomicile infestations for both triatomine species were in houses not having a previous infestation. New or reinfestation of households did not occur consistent with a sylvan source, and unconstructed lots were not a significant source of bugs. Houses with persistent peridomicile infestation did represent a significant risk for surrounding uninfested houses by cluster analysis (P < 0.05). Along with the increased prevalence of T. cruzi infection after intervention, the data indicate that a sylvan reservoir source, probably peridomicile small rodent nests, represent the major risk factor for persistent and new infestations.