Interaction characteristics between Triatoma infestans Klug, 1834 and Triatoma sordida Stal, 1859 populations were studied in artificial ecotopes for 16 mo. The experimental design involved simultaneous treatments with T. infestans and T. sordida together in the same experimental unit (EU) and each separately in two control units (CU) made of adobe bricks. Chickens were used as host animals. Each unit was dismantled monthly to estimate triatomine population size and age structure, rebuilt, and repopulated with the same insects. In both units, T. infestans population growth followed a logistic model, whereas T. sordida did not show this pattern. T. infestans completed a generation in 24 wk (EU) and 32 wk (CU1), whereas T. sordida did not complete one generation during this period. We concluded that T infestans showed a better colonizing success than T. sordida. After living together for 1 yr, an interference process took place that resulted in the extinction of T. sordida.