Triatoma infestans is an insect with a high colonization capacity, capable of maintaining populations near saturation levels in different environments. However, it has a great lability in its population parameters when exposed to variable environmental conditions. The aim of this work was to explore the response of two cohorts with 4 initial egg densities, in two environmental conditions ("shelter" at 24 +/- 2.7 degrees C and 73 +/- 7% of relative humidity and "room" at 16.9 +/- 2.1 degrees C and 69.8 +/- 5% of relative humidity), similar to those commonly found in houses at Santiago, Chile. The proportion of fertile egg was higher in shelter conditions (93.7 vs 74.6%). Survival curves were similar in both environments and mortality was not influenced by density or maturity of individuals. Maturation was retarded in both environment, specially in the colder one, compared to constant environments. It is concluded that maturation of T infestans is the most affected parameter in the unprotected environment. Even though, considering the insect's longevity, its reproductive function is probably accomplished. The great lability of T. infestans population parameters, suggests that the finding of favorable microenvironments is essential for their survival.