On the basis of their ecological behavior the triatomines are distributed into six groups: 1. Typically wild insects, i. e., species that are found only in natural ecotopes, never being collected in human dweellings and their annexes. Consequently they never come into contact with man and domestic, commensal or synantropic mammals, unless they enter the natural foci. But these insects may have a more or less important role in maintaining the wild trypanosome enzooty. Examples: Psammolestes coreodes, Psammolestes tertius, Cavernicola pilosa, Triatoma dispar, Triatoma delpontei and other little known species. 2. Essentially wild insects whose adults occasionally invade human dwellings and their annexes but are unable to thrive in artificial ecotopes. In addition to the role in the wild cycle of transmission of T.cruzi, they may come into contact with man and domestic or domiciliated mammals and transmit the infection both in natural foci and artificial ecotopes. Examples: Panstrongylus geniculatus, Triatoma rubrovaria, Triatoma arthurneivai, Triatoma patagonica, Triatoma eratyrusiforme, Rhodnius domesticus, etc. 3. Wild insects beginning to adapt to artificial ecotopes where they give rise to small colonies specially in animal dens, and, more rarely, inside human dwellings. In addition to the role in the wild cycle of transmission of T.cruzi, they may convey the parasite from natural to artificial ecotopes and, under certains circunstances, participate of the domiciliary cycle of T.cruzi. Examples: Rhodnius neglectus, Triatoma vitticeps, Triatoma platensis, etc. 4. Insects that breed indifferently in natural or artificial ecotopes. Although they havesuccededinadaptingthemselves to human dwellings and domestic animal dens, they are also found in many natural ecotopes. In addition to the role in the wild transmission cycle of T.cruzi they are important in the conveyance of the parasite frotn natural foci to artificial ecotopes and in the inicial infestation or in the reinfestation of these ecotopes, and are an efficient ring in the domiciliary chain of transmission of T.cruzi. Examples: Panstrongylus megistus, Rhodnius prolixus, Rhodnius pallescens, Triatoma sórdida, Triatoma brasiliensis, Triatoma pseudomaculata, Triatoma quasayana etc. 5. Insects well adapted to artificial ecotopes, but sometimes still found in residual natural breeding places. They are most important in the domiciliary cycle of transmission of T.cruzi, but may play, at least in certain areas, a small role in the wild cyde of transmission of the infection. Example: Triatoma infestans. 6. Entirely domiciliated insects. In spite ofbeing found only in houses, they seem to have a minor role in the transmission of T.cruzi to man, because they live more into contact with commensal rats, aithough thay may also bite man. Example: Triatoma rubrofasciata.