the values of biological parameters related to hatching, lifespan, the number of blood meals between moults, mortality, time lapse before the beginning of feeding, feeding time and defecation delay for each instar of three mexican-american species of triatominae, triatoma recurva, triatoma protracta (former subspecies protracta) and triatoma rubida (former subspecies uhleri), were evaluated and compared. no significant (p > 0.05) differences were recorded among the three species with respect to the average time required to hatch. this time was approximately 19 days. the average egg-to-adult development time was significantly (p < 0.05) shorter for t. rubida. the number of blood meals at each nymphal instar varied from one-five for each species. the mortality rates were higher for the first-instar nymphs of the three species studied. the mean time lapse before the beginning of feeding was between 0.3-3 min for most nymphs of all instars of each species studied. the mean feeding time was the longest for t. recurva, followed by t. protracta. the defecation delay was less than 10 min for t. recurva and t. rubida. given these results, only t. rubida should be considered an important potential vector of trypanosoma cruzi transmission to humans in areas of mexico where these species exist, whereas t. recurva and t. protracta would be of secondary importance.