BACKGROUNDPhysical factors can determine the level of triatomine abundance, but do not regulate their population densities, and neither do natural enemies.OBJECTIVESTo identify the processes associated with density-dependent triatomine population regulation.METHODSWe set-up a laboratory experiment with four interconnected boxes; the central box harboredRhodnius prolixusbugs and one hamster. Stage 5 and adult densities of 10, 20, 30, 40, and 60 bugs per hamster, were replicated four times (except the density of 60 bugs). Hamster’s irritability and several triatomine responses were measured: feeding, development time and longevity, mortality, fecundity, dispersal, and the net reproductive value (Ro).FINDINGSDensity had a statistically significant effect on irritability, but not on the percent of bugs feeding. Density was significant on blood meal size ingested in bugs that did not move between boxes, but not significant when the bugs moved. Density and irritability affected the proportion of stage 5 nymphs molting, and the proportion of adult bugs dying per day and over a three-week period. There was a highly significant effect of density and irritability onRo.MAIN CONCLUSIONSWe showed that a density-dependent mechanism, acting through the irritability of the host, seems the most plausible process regulating populations in triatomines.