The long-term dynamics of freshwater insect populations have attracted little interest. The aim of this study was to examine the recruitment, larval mortality and reproductive output of the bivoltine caddisfly, Tasimia palpata (Tasimiidae). Ten consecutive generations were monitored to determine which life-history phases were density dependent. If direct density dependence occurs, mortality during a phase of the life cycle should be positively correlated with the density of individuals entering that phase. Quantitative samples were taken from April 2004 to March 2009 along a 190m reach. The relationship between the number of recruits (R1) and egg density (S) was modelled using a Ricker stock-recruitment curve. In this model, ln (S/R1), a measure of mortality, is a linear function of S. The Ricker curve for T. palpata was an excellent fit and mortality was strongly correlated with S (r = 0.96, p = 0.03). Population regulation thus occurred during recruitment. Further analysis showed that it also occurred during pupation but not during the larval phase of the life cycle. Seasonal variations in water temperature and discharge did not influence mortality. The population was considered closed (i.e.no migration) despite exposure to floods and proximity to the sea (< 1km to estuary).