Age structure and colonizatiion of natural substrata by the epilithic caddisfly Tinodes rostocki (Trichoptera: Psychomyiidae)

Tinodes rostocki is a dominant trichopteran species in the Breitenbach, a first-order stream in Central Europe. In the lower reaches, stones were densely covered with larval galleries. Larval development took one year. Between October and May, mean ( ± S.D.) larval densities decreased from 3,100 ± 548 larvae/m² to 762 ± 226, while biomass (DW) increased from 405 ± 104 mg/m² (October) to 801 ± 196 (May). This study investigated whether the larval age structure on undisturbed stones differed from that on stones whose natural population had been removed three weeks earlier, and whether the distance of stones manipulated in this way from unmanipulated stones could influence the recolonization density. In September 1987, six stones from mid-stream were cleared of larvae, marked, and replaced into their original positions. Three stones were placed directly adjacent to colonized stones, while three others were placed at least 30 cm away from colonized stones. The manipulated stones and an unmanipulated control stone were brushed every three weeks to determine larval densities and the age structure. The manipulated stones were recolonized during each sampling interval, but always at lower densities than the control