AbstractThe effect of the shredderKlapopteryx kuscheli(Plecoptera, Austroperlidae) on the breakdown ofNothofagus pumilioleaves was studied in field experiments. Decay rates due to leaching and shredder activity were measured on conditioned and unconditioned leaves. Two sizes of shredder were tested in order to establish if the consumption per unit of shredder biomass varied with insect development. In three days weight losses due to leaching were 8.5%, and decay rates due to shredders were significantly higher than in control replicates. There were no differences in decay rates between conditioned and unconditioned leaves. Small larvae consumed more leaf biomass per unit of insect biomass than large ones. Growth efficiencies ofK. kuschelilarva were low, but smaller larvae showed higher efficiencies than larger ones.