Consequences of Removal of Pupae for a Population of Potamophylax cingulatus (Trichoptera) in a South Swedish Stream

All pupae of Potamophylax cingulatus (Steph.) were removed from the uppermost 1.6 km of a South Swedish stream. The next initial larval population had dwindled by about half in relation to the prior season suggesting that, under undisturbed conditions, immigrant females in this case would have been responsible for about half of the recruitment. However, the larval population, presumably owing to its reduced density, survived so well that the pupal population was 83 % of the previous average. The number of females locally emerged is in normal years enough to provide the major part of the number of pupae in the following generation. However, in order to persist, this population may need a certain immigration of mature females from downstream or from other streams.