Peritrich ciliates epizoic on larvae of Brachycentrus subnubilus (Trichoptera): importance in relation to the total protozoan population in streams

Abstract

The numerical abundance of peritrich ciliates epizoic on larvae of Brachycentrus subnubilus in an English chalk stream is described for an 18-month period. Peaks in the epizoic population occurred during winter at a time when protozoan populations in other stream habitats were low. Ciliates were absent from the first three instars of their host, but were abundant on fourth and fifth instar larvae. Estimates of generation times in the field were made for the ciliate populations (January – February 186 h; July – August 471 h). The relative importance of the epizoic ciliate population as a whole is considered in relation to other protozoan populations in the streams.