Particle Size and Chironomid (Diptera) Food in an Upland River

The food ingested by a number of chironomid species in a stony-bottom stream was examined. Temporally co-occurring species ingested closely similar food types and sizes, but considerable differences were found between species having different phenologies. Furthermore, different larval instars of Cricotopus trifascia Edw. fed on different food particle types and sizes, smaller larvae consuming, on average, smaller particles than larger larvae. This tendency recurred when comparing larvae of different sizes belonging to different species. Field and laboratory studies showed that larvae tend to ingest particles in the proportions available in the environment and that populations apparently were food-limited. The amount and size distribution of food particles therefore strongly affect the distribution of stream-living chironomids in space and time.