ECOLOGY OF LEPTOCERID CADDISFLY LARVAE IN AN INTERMITTENT SOUTH AUSTRALIAN STREAM RECEIVING EUCALYPTUS LITTER

1. Brown Hill Creek, a small intermittent stream in dry sclerophyll forest in South Australia, flows for about 6 months during winter and spring. When flow ceases the stream dries to isolated pools which receive high summer inputs of Eucalyptus obliqua litter. Decomposition of this material in remnant pools causes extremely dark waters and depressed oxygen concentrations for up to 90 days. 2. Only two fully aquatic insect species, Leptorussa darlingtoni and Lectrides varians (Trichoptera: Leptoceridae), persist under these conditions. Both utilize litter as food, but have different feeding strategies. The more abundant L. darlingtoni ingests organic and microbial material from leaf surfaces, whereas L. varians is a leaf shredder. 3. Larval processing budgets based on laboratory and field experiments indicated that L. varians has a greater impact on litter decomposition rates than L. darlingtoni. However, because of low density, low oxygen concentrations in pools during summer, and rapid flushing of litter from pools once flow recommences, L. varians larvae process a small proportion of the total litter input.