Insect drift in Condor Creek, Australian Capital Territory

Abstract

Samples of benthos and drift were taken in the same locality in March, April, June and July 1978. Most species appeared in both benthos and drift. The benthos was dominated by Atalophlebioides sp. (Ephemeroptera) and Helicopsyche sp. (Trichoptera) in April and June, plus Glossosomatinae (Trichoptera) in July. The principal taxa occurring in the drift were Leptoceridae sp. 1 (27%), Atalophlebioides sp. (15%), Chironomidae pupae (8%), Leptoceridae sp. 2 (6%) and Chironomidae larvae (5.473. A major spate in May caused changes in the proportions of the benthic and drifting fauna, probably due to the differential effect of scouring on different behavioural strategies.

Drift rate varied temporally (nocturnal maximum) and with creek discharge. High numbers of caseless larvae of some Trichoptera in the nocturnal drift are believed to be indicative of case-building activity. Incidental evidence is provided to support the hypothesis of previous authors that moonlight depresses drift rates. Mean diel drift rates for 24 taxa are given. Ephemeroptera and Trichoptera were more prevalent at night and Chironomidae pupae during the day. The Ephemeroptera larvae drifting during the day were, on average, smaller than those drifting at night.