SPATIAL AND TEMPORAL DISTRIBUTION PATTERNS OF DRIFTING PUPAL EXUVIAE OF CHIRONOMDIAE (DIPTERA) IN STREAMS OF TROPICAL NORTHERN AUSTRALIA

1. Periodic collecting of floating cast pupal cuticles of chironomids (exuviae) in two tropical northern Australian streams demonstrates (i) spatial heterogeneity in species composition across a wide stream, (i i) temporal heterogeneity in the maximum abundance of each species, an d that (iii) species accumulate as a function of sample size and durat ion of sampling. 2. Spatial heterogeneity is ascribed to variation in larval microhabitat across the wide stream, combined with short exuvia l drift duration and restricted upstream mixing. 3. Temporal heterogen eity is ascribed to diel periodicity in adult emergence and, as with s patial heterogeneity, to the short floating life. 4. The consequences of spatial and temporal variation for the sampling of exuvial drift ar e discussed in relation to the objectives of particular programmes. Th us, if the objective is assessment of chironomid species composition f or inventory purposes such as faunistics or conservation, the large sa mple sizes attained by 24-h sampling are necessary and appropriate. Ho wever, for rapid assessment that requires comparable samples at differ ent sites, species numbers may be optimized by temporally and spatiall y restricted sampling of the maximal emergence period, which in this s tudy is at dusk, or by subsampling from a 24-h sample.