Invertebrates sample documentation

Freshwater macroinvertebrates were comparatively sensitive to diazinon (Table 16.7). Results of large-scale experimental stream studies (Arthur et al. 1983) showed that dose levels of 0.3 pg diazinon/L caused a five- to eightfold reduction in emergence of mayflies and caddisflies within 3 weeks. After 12 weeks, mayflies, damselflies, caddisflies, and amphipods were absent from benthic samples. Elevated (and catastrophic) drift of stream invertebrates was also documented in diazinon-treated streams, especially for amphipods, leeches, and snails (Arthur et al. 1983). Shortterm tests of 5-h duration with rotifers (Brachionus calyciflorus) show a 50% reduction in feeding... 

Aquatic Invertebrates. The initial impact of insecticides on most benthic invertebrates in streams is the inability to maintain their position on the streambed resulting in increased numbers being carried downstream in what is termed drift. Invertebrate drift in treated streams is easily sampled by holding a net in the current. Post-spray catches can be compared to both pre-spray diurnal patterns and catches at an untreated upstream station or in an untreated control stream. This method also can be used to document knockdown of streamside foliage-dwelling or arboreal insects if the net is set so as to sample the stream s surface. Impacts on stream invertebrates can also be determined by caging studies and by pre- and post-spray bottom fauna population assessments which either sample the numbers within a given area of natural streambed (e.g., Surber sampler) or on artificial substrates intentionally set in the stream before treatment to be colonized by resident populations. 

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