Effects of 2,4-dichlorophenol on the net-spinning behavior of Hydropsyche slossonae larvae (Trichoptera; Hydropsychidae), an early warning signal of chronic toxicity

In order to assess the potential of hydropsychid capture net anomalies as a bioindicator of chronic toxicity in streams and rivers, the effects of 2,4 -dichlorophenol (2,4-DCP) exposure on the net-spinning behavior of Hydropsy che slossonae were examined for anomalies after 0, 5, 10, 15, and 20 exposu re days to gradient concentration of 2,4-dichlorophenol, The net-spinning b ehavior was significantly affected when larvae mere exposed to 1.0, 10, 25, and 50 mu g.L-1, as expressed by the occurrence of two distinct abnormalit ies. The first one was a distortion of the midline meshes, where the normal diamond-shape structure is disrupted and the meshes are separated by extra strands (called "midline" anomaly). The second aberration observed was cal led "chaotic" net, where the nets are highly irregular without any real str ucture or well-defined areas. ii good correlation was found between the cha otic net frequencies and the reduction of ATP concentrations in the larvae, indicating possible uncoupling effects of 2,4-DCP on the oxidative phospho rylation process. Toxicity curves demonstrate that the sensitivity threshol d of chaotic net frequencies ranged from 3.5 to 7 mu g.L-1, which is highly sensitive compared with other sublethal effects of 2,4-DCP on other aquati c species. (C) 2000 Academic Press.