Anomalies on capture nets of Hydropsyche slossonae larvae (Trichoptera; Hydropsychidae), a potential indicator of chronic toxicity of malathion (organophosphate insecticide)

A laboratory study on the sublethal effects of malathion on the net-spinnin g behavior of the caddisfly larvae Hydropsyche slossonae was conducted in o rder to assess thr potential of net anomalies as an indicator of chronic ex posure to organophosphorus insecticides. Two anomalies were identified afte r chronic exposure to 0.01, 0.05, 0.1, 0.5 and 1.0 mu g l(-1) malathion. Th e first was a distortion of the midline meshes where the normal diamond sha pe structure was disrupted and the meshes were separated by extra strands ( called 'midline' anomaly). The second aberration observed was a significant decrease in net symmetry. Both anomalies were highly correlated to the tox ic action of malathion, i.e. inhibition of the acetylcholinesterase enzyme (AChE). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analyses of capture nets did not show any modification of silk polypeptides after ex posure to malathion, indicating that net distortions: were not related to s ilk composition. Both anomalies seem to represent the symptoms of the specific toxic action of malathion; nevertheless, they can serve as an index of the physiological condition of the larvae. especially the midline anomaly. The symmetry of t he nets decreased significantly after exposure to 0.5 and 1.0 mu g l(-1). H owever, the toxicity curves (EC50) showed that the sensitivity threshold fo r the midline anomaly ranged from 0.11 to 0.28 mu g l(-1) which reflect mor e realistic exposure to concentrations expected to occur in the field. Henc e, the use of capture net anomalies of hydropsychid larvae could represent a valuable indicator of sublethal toxicity induced by malathion and other o rganophosphorus insecticides in running waters. (C) 2000 Elsevier Science B .V. All rights reserved.