Experimental studies on macroinvertebrate predator–prey impact of pesticides. The reactions of Rhyacophila and Hydropsyche (Trichoptera) larvae to Simulium larvicides

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Abstract
Acute toxicity tests with the predaceous trichopteran larvae of R. dorsalis and H. pellucidula in a laboratory-stimulated stream have shown that both species have a high survival rate after short exposures, 15 min-1 h, to concentrations of temephos(Abate) and chlorpyrifos methyl that produce a mortality of 90% or more in late-instar Simulium larvae. A similar differential reaction to the synthetic pyrethroid permethrin was demonstrated in the case of Hydropsyche but not Rhyacophila. The implication of these findings is discussed in relation to the environmental impact of Simulium control programs based on application of larvicides to rivers and streams and to the problem of evaluating the impact of pesticides and allied toxic chemicals on stream ecosystems. Although significant differences in tolerance level to some insecticides between prey (Simulium) and predator (trichopteran larvae) can be demonstrated in the laboratory, the margin of safety is not sufficiently wide to assure selective control of Simulium larvae by these chemicals under the less precise conditions of larvicide application in the field.