REACTIONS OF THE LARVAE OF THREE RHEOPHILIC SPECIES OF TRICHOPTERA TO SELECTED INSECTICIDES

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Abstract
Procedures are outlined for evaluating in aquaria the effects of insecticides against rheophilic species of Trichoptera larvae (Brachycentrus lateralis (Say), Hydropsyche morosa Hagen, and H. recurvata Banks). In general DDT, DDD, and methoxychlor were considerably more toxic than were malathion, Baytex®, or diazinon and their regression lines were steeper. Some of the methoxychlortreated larvae recovered within 18 hours after treatment but the reverse was true for DDT, DDD, and the organophosphates. DDT dissolved in ethanol was considerably more toxic than any of the three commercial formulations of DDT tested. Sensitivity to DDT declined (i.e.LC50 values were higher) with increasing size (age) of the larvae. LC50 values of DDT also varied directly with the densities of tested populations in tests containing more than 10 larvae per 250 ml of water. Toxicities of all chlorinated hydrocarbons varied indirectly with the temperature and those of the organophosphates directly. The significance of these findings to laboratory and field tests is discussed.