THE TEMPORARY ABATEMENT OF NUISANCE SPECIES OF TRICHOPTERA WITH DDD (TDE) LARVICIDE

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Abstract
Nuisance species of riverine insects were temporarily eliminated from the Expo 67 site at Montreal in 1967 by four applications of an emulsifiable formulation of DDD (TDE) to the St. Lawrence River, one in each of the months of May, June, July, and August of 1967. In each treatment sufficient DDD was applied 1.5 miles above the infested rapids to provide a concentration of about 0.4 p.p.m. of DDD in the water, throughout a period of about 15 minutes. Each treatment caused the immediate detachment of about 98% of the Trichoptera larvae (mainly Hydropsychidae), and lesser percentages of other aquatic arthropods. No observable effects on fish were detected. Populations of arthropods, especially amphipods, rapidly restored themselves after each treatment. During August 1967, both amphipods and gastropods were more abundant in treated than in untreated rapids. Residues of DDD were negligible and were expected to be relatively non-persistent. Occasional swarms of Trichoptera of relatively minor proportions, detected at the Expo 67 site by light traps, presumably arrived on steady southerly winds from the untreated Lachine Rapids more than 7 miles upriver. Information about the decomposition of DDD and related chlorinated hydrocarbons in nature is reviewed.