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Effects of a C-47 Airplane Application of DDT on Fishfood Organisms in Two Pennsylvania Watersheds
C. H. Hoffmann and A. T. Drooz
The American Midland Naturalist
Vol. 50, No. 1 (Jul., 1953), pp. 172-188
Published by: The University of Notre Dame
Stable URL: http://www.jstor.org/stable/2422162
Page Count: 17
You can always find the topics here!Topics: Streams, Creeks, Trout, Spraying, Aquatic insects, Insect larvae, Food, Fauna, Animal feeding behavior, Food supply
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An area comprising two watersheds totaling 52,000 acres near WilkesBarre, Pa., was sprayed aerially with 1 pound of DDT per acre during May and June 1948 to control the gypsy moth Porthetria dispar (L.). Research was conducted to investigate the effects this application would have on the streambottom insects that serve as food for fish. The sprayed area, check area, treatment, study methods, and distribution of the spray are described briefly. A prespray surface-drift sample contained 11 bottom insects of 3 genera. At the start of spray operations there were 6 insects of 5 genera in a sample, whereas 1/2-hour later the number of affected insects has sextupled. The maximum number of affected insects were caught 21/2 hours after the spraying and consisted of 821 individuals representing many genera. Before and at designated intervals after the spraying the bottom fauna was sampled with a square-foot bottom sampler at 14 stations in the treated area and at 3 check stations. The samples were taken to corroborate drift sample data and to study repopulation. The insecticide rapidly diminished the numbers and volume of bottom insects in the streams, but none of the 14 stations in the treated area were completely depopulated and losses at a few stations were small. Insects of the orders Megaloptera and Odonata appeared to be resistant to DDT poisoning at the dosage applied. Trichoptera were affected severely and were not taken in large numbers and variety until 16 months after the area was sprayed. In general, the trend toward repopulation was evident by August, 2 months after application of the DDT, and by autumn, except for certain caddis flies, the samples revealed ordinary numbers of bottom insects. Certain biological and physical factors hinder the eradication of aquatic insects during large-scale spray operations. These factors include a great variety and abundance of aquatic insects having diverse life histories and habits, variation in susceptibility of species to DDT poisoning, ecological differences in streams, variation in tree canopy, proximity of untreated streams that furnish immigrants for repopulation, and influences of weather on the application and distribution of the insecticide. Chemical analyses of moss, collected from Choke Creek 1 month after the spraying, contained 0, 44, 110, and 128 p.p.m. of DDT at distances of 1, 2, 3, and 6 miles, respectively, from its source. These data indicate that DDT particles accumulate on stream plants in important amounts downstream, coinciding with the insect mortality which increased from the source to the mouth of the stream. It appears that some fish and insect mortality during the first postspray month resulted from this residue.
The American Midland Naturalist © 1953 The University of Notre Dame