The Effects on Fish, Birds and Mammals of DDT Used in the Control of Forest Insects in Idaho and Wyoming

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Abstract
In connection with projects for forest insect control in Idaho and Wyoming, the effects of DDT on the fish, birds and mammals were studied by direct field observations and by censuses to determine population trends. In Idaho some cottoids, mountain suckers and black bullheads were killed by DDT, but speckled dace, redside shiners and 3 spp. of trout were apparently unharmed. Birds and mammals apparently were not adversely affected by the application of 1 lb. per acre. In Wyoming several cutthroat trout were killed by DDT applied at the rate of 2.5 lbs./acre. These represented only a small % of the total population. A few birds were killed with exptl. application rates of 2.5-7.5 lbs./acre. Mammals were unaffected, with the possible exception of a few chipmunks and a shrew which showed symptoms possibly resulting from DDT. In both states, great amounts of invertebrate food organisms were killed. This apparently had no immediate effect on the terrestrial vertebrates, but in aquatic situations a conspicuous removal of food items caused changes in the diet of the fishes. Susceptibility to DDT poisoning appears to be greater in the lower vertebrates and less in the higher vertebrates. There is marked specific and individual variation in susceptibility to the poison.

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