EFFECTS OF DDT AND OTHER INSECTICIDES 



SUMMARY 



17 



Investigations during 1947 of 

 insecticide-wildlife relationships 

 included field and laboratory tests, 

 and evaluations of actual opera- 

 tions. 



In one area of more than 400,- 

 000 acres of forest land in Idaho, 

 DDT in oil was applied by airplane 

 at the rate of 1 pound to an acre 

 for control of the Douglas fir tus- 

 sock moth. Studies near the 

 center of a large, continuously 

 treated block indicated about the 

 same wildlife eff'ects as had pre- 

 viously been found in smaller 

 units. Birds and mammals were 

 unaffected. Fishes were affected 

 but slightly in the area as a whole, 

 but rather heavy losses of some 

 species were noted in limited re- 

 gions. Uneven spray distribution 

 or unintentional retreatment may 

 have been the cause for the heavy 

 fish kill in some parts of the area. 



In two forest areas in Wyoming 

 aerial applications were made of 

 DDT in quantities of 5 to 10 

 pounds to an acre and of the 

 gamma isomer of benzene hexa- 

 chloride in quantities of 1 and 2 

 pounds to an acre. In the tests on 

 the Teton National Forest, treat- 

 ments of 5 and 7i^ pounds to an 

 acre caused heavy bird damage, 

 and there were indications that 

 mammals were also affected by the 

 heavier application. The destruc- 

 tion of fishes was not so heavy as 

 has been found elsewhere with 

 much lighter dosages. A continu- 

 ous chain of beaver dams, which 

 retarded the flow of the stream 



and reduced the mixing of the 

 DDT-oil solution with the muddy, 

 debris-filled water, probably mini- 

 mized the effects of the spray. 



None of the experimental appli- 

 cations of DDT and benzene hexa- 

 chloride in tests in the Black Hills 

 produced measurable effects on 

 birds or on five species of live- 

 trapped mammals. The small size 

 of the plots and the fact that the 

 birds were through nesting and so 

 not restricted to territories prob- 

 ably lessened the possibilities of 

 poisoning. 



Evidence that the size of the 

 treated area and the time of spray- 

 ing with reference to seasonal bird 

 activity may strongly modify 

 spraying effects was also found in 

 studies made near Albany, Ga., 

 where DDT at the rate of 2 to 6.5 

 pounds to an acre was applied to 

 an area in pecan weevil control 

 operations. 



Indications of a heavy song-bird 

 mortality were found in prelimi- 

 nary studies in a Maryland apple- 

 orchard district where seasonal 

 totals of more than 50 pounds of 

 DDT to an acre had been used. 



In an experimental progranl of 

 tick control in Texas in which 

 DDT dust in the quantity of 4.36 

 pounds to an acre was used, there 

 was a 50-percent reduction in the 

 bird population. Mammals were 

 slightly affected, if at all, and some 

 kill of amphibians and reptiles was 

 observed. 



In a Maryland woodland the ex- 

 perimental aerial treatment of 



