CIRCULAR 15, FISH AND WILDLIFE SERVICE 



plied, many factors are involved 

 in determining its ultimate effects 

 on fishes and wildlife. 



The type of formulation, size of 

 the area, and the method, fre- 

 quency, and time (season) of ap- 

 plication are some of the highly 

 important variables. Many com- 

 binations of these are to be found 

 in the numerous methods of con- 

 trol, and for this reason it is diffi- 

 cult to make specific recommenda- 

 tions that will apply to the use of 

 DDT generally. 



Because of the intricate rela- 

 tionships existing between many 

 forms of wildlife and their inver- 

 tebrate food species, there are defi- 

 nite limitations to what can be 

 accomplished in the laboratory by 

 way of evaluating effects of con- 

 trol agents on wildlife. The fact 

 that a product is of high toxicity 

 to vertebrates in the laboratory 

 may not in itself be a valid basis 

 for judging its full effects under 

 conditions of field use. The sum- 

 mary removal of a basic food sup- 

 ply by a control operation may 

 prove critical to fishes and wildlife 

 even though the direct kill by poi- 

 soning is nominal. Consequently, 

 in the continuing studies of eco- 

 nomic poisons and wildlife, em- 

 phasis is being placed on evalua- 

 tions under conditions of actual 

 use. 



During 1947 studies were con- 

 ducted in several western forest 

 areas during which DDT in quan- 

 tities of 1 to 10 pounds to an acre 

 and the gamma isomer of benzene 

 hexachloride in quantities of 1 

 and 2 pounds to an acre were ap- 

 plied by airplane. The size of 

 treated areas varied from small 

 experimental plots of 25 acres to 

 one that included more than 400,- 

 000 acres. An experimental aerial 

 treatment of a forest area near 

 Beltsville, Md., was made, using a 

 dosage of 5 pounds of DDT to an 

 acre; and a 1-mile section of a 

 West Virginia bass stream was 

 treated experimentally with a 

 dosage of 1 pound of DDT to an 

 acre. 



Other studies in 1947 included 

 follow-ups of the effect of apple- 

 orchard spraying in Maryland and 

 pecan-weevil control in Georgia. 

 Detailed studies were made of the 

 effects on wildlife of an experi- 

 mental attempt at tick control in 

 Texas. Laboratory tests also were 

 made at Leetown, W. Va., to de- 

 termine the acute toxic levels for 

 fishes of several new insecticides ; 

 and at the Patuxent Research Ref- 

 uge, Laurel, Md., the chronic poi- 

 soning effects of several new ma- 

 terials on quail were measured. 

 At Milford, Conn., DDT, as it is 

 used in certain insect-control prac- 

 tices, was evaluated for its possi- 

 ble effects on oyster management. 



