EFFECTS OF DDT AND OTHER INSECTICIDES 



FOREST INSECT CONTROL 



MOSCOW. IDAHO 



In May and June 1947 about 

 400,000 acres of forest land near 

 Moscow in northern Idaho were 

 treated for control of the Douglas 

 fir tussock moth. DDT in oil, in a 

 dosage of 1 pound of the toxicant 

 to an acre, was applied by airplane. 

 Follow-up studies were made of 

 the eflTects on fishes, birds, and 

 mammals. 



This project offered an unusual 

 opportunity for evaluating on a 

 large operational scale some of the 

 findings on relationships between 

 wildlife and insecticides that have 

 been obtained on much smaller 

 experimental plots. Unfortunate- 

 ly, however, the control phases of 

 the project were divorced from the 

 investigational work, so planned 

 studies could not be made. The 

 spraying schedule, for instance, 

 was highly flexible, and spray 

 dates for specific areas could not 

 be determined in advance. With- 

 out this information it was im- 

 possible to time "before" and 

 "after" studies to the best advan- 

 tage. 



Mammals 



An attempt was made through 

 live-trapping in two plots to deter- 

 mine the possible effects of the 

 spraying on small mammals. A 

 40-acre study unit area was locat- 

 ed near the center of a treated 

 area of 50 square miles. Live- 

 traps were placed grid fashion at 

 4-chain intervals. A second study 

 unit, 11/2 acres in size, was near 



the edge of a large treated block. 

 Traps in this case were set at 2- 

 chain intervals. In both units 76 

 traps were operated for 428 trap- 

 nights, and 67 individual mam- 

 mals were taken a total of 147 

 times. The species taken by live- 

 trapping included the red-backed 

 mouse, white-footed mouse, jump- 

 ing mouse, and two species of 

 chipmunks. These limited sam- 

 ples of the population revealed no 

 marked effects of the spraying. 

 Aside from the mammals taken in 

 trapping, others were under ob- 

 servation. In all, 16 species or sub- 

 species were seen before, during, 

 and after the period of spraying. 



Birds 



Populations of birds were stud- 

 ied intensively on two 20-acre 

 plots, one located within a large 

 sprayed block and another in an 

 untreated check area. Censusing 

 of the plots began June 2 and was 

 continued until July 11. Spray 

 was applied to the study area on 

 June 21. Six censuses were taken 

 in the treated area before, and five 

 after, the treatment. The check 

 plot was censused five times be- 

 fore, and five times after, the 

 study area was sprayed. 



The spraying had no apparent 

 effect on the populations of 44 

 species of birds in the area con- 

 cerned. Prior to spraying, the 

 treated area had a density of 435.5 

 pairs of birds per 100 acres. An 

 average of counts taken after 

 spraying showed a density of 



