INSECT ENEMIES OF WESTERN FORESTS 



225 



Figure 104. — Refilling an insecticide tank on a Stearman plane. 



The largest airplane spraying project ever conducted in the 

 United States up to 1947 was undertaken in northern Idaho, small 

 areas in northeastern Oregon, and eastern Washington, to control 

 an outbreak of the Douglas-fir tussock moth. From May 22 to 

 July 2, 1947, 11 planes made 2,120 runs and deposited 390,878 

 gallons of DDT spray on 413,469 acres of forest land (fig. 105). 

 The spray contained 1 pound of DDT in a solvent with light fuel 

 oil to make 1 gallon of spray for each acre treated. The spraying 

 was phenomenally successful in killing all tussock moth cater- 

 pillars on the treated area. 



The type of aircraft best suited for forest spraying and the 

 equipment needed for carrying and releasing sprays of proper 

 droplet size at the desired rate have been subjects of much 

 investigative and engineering work. Developments have been so 

 rapid and are so specialized that they cannot be adequately 

 covered here. Most of the forest spraying has been done by con- 

 tractors who have special equipment and pilots trained and ex- 

 perienced in this type of work. 



BARK-BEETLE CONTROL 



A tree in which bark beetles have successfully established them- 

 selves cannot be saved, and the best that can be done is to destroy 

 the infesting insects before they are able to emerge and attack 

 other trees (80). Bark-beetle broods can be destroyed by several 

 methods of artificial control (86), the method and time of appli- 

 cation varying for different species and different regions. Though 

 bark-beetle outbreaks can be reduced, these insects cannot be 

 exterminated, so control measures must not be considered as a 

 panacea or cure for all time. The results of a successful bark- 



