104 MISC. PUBLICATION 273, U.S. DEPT. OF AGRICULTURE 



Figure 44. — A forest defoliated by the spruce budworm. 



In the western part of the United States the true firs and Doug- 

 las-fir appear to be preferred hosts of the spruce budworm, and 

 the greatest damage has occurred in pure stands of these two 

 species. The budworm, or closely related varieties, has also been 

 found attacking Engelmann spruce, western larch, western hem- 

 lock, and western white, ponderosa, and lodgepole pines. Budworm 

 attacks on pines are usually limited to individual trees growing 

 in association with the preferred hosts, though serious outbreaks 

 in pure lodgepole pine have occurred in and adjacent to the south- 

 western corner of Yellowstone National Park. The new foliage is 

 destroyed first, old needles being attacked only when the preferred 

 supply is exhausted. Larvae will often migrate from one tree to 

 another in search of new foliage rather than feed on old needles. 



Like most defoliators, the spruce budworm is preyed upon by 

 numerous insect parasites and predators, and these in normal 

 years tend to keep the pest under control. Natural enemies and a 

 shortage of food will eventually subdue most outbreaks. 



Control of spruce budworm outbreaks by airplane spraying has 

 been demonstrated as feasible by a pilot experiment in 1948 and 

 large scale operations conducted in Oregon and Washington dur- 

 ing 1949, 1950, and 1951 by private timberland owners, State 

 agencies, and the Federal Government. One pound of DDT in 1 

 gallon of fuel oil was applied per acre during a short period in 



