INSECT ENEMIES OF WESTERN FORESTS 7 



pandora moth, was only 48 percent of the normal, amounted to 294,- 

 000 board feet, leaving a net loss for the 11 years of 32.3 percent ol 

 the stand. 



The lodgepole pine forests of Idaho, Montana, and Wyoming, par- 

 ticularly those in and around Yellowstone National Park, have suf- 

 fered tremendous losses in recent years. It has been conservatively 

 estimated that during the 10 years that ended with 1932 these losses 

 amounted to 7,250,000,000 board feet, more than 36,000,000 trees hav- 

 ing been killed in one national forest alone. Many mature lodgepole 

 pine forests in regions 1, 4, and 6 have been completely destroyed 

 during the last 20 years, or are in process of destruction, by the 

 mountain pine beetle. 



During the 10-year period 1923-32 the mountain pine beetle is also 

 estimated to have destroyed 110,000,000 board feet of valuable stands 

 of western white pine in northern Idaho. 



It must be clearly understood that these loss estimates cover the 

 normal as well as the unusual drain on the forest. In the surveys in 

 the ponderosa pine type of California and Oregon, for example, all 

 trees killed by bark beetles w^ere tabulated. Normally, on the best 

 sites but few trees (30 to 40 M board feet per section) are thus killed 

 each year, but on poorer sites losses of 50 to 100 M board feet per 

 section may not be unusual. In lodgepole pine stands normal losses 

 by bark beetles are practically negligible, so any marked losses indi- 

 cate abnormal conditions. 



Defoliating insects at times destroy considerable stands of mature 

 timber. These outbreaks, however, usually occur at rather long in- 

 tervals and are nearly always of short duration. In western forests 

 some of the worst defoliators are the pine butterfly, the Douglas fir 

 tussock moth, the spruce budworm, and the hemlock looj)er. In 

 1893-95 the pine butterfly practically wiped out the mature ponderosa 

 pine stand on 140,000 acres of the Yakima Indian Reservation in 

 Washington. Since then less severe outbreaks of this insect have oc- 

 curred from time to time. In the 3 years 1930-32 the Douglas fir 

 tussock moth destroyed a high percentage of the Douglas fir stands 

 on 300,000 acres of the Colville National Forest in northeastern 

 Washington. Along the coast of Oregon and Washington the hem- 

 lock looper appears at intervals of about 10 years and completely 

 destroys the western hemlock and associated trees over large areas. 

 In Pacific County, Wash., between 1930 and 1932 this insect killed, 

 approximately 200,000,000 board feet of w^estern hemlock and other 

 species on an area of approximately 32,000 acres. An outbreak 

 in 1919-21 covered 500,000 acres in Tillamook and Clatsop Counties, 

 Oreg. Defoliators in general cause either little loss or widespread 

 destruction. 



Forest plantations are particularly subject to the destructive ac- 

 tivities of insects, chiefly because a plantation is usually made up of 

 a large planting of a single species. Then, again, many plantations 

 are established on soils that are not especially suitable for the tree 

 species used ; in such cases soil-infesting insects, such as white grubs, 

 wireworms, root maggots, and cutworms, play an important part by 

 feeding on the roots. Young trees and second-growth stands are 

 often seriously damaged also by insects that feed on the terminals. 



