322 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



Printinp:, A./iere (loverimient bond paper and postao;e stamps were 

 destroyed; dania<!:e to the woodwork of one of the new buiklings at 

 the Sohli^n-s' llonie; continued (hunaoje to the floors of the old Na- 

 tional Musoum buildini; and to stored material; dama<j^e to the <rreen- 

 liouses and i)hints of the \Var Depai-tmeiit and to the dwelling; of 

 the Secretary of War. ^Serious damage to fruit trees and vegetable 

 crops by these insects was reported from California. 



Hie damage to crude forest ])roducts by wood-boring insects con- 

 tinues to cause extensive losses througliout the forested sections of 

 the country where logging operations are ( arried on. 



Principal lines of investigation and results. — The principal 

 lines of investigation carried on during the year have included the 

 continuation of an intensive study of the character and extent of the 

 damage caused by tree-killing barkbeetles and methods of con- 

 trolling them in some of the principal national and private forests of 

 the Pacific slope and Rocky Mountain regions. 



In southern Oregon a study was made of the causes of the natural 

 increase and decrease of the Avestern pine beetle, including records 

 on 2,549 trees, representing a volume of over 2,000,000 board feet. It 

 was found tliat the average killed tree was attacked by 2,070 beetles, 

 which deposited over 74,000 eggs in the bark, but that only about 30 

 per cent of these developed to the beetle stage. It was also found 

 that out of the number of beetles that develop in and emerge from 

 the trees killed by them, only about 3 per cent survive to continue 

 the attack on other trees. This furnishes important evidence as to 

 why the percentage principle of control is successful, for this 3 per 

 cent survival is still further reduced in attacks that fail and by 

 natural enemies and other natural causes until there is a much 

 smaller percentage to congregate in sufficient force to continue the 

 killing of trees. Thus in artificial control, I)}' which a sufficient 

 percentage of the killed trees are treated to reduce the numbers of the 

 beetles below their power of concentration in sufficient force to over- 

 come the natural resistance of the living trees, the beetles cease to be 

 a menace and the problem is solved. 



Inspections during May. 1920, of the area in the Middle Fork basin 

 of the Sequoia National Park, where control work was conducted 

 by the National Park Service, the Forest Service, and the Bureau of 

 Entomology, showed that, while 1,055,000 board feet of yellow pine 

 and sugar pine timber had been killed by beetles in 1917, the treat- 

 ment of 52 per cent of the volume of the infestation in 1918 was 

 followed by a decline of 71 per cent in the total loss of the preceding 

 year. In the 3'ellow pine alone 60 per cent of the infestation was 

 treated and the subsequent decline amounted to 81 per cent. 



Experimental trap tree work was carried on during the summers 

 of 1919 and 1920 in the Marble Fork and Cactus Creek Basins of 

 the Sequoia National Park at a cost of $500. As a result both basins 

 are now free from evidence of any serious infestation. 



A detailed study of the character and extent of depredations by 

 tree-killing beetles in the pine forests of California, as represented 

 by Federal Forest District 5, shows that during one year, 1917, ap- 

 proximately 90,000,000 board feet of yelloAv pine and sugar pine 

 were killed by the western pine beetle and mountain pine beetle. 



