FOREST PROTECTION 



213 



Table 132. — Expenditures jor direct control of 

 forest insects, continental United States, 1952 



Insect and section 



State and 

 private 



Federal 



Total 



Pine beetle: 



South 



West 



Engelmann spruce 

 beetle: 



West 



Spruce budworm: 



West 



Gypsy moth: 



North 



Other Defoliators: 



North 



South 



Dollars 

 51, 900 

 37, 700 



5,000 

 147, 000 



972, 000 



1,900 



13, 000 



800 



Dollars 

 97, 700 

 136, 600 



691, 100 

 594, 600 

 800, 000 



2, 150 



3, 100 



4, 200 



9,550 

 5,500 

 3, 700 



Dollars 

 149, 600 

 174, 300 



696, 100 



741, 600 



1, 772, 000 



4,050 

 16, 100 



West 



Miscellaneous: 

 North 



5, 000 

 9, 550 



South 



West 



18, 000 



23, 500 

 3, 700 









Total 



1, 247, 300 



2, 348, 200 



3, 595, 500 



Biological Control — A New Tool Against 

 Forest Insects 



Efforts have been made to hasten forest insect 

 control through artificial propagation of their 

 natural enemies. In the case of introduced pests, 

 such as the gypsy moth, conspicuous success has 

 followed the introduction of its natural parasites. 

 Recently, effective control of the European pine 

 sawfly has been obtained by gi'ound and aerial 

 spraying with an insect virus disease. 



Insect Control Through Silvicultural 

 Modifications 



Another promising method of controlling native 

 forest insects is thi'ough silvicultural techniques 

 or forest-management practices. By modifying 

 the stand so as to make conditions less suitable 

 for insect attack, some insect damage can be 

 prevented. 



Studies of the spruce budworm in balsam fir 

 stands have indicated that losses are most serious 

 in mature and overmatm'e stands, and where a 

 high percentage of balsam fir occurs. This suggests 

 that losses might be reduced by operating balsam 

 fii" stands on a shorter cutting cycle and by reduc- 

 ing the percentage of balsam in mixed stands. 

 Attacks by the white pine weevil appear to be less 

 serious where the white pine is grown in dense 

 stands for the fii'st 20 years or so, or in mixture 

 with hardwoods, particularly where the pines are 

 partially suppressed by the hardwoods. 



Some bark beetle outbreaks have developed in 

 the host material provided by fires, windfalls, 

 slashings, and drought. To the extent that these 



conditions can be controlled, or the weakened 

 and killed timber promptly salvaged, beetle losses 

 can be diminished. 



Among the bark beetles, control through forest 

 management has been developed satisfactorily for 

 the western pine beetle and the JeftVey pine beetle 

 in the interior ponderosa pine type. It has been 

 amply demonstrated that cutting and removing 

 trees with the highest beetle risk, usually from 15 

 to 25 percent of the stand, will effectively control 

 these beetles for periods up to 15 years, even though 

 neighboring stands remain infested. This method 

 of prevention or indirect control has entirely sup- 

 planted direct methods of controlling these beetles 

 on commercial forest lands where logging is 

 feasible. 



There is much need for research to develop 

 forest-management practices that will reduce or 

 control damage by insects. So far, only the first 

 steps into this broad field of control through 

 modified silviculture have been taken. There will 

 still be a need for direct or biological measures of 

 control for those destructive forest insect species 

 that do not depend upon adverse forest conditions 

 for the success of their outbreaks. Recent trends 

 have been away from sole reliance on direct 

 control methods, and toward giving greater em- 

 phasis to biological and silvicultural control 

 techniques. 



So much remains unknown concerning the habits 

 of forest insects, the factors governing outbreaks 

 and their duration, and methods of control that 

 progress in insect control through silviculture is 

 closely related to research progress in forest ento- 

 mology in general. 



Opportunities for Salvaging Insect- 

 Killed Timber Improving 



The 5 billion board-feet of timber killed by 

 insects in 1952 is made up of two components: 

 First, the yearly endemic loss that is more or less 

 evenly distributed throughout the entire forest 

 area. This comprises probably two-thirds of the 

 total, or 3.3 billion board-feet. Second, the 

 epidemic losses, which are more or less concen- 

 trated, comprise the remaining one-third, or about 

 1 .7 billion board-feet. Much of the latter, at least, 

 could be salvaged for commercial use. 



Large volumes of insect-killed timber have re- 

 cently existed in certain areas. These include 5 

 billion board-feet of spruce devastated by the 

 Engelmann spruce beetle in western Colorado, 12 

 billion board-feet of Douglas-fir in Oregon and 

 Washington killed by wind and bark beetles, and 

 another 3.7 billion of recently killed Douglas-fir 

 in the Northern Rocky Mountain Region. A high 

 percentage of the present mill capacity in these 

 areas is operating on insect-killed timber, but 

 is able to utilize only a small part of the total. 



