INSECT ENEMIES OF WESTERN FORESTS 243 



have cut infested trees and sent them to distant mills or burned 

 the slabs; and this, together with the removal of beetles in 

 recently felled green logs, explains the absence of insect-killed 

 trees around many going logging operations. Of late years this 

 method has come more and more into favor with the opening up 

 of forest tracts and the development of truck logging, which has 

 made possible the removal of scattered infested trees at compar- 

 atively low costs (8 %, 89). 



This method serves the dual purpose of controlling the bark 

 beetles and salvaging timber that otherwise would be completely 

 worthless within a short time. Where the method can be used it 

 is economical and sometimes can be carried out with a small 

 immediate profit from the operation in addition to suppressing 

 the beetle outbreak. Even if the logging operation is carried out 

 at a loss of from $1 to $2 per thousand board feet of timber, it 

 is better than spending $3 or $4 per thousand feet to fell the 

 trees and burn them or leave them in the woods, as is the case 

 with the usual control operations. The reduction of infestation 

 will be the same by either method. 



In inaccessible areas the method cannot be applied except at 

 a cost in excess of that of the ordinary control methods, and of 

 course cannot be used in the control of bark beetles attacking 

 unmerchantable species of trees whose chief value lies in the 

 protection of watersheds or as a forest cover in parks and 

 recreational areas. Moreover, bark beetles introduce blue stains 

 which discolor the sapwood before there is any possibility of 

 salvage, and thus reduce the value of the material. In ponderosa 

 pine areas it rarely pays to salvage tops or trees less than 22 

 inches in diameter, and such unmerchantable material must be 

 burned to complete the control operation. Because of immediate 

 blue staining, the value of the logs taken out of the woods is 

 reduced approximately 50 percent below that of green logs, so 

 returns from the operation must be computed on that basis. If 

 the method is to be effective, the beetles on an entire unit must 

 be destroyed in a single season, which means that the logging 

 operation must frequently be extended over a very large area. 

 This is often difficult, so logging must be supplemented in many 

 cases by the ordinary control methods. 



MAINTENANCE CONTROL 



One season's treatment of an area will rarely be sufficient to 

 bring an outbreak under control. Even with the most careful 

 spotting and treatment some infestation will be missed that will 

 give rise to new infestation the following year. A follow-up 

 program, or maintenance control, is therefore necessary until 

 the normal balance is restored and the bark beetles reduced to 

 an endemic status. 



With infestations of the mountain pine beetle, unless migra- 

 tions occur, a 75-percent reduction is usually obtained following 

 the first season's work, and one or two seasons of maintenance 

 work will usually bring the epidemic under complete control. In 

 western pine beetle control, reductions of more than 50 percent 



