INSECT ENEMIES OF WESTERN FORESTS IQl 



Penetrating oils 



Recent experiments in California liave developed some petroleum 

 oils that, when sprayed on the trunk of pine trees, will penetrate 

 the bark and kill the pine beetle broods beneath. The most effective 

 oils developed to date are those of the distillate grade carrying as 

 much naphthalene as can be taken in solution. These when applied 

 to infested ponderosa pine bark at the rate of about 4 ounces per 

 square foot will give mortalities ranging from 50 to 90 percent. Oils 

 of this type, however, are effective only when temperatures are above 

 60° F. and cannot be used at all when the bark is wet. This method 

 of control is still in the experimental stages, with the possibility that 

 it may be useful in treating infested trees during the summer months 

 on recreational areas or late in the spring and early in the fall when 

 the fire hazard is too great to permit burning. 



The peeling method 



The peeling method can be used in the control of those bark beetles 

 that, in the immature stageSj work between the bark and the wood 

 and die of exposure when the bark is removed, and is especially ap- 

 plicable to moderately thick-barked trees that are easily peeled. It 

 has been used extensively in the control of the Black Hills beetle in 

 ponderosa pine of the Rocky Mountain region and in the control of 

 the mountain pine beetle in western white pine. It has the impor- 

 tant advantage of involving no immediate fire risk and is cheaper 

 than the burning method for the treatment of isolated trees less than 

 30 inches in diameter. If the bark tends to adhere to the wood, 

 however, peeling is a very slow, tedious process and in the spring 

 will not destroy overwintering adults, new adults, or pupae in the 

 last stages of development. In general, it is more expensive than the 

 burning method, especially for the treatment of trees in groups. 

 Moreover, it leaves a mass of slash and crisscrossed logs in the woods 

 that seriously increases the fire hazard. 



In carrying out this method, the infested trees are felled across logs 

 or other felled trees to hold them off the ground, and then all of the 

 infested bark is peeled with an ax or barking spud and allowed to 

 drop to the ground where ants, rodents, and exposure dispose of the 

 immature bark beetles (fig. 92). In some rare cases, where all of 

 the infestation is within 20 feet of the ground, the barking has been 

 done with long-handled barking spuds without felling the trees. In 

 such cases, of course, the work can be done more cheaply than where 

 felling the trees becomes necessary. 



Peeling and spreading hark 



A modification of the peeling method, involving the spreading 

 of the bark where it will receive the direct rays of the sun, has been 

 used with a fair degree of success in the control of the western pine 

 beetle and is applicable to the treatment of ponderosa pines infested 

 with broods of this species late in the spring or in the summer in 

 places where burning would be dangerous. 



In this method the tree is felled across a log so as to keep a large 

 part of tiie tru;;ik off the ground, and the bark is peeled and spread 



