316 THE PRINCIPLES OF HANDLING WOODLANDS 



In attacking an insect invasion the attempt is not 

 made to destroy all the insects. That would be im- 

 practicable, and fortunately it is not necessary. A destruc- 

 tion of a part of the insects checks their further multi- 

 plication, scatters the energy of the invasion, and subjects 

 the remainder to check by their natural enemies. Often- 

 times it is necessary to destroy only SO to 75 per cent of 

 the broods. 



The most serious problem of insect control is in the 

 great coniferous forests of the South and the West, where 

 there is almost constantly a certain amount of damage by 

 some species of bark beetle. As soon as there is danger 

 of an invasion immediate steps should be taken to de- 

 stroy enough of the insects to check their further multi- 

 plication. If there is a market for the timber, the trees 

 containing the broods may be cut and removed with lit- 

 tle or no extra expense. Frequently, however, the dep- 

 redations occur in the remote forests, where there is no 

 market for the timber, or only the largest and best trees 

 can be sold. Under such circumstances the work of 

 control must be largely an investment representing in- 

 surance, just as in the case of expending money to fight 

 dangerous forest fires. 



One method of destroying insects is to cut the trees 

 down and destroy the bark on the main trunk. Another 

 method is to peel the bark from the body of standing 

 trees to a height of about 20 to 30 feet. If the work is 

 done at the right season of the year it is necessary only 

 to remove the bark, without burning it. This method 



