i8o FORESTS AND MANKIND 



The bark beetle, for instance, probably the most widely- 

 destructive insect pest the forest has ever known, includes more 

 than four hundred distinct species in America. Some of these 

 beetles attack only one species, others have several victims. 



Their methods are essentially the same. A pair of beetles 

 select a tree through whose bark they dig a tunnel. There the 

 female lays a number of eggs. Time passes. The parents die. 

 The eggs hatch into small white worms that eat tunnels of 

 their own beneath the bark. Later they develop into beetles 

 and work their way out where they swarm to other trees, mate, 

 and repeat the destructive life cycle. The tree's death is brought 

 about by these tunnels which carved by numerous beetles 

 finally girdle the tree and prevent the sap's rising just as effec- 

 tively as if the tree had been cut with an axe. It only requires 

 about ten beetles to the square foot to kill a vigorous tree of 

 average size. 



Hardly a tree exists that is not susceptible to the attack of, 

 at least one species of beetle. Certain trees, such as western 

 yellow pine and western white pine, have suffered great losses 

 from bark beetle alone. Some beetles work in the roots, others 

 in the twigs and others, like the bark beetle, in the soft living 

 wood just beneath the outer bark. 



There is no single remedy for all insect pests and just as 

 the physician studies our bodily enemies, that he may learn 

 the best way of ridding man of their attack, so the lives and 

 habits of these forest insects have been studied in an effort to 

 arrive at the best means of controlling them. It would be im- 

 practical economically and probably impossible actually to 

 exterminate any one of them. Controlling their activities by 

 keeping down their number seems the only possible plan. So 



