Insect Damage 49 



especiallv of coniferous trees, and feed on the soft cambium 

 layer, are usually secondary troubles, after the vigor of the 

 tree has been undermined by defoliation, by fire, or by other 

 causes. They rarely attack vigorous and healthy trees; 

 sometimes, however, when a pest is excessively abundant, 

 heahhy trees may be attacked and succumb, especially 

 young specimens. Since the larvae of these beetles destroy 

 the cambium, their damage becomes easily very serious, 

 leading to the death of the tree. And as their presence is 

 not readily detected before the mischief is done they are 

 m.ost difficult to deal with. 



Not less insidious and diflicult to combat are the wood- 

 borers and n'ood-wasps which burrow in the wood, or hollow 

 out the pith of twigs. Although they are mostly less injuri- 

 ous to the tree, being usually few in number and working 

 as they do in dead wood, yet when they attack the smaller 

 branches and young trees they may cause undesirable loss. 

 Even in the bole of older trees they may, if very numerous, 

 undermine the vitality of the tree by reducing the conducting 

 tissue so as to eventually cause the death of the less vigor- 

 ous individuals. Moreo\'er, these boring insects may pro- 

 duce mechanical injuries which furnish an entrance for 

 fungus growth and thereby lead to more serious trouble. 



The roots suffer also from a number of insects. Some of 

 them destroy the youngest root tips mechanically, as is done 

 by the mole-cricket and the larva of the June bug, while wire- 

 worms and other beetle larvae, and a few caterpillars and 

 root-lice living underground, feed on them, and others again 

 burrow in them. The damage is usually of moment only 

 in young trees and is, of course to be found in the loss of 

 feeding apparatus. 



There should perhaps here be added, since the question 

 occasionally arises, a few remarks on "how to kill a tree." 



