Insect Damage 4^ 



on the soft cambium layer underneath the bark; the stem- 

 borers hollow out twigs or make their abode in the trunks, 

 feeding on the wood itself. 



Some do little or practically no damage; indeed, in the 

 majority of cases only when an extraordinary development 

 of an insect pest in any one season takes place, or when 

 repeated invasions have to be endured, or when other acces- 

 sory unfavorable conditions occur, need any apprehension 

 for the hfe of the tree be felt. Such unusual developments 

 of insect pests seem to take place periodically, when, due to 

 specially favorable seasons or otherwise, the pest is favored, 

 while natural enemies are reduced or less favored. 



The leaf-eaters of certain species are especially Hable to 

 this periodic excessive multiplication. 



If the defoliation is only partial and occurs at a time of 

 the year vhen the foliage can still be replaced by the 

 development of the dormant buds, outside of the temporary 

 unsightHness, only a reduction in the season's growth is the 

 result. But, if ti^e defoliation is complete, and, as happens 

 with some species ^jf leaf eaters, more than one generation 

 is developed in snason, repeating the destruction of the 

 foliage as new Iraves are formed and thereby preventing 

 the assimilation of food materials, the tree may be weakened 

 even to death. At least a repetition of the defoliation for 

 two or possibly three seasons, according to the vigor and age 

 of the tree, will be fatal. 



The new foliage, formed in the same season after the first 

 defoliation, is apt to be smaller in size or abnormal in form 

 and thinner, hence less effective. Sometimes, however, 

 when a large number of buds have been destroyed, unusu- 

 ally large and abnormally formed secondary leaves arise 

 from the few remaining buds. In either case the nutrition 

 of the tree is interfered with. 



