We are concerned only with the following three classes of 

 insects : 



1. Primary insects 



2. Secondary " 



3. Beneficial " 



Primary insects are the species direct^ respon- 

 sible for the death of the tree. Secondary insects are thnr-:; 

 injurious species associated with the primary, which seldom 

 kill trees b\it often parts of trees, limbs, etc. Beneficial 

 insects belong to the group prejring on the other two. Most 

 species of trees have but one or two primar;?" species of in- 

 sects. A primary species may be confined to one species of 

 tree or may be primary on several tree species. 



Again, a secondary insect in mature trees may be 

 a primary insect in immature trees, or poles and saplings. 

 This is caused by the habits of individual species. In this 

 relation they may be divided under each species of tree. 

 Thus we ms.y divide prima^r insects into two groups: 



1. Attacking parts of trees with cork-scaled 



bark. 



2. Attacking trees or parts of trees with- 



out cork-scaled bark. 



Under the first group would come the bark -boring 

 beetles of the genus Pendroctonus, several flathead borers 

 of the family Buprestidae, and in the case of firs a round- 

 head or longhorn Beetle belonging to the family Cerambycidc.e 

 These beetles may attack the second group if trees but as a 



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