380 WEST VIRGINIA EXPERIMEN1 STATION. 



country infest this class of trees. Every part of a pine tree may 

 be attacked by one or more species from the roots to the 

 terminal twigs, and even the cones. A large number enter and 

 breed in the bark alone; while others may occupy both the 

 bark and wood, and a number of species enter and breed in the 

 wood alone. 



GROUPED ACCORDING TO HABIT. 



Species which breed in the bark of the roots, trunk and 

 branches, are called bark beetles. Those which enter the wood 

 direct are called timber beetles or ambrosia beetles, while 

 those which infest the bark or wood of the twigs, are called 

 twig beetles. 



Some of the species of the family prefer to enter the bark or 

 wood of living trees, in fact there are a tew which will attack 

 none but living trees. There are others which are capable of 

 attacking and mining in the living bark and wood, but prefer 

 to infest that of recently felled, injured and dying trees; the 

 partly living bark of which, offers the most favorable condition 

 for the development of their broods. This class ofScolytids, 

 which are by far the most numerous, will not attack healthy 

 living trees if unhealthy or felled ones are to be found. 



There is still another class represented by numerous species 

 which never attack living trees, but infest the bark and wood 

 after it is dead, and in some cases after it is dry and seasoned. 



The class of Scolytids which attack healthy living trees and 

 cause their death by mining under the bark; and those which 

 render the partly living or sound wood worthless by their gal- 

 leries and attending stained streaks or rapid decay, are termed 

 destructive scolytids. Those which attack only diseased, in- 

 jured, or felled trees, or merely hasten the death of those at- 

 tacked by other species, are termed allies of the destructive 

 species or simply injurious scolytids. While those which in- 

 fest only the dead bark, wood, or twigs, ma} 7 be referred to as 

 neutral scolytids, since they are neither destructive nor injur- 

 ious to a commercial product. They may also be grouped ac- 

 cording to the character of their attack as those making the 



