destructive to some trees in the same grove than it is to others. It is 

 more destructive, also, to young saplings and the branches of medium- 

 sized trees than to the larger trees. 



The death of a tree is caused principally by injuries to the inner bark 

 and cambium resulting from repeated attacks. Injuries to the wood 

 alone do not result in the death of trees, except when all of the wood is 

 practically destroyed or sufficiently injured to cause the tree to fall or 

 be broken down by the wind. 



The commercial value of the wood product is diminished or destroj'ed 

 by the worm-hole defects, but for certain purposes, as, for instance, fence 

 posts, a limited number of such defects are not detrimental, except so 

 far as thej^ may contribute to decay. 



EVIDENCES OF ATTACK. 



The first evidence of attack is fine brownish boring dust and wet spots 

 on the bark, first observed in April, when the overwintered larvse begin 

 to enter the inner bark. As soon as the larvie 

 begin to groove the surface of the wood and 

 enter the sapwood, their presence, in addition 

 to the wet spots, is indicated by yellowish bor- 

 ing dust mixed with liquids and the gum-like 

 exudations. After all of the larvae have entered 

 the wood their presence is plainly indicated by 

 the quantities of yellowish boring dust lodged 

 in the loose bark on the trunk, in the forks of 

 the tree or branches, and around the base. At 

 this stage, usually about the middle of May, 

 the badly infested trees which will die are 

 plainly indicated by the failure of the leaf buds 

 to open or bj^ the dwarfed or faded and sickly 

 appearance of the foliage and, toward the last 



of the month until the larvae have completed their work in .Jal3% by 

 the breaking down of the branches and small trees. 



mm mmm 



Fig. 2.— The locust borer 

 iCullene ro bini ce) : a, 

 eggs; b, c, larvte from 

 hibernation cells. Much 

 enlarged (author's illus- 

 tration). 



FAVORABLE AND UNFAVORABLE CONDITIONS FOR DESTRUCTIVE WORK. 



Favorable conditions for the destructive work of the borer appear to 

 consist in the presence of isolated trees and groves in the open, in local- 

 ities where golden-rod is present or abundant and where less resistant 

 varieties of the tree prevail. 



Unfavorable conditions are found in forest growth or large areas of 

 pure stands, or mixed stands where the locust predominates ; also in 

 plantations and groves where resistant varieties prevail and where there 

 is no golden-rod or other favorite food for the beetles. It is also found 

 that coarse, thick bark is less favorable than the thinner bark on old 

 and young trees and saplings. 



