314 YEARBOOK OF THE DEPARTMENT OF AGRICULTURE. 

 INJURIES WHICH CAUSE THE DEATH OF TREES. 



The principal insect injuries which result in the death of trees are 

 burrows through and beneath the li\ 7 ing bark of the trunks. There 

 are two distinct classes of these injuries, one caused by bark-boring 

 beetles, the other by bark-boring larvae or grubs. 



INJURIES BY BARK-BEETLES. 



The adults of this class of enemies bore into and beneath the bark 

 for the purpose of excavating galleries in which to deposit their eggs. 

 These galleries are the primary injury which weakens the vitality of 

 the trees, while the secondary or larval mines complete the girdling 

 process which kills them. 



INJURIES BY BARK-BORING GRUBS. 



This class of injuries is caused by larvae which hatch from eggs 

 deposited by the adult insects in the outer bark, and never in burrows 

 beneath it; therefore the burrows made through the living inner bark 

 by the young not only cause the primary injury, but complete the 

 girdling process. 



The form of the barrows or galleries is, as a rule, sufficient to iden- 

 tify at once the class to which a given injury belongs, and very often 

 is sufficient to identify the insect. 



BARK-BEETLE INJURIES TO HICKORY TREES. 



Within recent years the dying of hickory trees has attracted consid- 

 erable attention, especially in the northern tier of States, from Wis- 

 consin to Vermont. The trouble also extends southward through the 

 Atlantic and Eastern States as far as central Georgia and westward to 

 Missouri. Thousands of trees have died, and in some sections nearly 

 all of those in forests, parks, and on farms have perished. This is 

 causing a serious loss not only of a valuable timber product, but of 

 shade trees and the crop of nuts, which latter, in some sections, is of 

 considerable importance, both as a commercial product and for home 

 consumption. This dying of the hickories has been found in every 

 case investigated to be the result of injuries to the buds and twigs and 

 to the bark of the branches and trunks by the hickory bark-beetle 

 (Scolylus Jf-spinosus Say). 



THE HICKORY BARK-BEETLE. 



The hickory bark-beetle is a short, stout, shining black or reddish- 

 brown beetle, averaging 3.6 millimeters (0.14 inch) in length. The 

 wing covers are short and project over the abdomen, which in the 

 males is excavated beneath and armed with four rather prominent 



