298 



The Black Spruce. 



Small trees are rarely attacked. In the localities visited, 

 from one-half to two-thirds of the spruces with a basal 

 diameter ranging from one to two feet were either dead 

 or dying. Trees of this size are the most suitable for lum- 

 ber and consequently the most valuable. The smallest 

 affected tree noticed had an estimated basal diameter of 

 about ten inches. In this case the attack appeared to be a 

 failure, for so much resin had oozed from the wounds that 

 the work was obstructed. The galleries were scattered and 

 single and their authors were found dead, each in its furrow. 

 No larvse were present and the apparent attempt to establish 

 a colony in this tree had thus far failed. But it may be 

 that this tree had only been attacked for the purpose of 

 obtaining food and had not yet been brought into that 

 sickly, languishing condition thought by some entomologists 

 to be necessary to induce the establishment of a colony, the 

 deposition of eggs and the development of larvae. For it 

 is said of the Scolytus destructor, a bark-mining beetle that 

 sometimes proves very destructive to elm trees in Europe, 

 that the adult insects first attack healthy trees for the pur- 

 pose of obtaining food and when by this means the vigor 

 of the tree has become somewhat impaired the female de- 

 posits her eggs in her galleries. Then the rapidly increas- 

 ing numbers soon destroy the life of the tree. 



When two trees of unequal size stand in clgse proximity 

 the larger one seems to be most liable to be attacked. In one 

 instance two trees stood scarcely more than three feet apart. 

 The larger one had been attacked, the smaller remained 

 unharmed. In another similar instance the larger of the two 

 trees was dead, having been attacked first, the other was dy- 

 ing. Why this preference on the part of these insects for the 

 largest trees ? It may be that young trees are apt to be 

 too resinous to be attacked successfully. In the case of 

 the small tree already mentioned the gummy exudations 

 from the perforations in the bark first attracted my atten- 

 tion. Or the insects may instinctively kuow that a tree 



