II. 



BARK-BEETLE INJURIES AND THE MEANS OF CONTROL. 



Bark-beetle Injuries. 



The majority of our bark-beetle species breed commonly in dying trees 

 and slash, but many of these attack trees which have become weakened or 

 unthrifty, or even at times healthy trees, and they are therefore distinctly 

 injurious. Other species attack healthy trees readily when the beetles are 

 present in sufficiently large numbers, and have killed an enormous quantity of 

 timber in Canadian forests. 



The injury to living trees is caused by the adult beetles cutting their egg- 

 tunnels through the inner bark or upon the surface of the sap wood, and by the 

 larvae excavating the larval-mines in the same location. 



The multitude of tunnels and mines checks the flow of sap and rapidly kills 

 the tree, or the part of it attacked. Direct injury to the timber is caused by 

 the Ambrosia-beetles, since their small black tunnels penetrate the wood for 

 several inches or, in some cases, for more than a foot. 



PRIMARY enemies. 



Certain of our bark-beetle species are commonly found attacking and 

 killing heal hy timber. They attack perfectly sound trees and cause the chief 

 or primary injury, and they are therefore known as " primary " enemies. 

 Among our best known examples are: Dendroctonus brevicomis Lee, D. monticolce 

 Hopk., D. piceaperda Hopk., D. horealis Hopk., and Dryoccetes confusus Sw. 

 These are also found breeding in slash, and in timber dying from various causes, 

 but they are commonly and abundantly found attacking healthy timber in 

 quantity. 



A considerable number of our species breed everywhere in slash and dying 

 trees and are usually secondary enemies, but upon occasion, the frequency 

 varying with the species and the conditions for rapid breeding, they increase to 

 immense numbers so that they successfully attack healthy trees and become 

 important primary enemies. Polygraphus rufipennis Ky., the Four-eyed Spruce 

 Bark-beetle, is abundant throughout Canadian forests in spruce bark of slash 

 and dying trees; but it attacks and kills large numbers of over-mature trees, 

 and those weakened by other causes, and at times becomes epidemic, killing 

 large quantities of spruce, particularly black spruce. Pityokteines sparsus Lee, 

 (Ips halsanieus Lee), the Balsam Fir Bark-beetle, is an important primary 

 enemy of the balsam fir in Eastern Canada. It is an important factor in the 

 present extensive injury to our eastern balsam, and is always active in killing 

 the over-mature and weakened trees. It is everywhere abundant in dying fir 

 bark. Dendroctonus pseudotsugae Hopk., the Douglas Fir Bark-beetle, is every- 

 where abundant in slashings of Douglas fir and western larch, but is at times 

 an important primary enemy in restricted localities. D. ohesus Mannh., the 

 Sitka Spruce Bark-beetle, is rather more commonly found as an important 

 primary enemy of Sitka spruce on the British Columbia coast, but it usually 

 confines itself to dying bark if this is available. Several of our species of Ips, 

 and many other species, while usually important secondary enemies, are at 

 times of considerable primary importance in sporadic outbreaks. All these 

 primary enemies, in order to overcome the resistance of the healthy trees, must 

 attack in very large numbers, so that their numerous and rapidly excavated 

 tunnels may check the sap flow in a short time. In an epidemic outbreak of 



