24 



various species of bark-beetles and wood-borers; and the normal loss from this 

 cause is so very great, when large areas are considered, that it should receive 

 serious consideration. When coniferous trees die without any apparent external 

 injury, examination usually shows that their death has been hastened or caused 

 by bark-beetles or other insects. When slashings are allowed to lie, the fresh 

 bark and wood serves as a breeding ground for many destructive insects, and it 

 is therefore only to be expected that the annual crop of scattered dying trees 

 will be abnormally large in the neighbourhood of bodies of neglected recent 

 slash. It unfortunately happens that nearly all these scattered dying trees are 

 completely destroyed by boring beetles during the few years following their 

 death, and they become an absolute loss; since, even though the limit is being 

 logged, it is often considered unprofitable to collect the scattered dying trees. 

 Properly conducted slash burning will almost invariably reduce the amount of 

 this annual loss, and it must be regarded as a most valuable method of insect 

 control. 



SPORADIC OUTBREAKS. 



From time to time small local bark-beetle outbreaks occur usually in the 

 neighbourhood of slash from cuttings, wind falls, or fire-killed timber. The 

 beetles concerned are frequently common secondary species, which, having had 

 suitable opportunities for rapid breeding, find themselves numerous enough 

 to attack the nearby green timber successfully ; these have already been referred 

 to under " Secondary Enemies," page 23. These minor outbreaks are easily 

 controlled, and may die away without causing extensive injury; on the other 

 hand, if they have been originated by some of the more destructive species, 

 they may become epidemic, and devastate the whole countryside. Small 

 outbreaks by a destructive primary enemy should not be disregarded. 



EPIDEMIC OUTBREAKS. 



Bark-beetle outbreaks may be considered epidemic when they spread 

 rapidly over a wide area, involving the death of many hundreds or thousands 

 of trees. Under these conditions the beetles occur in immense numbers, and 

 attack the green timber with the greatest readiness. Often the largest and 

 finest trees are selected. The one or more primary enemies really responsible 

 for the spread of the injury are accompanied invariably by numbers of secondary 

 species. Many examples of these extensive injuries have occurred in Canada 

 and the United States during the last century. The Destructive Eastern Spruce 

 Bark-beetle, Dendroctonus piceaperda Hopk., has killed many millions of feet of 

 spruce timber in Maine and New Brunswick during a series of destructive 

 outbreaks, the last of which occurred between the years 1897 and 1900. The 

 best known Canadian examples are those still spreading in the yellow pine in 

 southern British Columbia, caused by the Western Pine Bark-beetle and the 

 Western White Pine Bark-beetle, and those in the western white pine and 



PLATE 6. 



BARK-BEETLE BREEDING GROUNDS (ORIGINAL). 



Fig. 1, A slashing on Vancouver Island; an ideal breeding ground for beetles. 



Fig. 2, Beetle-killed yellow pine, Indian Meadows, B.C. 



Fig. 3, Beetle-killed western white pine, B X Mountain, B.C.; the dead trees were killed by the 



Western White Pine Beetle many years ago. 

 Fig. 4, Beetle-killed lodgepole pine, Trepanier Creek, B.C. 



