23 



the Western White Pine Bark-beetle in western yellow pine more than 2,000 

 pairs of beetles were estimated cutting their egg-tunnels in the trunk of one 

 tree. On the other hand, many examples of abandoned tunnels of various 

 species are found, indicating that the beetles have entered the bark individually 

 or in small numbers, and have been overcome or driven away by the excessive 

 and sustained flow of resin. 



SECONDARY ENEMIES. 



The majority of our bark-beetles are found breeding in bark of dying trees 

 and logs. Many of them readily attack weakened trees or those whi'ch have 

 been injured by fire, primary bark-beetle attack, or other causes, and rapidly 

 effect the death of the trees. They are therefore injurious in the sense that 

 they assist other agencies in killing timber, without themselves attacking healthy 

 trees, and are known as "secondary" enemies. Some of these species, usually 

 secondary, when they become exceedingly numerous through favourable oppor- 

 tunities for breeding, do at times become primary and attack nearby healthy 

 timber to a varying degree, causing local sporadic outbreaks. Some of the more 

 important of these species have been mentioned in the preceding paragraph. 



A few of our species normally attack healthy trees in individual pairs, and 

 while their young may succeed in developing, only the part of the tree directly 

 affected receives any serious injury. Dendroctonus valens Lee., the Red Turpen- 

 tine Bark-beetle, often kills patches of bark at the base of pine and spruce without 

 killing the trees outright. This species is responsible, however, for the death of 

 considerable numbers of yellow pines in British Columbia, and is an important 

 assistant of the Western White Pine Bark-beetle and the Western Pine Bark- 

 beetle in the epidemic outbreaks. 



Several species of Pityophthorus kill twigs of pines in considerable numbers. 

 Species of Phloeosinus and Eccoptogaster cut food tunnels in the twigs of their 

 host trees, causing more or less injury thereby. 



Several secondary species of the genera Polygraphus, Eccoptogaster, Pityo- 

 genes, Pityophthorus, and others, hasten the death of the lower branches of pine 

 and spruce, and to that extent may in a sense be considered beneficial in helping 

 to produce cleaner trunks and, therefore, better logs. 



NEUTRAL SPECIES. 



Many bark-beetle species are found breeding only in dying bark and are 

 not known to cause any injury to living trees. Leperisinus aculeatus Say, in 

 ash; Chramesus icorice Lee., in hickory; Hylurgopinus rufipes Eichh., in elm; 

 and Pseudopityophthorus minutissimus Zimm., in branches of oak and beech, are 

 not known to injure living trees in our woods. Lymantor decipiens Lee., and a 

 few others, breed in dead bark and sapwood. 



THE IMPORTANCE OF BARK-BEETLE INJURIES IN CANADIAN FORESTS. 



These injuries include the normal annual loss to weakened trees, minor 

 sporadic outbreaks, and the extensive epidemic outbreaks. 



THE NORMAL ANNUAL LOSS. 



In addition to the more evident outbreaks where large numbers of trees die 

 each year in the infested area, there is a very large and often unrecognized annual 

 loss due to the normal activities of forest insects. Everywhere throughout the 

 forest, injured, unthrifty, and overmature trees are attacked and killed by 



