20 BULLETIN 154, U. S. DEPARTMENT OF AGRICULTURE. 



INSECTS. 



Although lodgepole pine in the Rocky Mountains has not suffered 

 severely from insect attack in recent years, bark beetles have un- 

 doubtedly killed more mature timber than has any other agency 

 except fire. In Montana the mountain pine beetle {Dendroctonus 

 monticolae Hopk.) has done some damage in the vicinity of Swan 

 Lake on the Flathead National Forest, and in 1911 an aggressive 

 attack by this beetle in the Big Hole Basin on the Deerlodge and 

 Beaver Head Forests developed serious proportions. 1 In that year 

 approximately 15,000 trees were killed on an area of about 1,500 

 acres. On some portions of the area practically all the trees over 

 5 inches in diameter were either killed or badly infested, while on 

 the remainder of the area the attack was confined to the larger and 

 less vigorous trees. The attack appeared to radiate from several 

 centers where the damage was particularly severe. It appears likely 

 that this infestation resulted largely from injury to the trees by 

 adverse weather conditions during the winter of 1908-9, the in- 

 sects taking advantage of the trees' weakened condition. The un- 

 usually dry summer of 1910 was also thought to have favored the 

 attack. Fortunately many of the insects were destroyed during the 

 winter of 1911-12, apparently by winter killing, to which the thin 

 bark of lodgepole renders them liable. 



In regions other than the one considered in this bulletin, damage 

 by the mountain pine beetle has been very severe. On the Wallowa 

 and Whitman National Forests in eastern Oregon it has recently 

 killed 100,000,000 board feet of lodgepole. Here the infested area, 

 which in 1906 covered only about a section, had by 1912 grown to 

 approximately 320,000 acres, and the beetle was then extending its 

 attack to yellow pine. 



The presence of the mountain pine bark beetle is first made evident 

 by pitch tubes, boring dust, and woodpecker work. Most of the 

 adult beetles emerge during August, and by early fall are well estab- 

 lished in their new hosts. The trees thus attacked usually remain 

 green until the following spring, when their tops first turn a yel- 

 lowish and then a reddish color. By the time the red-top condition 

 is reached practically all the beetles have left the tree. The species 

 apparently prefers to attack injured and felled trees; the more 

 vigorous, and particularly the younger trees, are often able to drown 

 the beetles in exudations of pitch. Thrifty trees, however, are some- 

 times killed. 



In Wyoming and Colorado the most common insect enemy of lodge- 

 pole pine is the lodgepole pine beetle {Dendroctonus rnurrayanae 



1 For a complete description of this and other bark beetles of the genus Dendroctonus, 

 together with methods of control, see Bureau of Entomology Bulletin 83, Part I, by 

 Dr. A. D. Hopkins. 



