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.t. 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 lable. 
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 Inlled. 
In Wyoming and Colorado the most common insect enemy of lodge- 
pole pine is the lodgepole pine beetle (Dendroctonus murrayanae 
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: 
