INSECT ENEMIES OF WESTERN FORESTS 107 
cent of the stand may be killed over large areas (fig. 53). Under 
such conditions it shows little discrimination and will attack and 
kill trees of all sizes, except the very smallest, apparently without 
regard for their health or vigor. Infested groups may contain from 
2 or 3 to as many as 350 or more trees, and the size of the groups 
is a good indication of the severity of the infestation. On the edge 
of large groups there will nearly always be “pitched-out” attacks, 
indicating insufficient numbers in the attacking force. While pon- 
derosa pine is the favored host, the beetles, particularly when epi- 
demic, will attack ali other pines within their range, such as lodge- 
pole, limber, bristlecone, Mexican white, and pifion pine, and occa- 
sionally spruce. This beetle is so similar to the mountain pine 
beetle in appearance, habits, and the character of work as to be 
scarcely distinguishable from it. 
The Black Hills beetle passes the winter as young to full-grown 
larvae and parent adults under the bark of trees attacked the pre- 
vious season. The new brood of mature adults emerges late in July 
and in August, with some stragglers emerging in September. There 
is but one generation a year. 
Direct control methods consist in felling the infested trees and 
peeling the bark or decking trees into piles and burning them. This 
work is usually done late in the spring and early in the summer. 
Peeling becomes ineffective as soon as the pupae have formed. 
Burning can be carried on later, but it will be halted by the approach 
of fire weather. ; 
The Jeffrey pine beetle (Dendroctonus jeffreyi Hopk.) is an 
ageressive and at times very destructive enemy of Jeffrey pine in 
California. Although it often attacks trees that are apparently in 
a healthy condition it seems to prefer trees that are retarded in 
growth by droughts or defoliations. It rarely attacks felled trees, 
so does not breed in slash or windfalls to any extent. It confines 
its attacks to Jeffrey pine, and its distribution is therefore limited 
to that of its host tree. 
The work of this beetle (fig. 54) 1s very similar to that of the 
mountain pine beetle. Reddish pitch tubes form at the mouth of 
the entrance holes, which are usually in crevices of the bark. There 
is usually a shght turn at the bottom of the egg gallery, which 
then proceeds up the tree in nearly a straight line following the 
grain of the wood. These galleries are usually 2 or 3 feet in length 
and are packed with boring dust. The eggs are placed in niches 
along the sides of the galleries, and the larvae work out from the 
egg gallery across the grain of the wood. The pupal cells are 
formed in the inner bark and are exposed to view when the bark is 
removed. The adults are black and about one-fourth of an inch 
in length, similar to, but considerably larger than the mountain 
pine beetle. 
Trees are attacked most frequently in July or August. Eggs are 
laid, and some of the insects reach the new adult stage by winter. 
Parent adults, larvae, and new adults spend the winter under the 
bark. In the spring, development continues, and most of the new 
broods emerge during July and August. Thus there is ordinarily 
only one generation a year. 
PA. Cee wee ee 
