INSECT ENEMIES OF WESTERN FORESTS 1Q7 



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 w^ithout 

 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 wdll 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, wall attack all other pines wdthin their range, such as lodge- 

 pole, limber, bristlecone, Mexican white, and pihon pine, and ocx^a- 

 sionally spruce. This beetle is so similar to the mountain pine 

 beetle in appearance, habits, and the character of w^ork as to be 

 scarcely distinguishable from it. 



The Black Hills beetle passes the winter as young to full-grow^i 

 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, wdth 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 w^ill be halted by the approach 

 of fire weather. 



The Jeffrey pine beetle {Dendroctonus Jeffrey i Hopk.) is an 

 aggressive 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) is very similar to that of the 

 mountain pine beetle. Reddish pitch tubes form at the mouth of 

 the entrance holes, wdiicli are usually in crevices of the bark. There 

 is usually a slight turn at the bottom of the e^g 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 

 ^gg gallery across the grain of the w^ood. 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. 



