INSECT ENEMIES OF WESTERN FORESTS 139 



f ested timber, particularly whether the trees are thin-barked, such 

 as lodgepole pine, or thick-barked, as sugar pine. The more com- 

 monly used methods include (1) felling the infested trees and 

 burning the bark either on or off the trunk; (2) felling trees and 

 peeling the bark to expose the immature broods; (3) felling 

 and sun-curing; (4) spraying trees with fuel oil and burning them 

 either after felling or while standing; and (5) spraying trees with 

 penetrating petroleum oils to which a toxicant such as orthodi- 

 chlorobenzene, DDT, benzene hexachloride, or chlordane has been 

 added, either after felling or while the trees are still standing. 



For sugar pine the usual method is felling, peeling the top half 

 of the log, and burning the lower half. Burning can be continued 

 until the start of emergence or until the fire hazard becomes too 

 great. Peeling can be used on white pine, the bark of which slips 

 easily; but peeling becomes ineffective after the broods start to 

 pupate. Nearly all methods are applicable to treatment of lodge- 

 pole pine. In the southern part of its range broods can be destroyed 

 with the sun-curing method by felling the trees, trimming off the 

 branches, and exposing the trunk to the sun's rays ; then, after a 

 few days' exposure, rolling the logs to expose the under half. 

 Control operations for the mountain pine beetle are usually under- 

 taken in the spring. 



The Black Hills beetle (Dendroctonus ponderosae Hopk.) (9, 10, 

 11, lb) is the most aggressive and destructive insect enemy of 

 ponderosa pine in the Rocky Mountain region. It is distributed 

 from the Black Hills of South Dakota to eastern Montana and 

 south through eastern Wyoming, Colorado, Utah, Arizona, and 

 New Mexico. Under normal conditions it is comparatively rare 

 and found only in weakened, decadent trees. Periodically, how- 

 ever, its numbers increase to epidemic proportions and these 

 sweep through the ponderosa pine stands, killing small to large 

 groups in ever-increasing numbers, until as much as 50 to 90 

 percent of the stand may be killed over large areas (fig. 62). 

 Under such conditions it shows little discrimination and will 

 attack and kill trees of all sizes, except the very smallest, appar- 

 ently 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 ponderosa pine is the favored host, the 

 beetles, particularly when epidemic, will attack all other pines 

 within their range, such as lodgepole, limber, bristlecone, and 

 pinyon, and occasionally spruce. This beetle is so similar to the 

 mountain pine beetle in appearance, habits, and character of 

 work as to be scarcely distinguishable from it (fig. 61). 



The Black Hills beetles pass 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 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 of (1) felling the infested trees 



