106 



MISC. PUBLICATION 273, U. S. DKPT. OK AORK'ULTURE 



_ Direct control methods consist in felling the infested trees and 

 either peeling the bark from the trunk or burning the bark either 

 on or off the trunk. In the southern part of its range effective 

 destruction of the broods in thin-bark lodgepole pine can be secured 

 by felling the trees, trimming off the branches, and exposing the 

 trunks to the sun's rays. Under certain conditions spraying the 

 standing trees with fuel oil and burning them without felling has 

 been found to be inexpensive and effective. Control operations are 

 usually undertaken in the spring of the year. Peeling must be dis- 

 continued Avhen the broods pupate. Burning can be continued until 

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



Figure 5;i. 



-Severe damage to ponderosa pine in the Kaibab National Forest, Ai'iz., from 

 attack by the Black Hills beetle. (Blackman.) 



The Black Hills beetle {D end r act onus ponderosae Hopk.) {6) 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 (Avhence it received its name) to eastern 

 Montana and south through eastern Wyoming, Colorado, Utah, 

 Arizona, and I^ew Mexico. Under normal conditions it is compara- 

 tively rare and found only in weakened, decadent trees. Period- 

 ically, however, 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 per- 



