INSECT ENEMIES OF WESTERN FORESTS 



135 



vertical, long, slightly to markedly sinuous. The larval mines are 

 usually in the cambium; pupation may take place either in the 

 inner bark or concealed in the outer corky bark. Normally there 

 is but one generation a year, and since the emergence is extended 

 throughout most of the season there are never any great numbers 

 of beetles attacking at any one time. The species is usually second- 

 ary and relatively unimportant. 



The Arizona pine beetle (Dendroctonus arizonicus Hopk.) at- 

 tacks and kills ponderosa pine and Apache pine in central Arizona 

 and probably other parts of the Southwest. Its appearance and 

 habits are very similar to those of the southwestern pine beetle, 

 and the methods of control are the same. 



The Colorado pine beetle (Dendroctonus approximatus Dietz) 

 attacks ponderosa, Arizona, and probably other pines in its range 

 from northern Colorado and southern Utah south through Arizona 

 and New Mexico. The dark-brown, elongate adults are from % to 

 about y 5 inch in length. They excavate a network of long, longi- 

 tudinal, diagonal, and sometimes transverse galleries between the 

 bark and wood of dying, felled, and occasionally of healthy trees. 

 The brood galleries are distinguished from those of most other 

 species by the fact that the eggs are deposited in large niches on 

 the side of the gallery farthest from the wood, rather than on the 

 other sides of the gallery. Its work is therefore characterized by 

 the absence of exposed larval mines on the inner surface of the 

 bark. There is only one generation annually, and as a consequence 

 it is not an aggressive species nor one of economic importance. 



The mountain pine beetle (Dendroctonus monticolae Hopk.) 



Figure 59. — Lodgepole pine stand killed by the mountain pine beetle. 



