THE WESTERN PINE BEETLE 3 



curved, wrinkled, legless, brown-headed grub, and when mature is 

 about one-fourth inch long. The pupa (fig. 2, 6'), or resting stage, 

 during which the transformation to the adult form takes place, is also 

 white. All the appendages of the adult beetle can be recognized on 

 the pupa. The adult beetle (fig. 2, D) is brown to black, cylindrical, 

 rather stout, and is from one-eighth to one-fourth of an inch lonir. 



Figure 2. — The four stages of the western pine beetle: A, Eggs; B, larva; 

 C, pupa; D, adult. Each 8 times natural size. 



WORK AND HABITS 



The western pine beetle attacks and breeds primarily in ponderosa 

 pine (Pinus ponderosa Lawson) and Coulter pine (P. coulteri D. 

 Don.). It has been an inhabitant of the pine forests throughout its 

 present range for hundreds of years. 



In an examination of a dead or dying ponderosa pine tree, the real 

 killers, the western pine beetles, often escape detection because they 

 are concealed within the outer corky bark or have completed their 

 development and emerged. The large grubs or beetles commonly 

 found between the bark and wood of these trees are of other species 

 and of only secondary importance. One or more species of pine en- 

 graver beetles (Ips spp.) and flatheaded borers (Melanophila spp.) 

 are sometimes found in the upper part of a tree, and the red turpentine 

 beetle (Dendroctonus vol ens Lee.) sometimes attacks the base before 

 the western pine beetle begins its assault. The interrelationship of 

 these insects is complicated, but the western pine beetle is primarily 

 responsible for the death of the trees it attacks. 



How to Recognize an Attack 



The western pine beetle attacks only the main trunks of trees with 

 bark sufficiently thick to protect its various stages through their 

 development. It does not breed in limbs or small tops, and seldom 

 attacks trees under 6 inches in diameter. 



Upon entering a ponderosa pine stand or viewing a forest from 

 an observation point, one can readily detect the presence of the west- 

 ern pine beetle by differences in the color of the foliage of green and 

 infested trees (fig. 3). The needles of infested trees fade rapidly 

 and progressively from green through the yellows to a red, finally 

 turning sorrel, or reddish brown. They die from the center of the 

 needle cluster outward and usually from the top of the tree down- 



