CIRCULAR 864. U. S. DEPARTMENT OF AGRICULTURE 



Figure 3. — Evidence of a western pine beetle epidemic in progress. Dying and dead 

 ponderosa pines with their characteristic sorrel or red foliage, showing white 

 in this picture, stand out in sharp contrast in a normally green forest. 



ward. For several months after a tree lias been attacked, the needles 

 are of a sickly green or yellow cast, later becoming red or reddish 

 brown. The third year after attack about 80 percent of the needles 

 drop from the tree, and after the fifth year practically all the needles 

 have been lost. 



Fading foliage is an important aid in locating centers of western 

 pine beetle infestation and in identifying dead trees, bnt it is not 

 altogether a reliable means, because trees attacked by other bark 

 beetles also have fading foliage. However, the fading of the foliage 

 from western pine beetle attack progresses much more rapidly and 

 uniformly than that caused by most other insects. 



Whether an attack by the western pine beetle has been successful 

 can best be determined by examining the bark of a suspected tree. 

 If the attack has been successful, small amounts of fine yellow or 

 reddish borings will be lodged in the crevices of the bark or deposited 

 on the ground around the base of the tree. These borings are pushed 

 from the tree through ventilation holes about one-sixteenth of an 

 inch in diameter, made by the attacking beetles. Around or closing 

 the point of entrance of a pair of beetles will usually be found pink 

 or red pitch in the form of a small tube. Trees lacking in vigor or 

 trees that are heavily attacked usually produce inconspicuous "pitch 

 tubes,'" but on some trees no pitch tubes are produced. 



The real evidence of a devastating attack by the western pine beetle 

 is found by removing a section of bark. If a maze of criss-crossing 

 tunnels (fig. 4), tightly packed with reddish borings, is found wind- 

 ing through the cambium layer, the tree is doomed. These tunnels 

 are the egg galleries constructed by the adult beetles, and their 



