2 CIRCULAR 8 6 4, U. S. DEPARTMENT OF AGRICULTURE 



sidered merchantable, because the western pine beetle has already 

 reduced the value of the commercial timber 60 to 90 percent (fig. 1). 

 During recent years losses caused by this beetle have been much less 

 severe ; however, the annual drain on our remaining forests is still of 

 such magnitude as to cause real concern to timber owners and con- 

 servationists. 



Beetle-killed trees deteriorate rapidly and soon become a total loss 

 to the lumberman. Practically all such trees are left in the forest as 

 snags. Until they fall and ultimately rot on the forest floor, these 

 snags add to the ever-present fire hazard in pine-growing regions. 



Figure 1. — A ! beetle-ravaged stand of ponderosa pine. Ghostly snags are mute 

 evidence of an invasion by the western pine beetle. More than 150 years of 

 unmolested growth will be needed before the reproduction in the center fore- 

 ground replaces the commercial stand killed by the beetles. 



Fortunately, the forests themselves, through normal annual growth, 

 oli'set part of this terrific drain. However, the new growth is of much 

 lower quality because it is mainly in immature trees, whereas losses 

 caused by beetles usually occur in mature and overmature trees con- 

 taining wood of high quality. Annual growth may compensate for 

 beetle-caused losses over a long period, but during the last two decades 

 it has been equal to only one-third of the annual drain from all causes. 



THE BEETLE 



The western pine beetle, in common with other beetles, has four 

 distinct stages (fig. 2) in its life cycle. The stage that may be ob- 

 served in an infested tree depends on the season and the time that 

 elapsed after the attack. The egg (fig. 2, A) is white, oval, and 

 about the size of a lead-pencil point. The larva (fig. 2, B) is a white, 



