THE WESTERN PINE BEETLE 





Figure 4. — Proof of attacks hy western pine beetles. Egg galleries through the 

 cambium or inner bark are deep, frass-filled channels, and show on the sapwood 

 as tightly packed frass, which adheres to the surface of the wood. 



characteristic pattern may be regarded as the sign of the western 

 pine beetle. 



Method of Attack 



A few beetles cannot kill a tree. It has been estimated that a con- 

 centration of 12 pairs of beetles per square foot of bark surface, or 

 about 6,100 beetles, are required to kill an average-sized ponderosa 

 pine. It has been estimated further that enough new beetles are 

 ordinarily produced in a single infested tree to kill 5 other trees of 

 the same size. 



For all practical purposes, as soon as a few western pine beetles 

 have started their galleries the tree on which they are working may 

 be considered dead. When the beetles alight on the trunk of a tree, 

 they seek crevices in the bark and bore small round holes directly 

 into the cambium layer. If they encounter too copious a flow of saj) 

 or pitch, they may be drowned or "pitched out;" however, if the 

 flow of sap is weak, the beetles are able to continue their boring 

 through the cambium or vital growing layer of the tree. During 

 the summer months it takes only about 14 days for the western pine 

 beetle to kill an average-sized ponderosa pine. 



Attacks are begun by the female beetle, and she is joined by the 

 male about the time she reaches the cambium layer. The female 

 constructs practically the entire egg gallery, and deposits her eggs 

 singly in niches cut in the sides of the tunnel as it is being extended. 

 The female excavates about 28 inches of gallery, depositing about 

 65 eggs. In a normally attacked tree about 11 feet of tunnels are 

 made in each square foot of bark by the various pairs of beetles whose 



