8 BULLETIN 295, U. S. DEPARTMENT OF AGRICULTURE. 



stand of second growth. Yellow pine, lodgepole pine, and Douglas 

 fir are the tree species thus far noted to be subject to infestation by 

 this insect in the West. Out of a hundred trees so infested about 80 

 per cent are yellow pine, 15 per cent lodgepole pine, and 5 per cent 

 Douglas fir. Trees with a thick layer of fresh bark and cambium, as 

 well as the more vigorous growers, are preferred for attack. All 

 sizes, from but a few inches to several feet in diameter, are subject to 

 infestation; but it is the mature trees which furnish the most favora- 

 ble means of existence for this moth, while in the smaller ones, up 

 to about a foot in diameter, it does the greater damage. (PI. V.) 



CHARACTER OF INJURY AND WORK OF LARVAE. 



The moth, as a rule, attacks mature trees from between 10 to 30 

 feet from the top down, and second growth from about breast high 

 up to from 35 to 40 feet. Infestation nearer the top or base occurs 

 only to a very limited extent. 



As stated under "Seasonal history" (p. 4), fresh infestation is 

 only indicated by the castings on the surface area of the attacked 

 trees. If this area is very heavily infested, as in the case cited above, 

 where the writer found 27 nearly mature larvee in a space less than 

 5 feet in length by about 1 foot in width, there is at no time any other 

 indication observable. The bark dries up without exuding pitch, as 

 if scorched by extreme heat, and several years after the insect has 

 vacated the bark drops off and the injury becomes manifest to the 

 average passer-by. Usually, however, in such cases some larvae 

 leave the point originally infested and bury themselves higher up 

 near a branch of the same tree. The pitch tube at the entrance of 

 this tunnel invites close examination of the entire tree, whereupon the 

 less conspicuous, yet heavy infestation is almost sure to be detected. 

 (Pis. VI and VII.) 



During the spring following infestation drops of pitch usually 

 begin to ooze out of the tunnels in the bark and cover the surface of 

 the average wound with a uniform, thin layer, somewhat similar in 

 appearance to a liberal application of paint with a brush. The inner 

 bark assumes a spongy appearance and gains in thickness, which 

 tightens and even breaks the outer bark, together with the dried pitch 

 covering it. The entire infested space finally presents a strikingly 

 rough aspect which resembles the injury of no insect except Pissodes 

 schwarzi, which produces a similar effect at the base of trees. 



By repeated infestation at the border of the wound, in the course 

 of years the tree is gradually girdled and the part above the collar dies 

 and finally rots off at its base, provided the moth abandons the tree 

 at this stage. But frequently infestation continues downward, on 

 young trees usually until the lower branches, which by that time 



