THE ZIMMERMAN PINE MOTH. 9 
show a tendency to develop into tops, are reached and the trees 
killed, and on mature ones to a point where the thickness of the bark 
fails to suit the insect. (PL VIII.) 
On wounds infested by a single larva a pitch tube, resembling that 
produced by sesiid pitch moths, is usually formed, presumably because 
one larva alone is not capable of cutting as near the surface as when 
several work together in one space. In the latter case the tunnels 
cross and recross continuously, and when a larva strikes the tunnel of 
another, which must happen frequently, it usually' cuts to the surface 
in order to avoid the solidified pitch. To the presence of the larva 
so very near and even at the surface of the bark must be attributed 
its rather heavy parasitization in localities where its parasite exists, 
because larvae living singly are very seldom parasitized. 
EFFECT OF INFESTATION ON TREE GROWTH AND FOREST. 
It is obvious that the killing of many trees in stands preferred by 
the moth results in too great a thinning out of the stand. This 
wastage of ground is further augmented by the permanent stunt- 
ing of a still greater number of trees by the insect's work, because 
the space taken up by such scrubs would just as readily accommodate 
thrifty, well-formed trees. 
Moreover, the wood from trees that have been infested by the moth 
is invariably so permeated with pitch that the lumber cut from 
such logs is either materially reduced in value or is rendered wholly 
unfit for commercial use. (PL IX.) From one part of southeastern 
Montana, where this moth is especially abundant and a large per- 
centage of the trees are pitch soaked, the lumber is, for this reason, 
only used for sheds, etc., where shrinkage can be discounted; the 
users find it cheaper to have the better material shipped in than to 
pick it out of the local stuff and throw half of it away unless it is 
needed for the less particular purposes indicated. To the writer this 
practice at first seemed rather to indicate prejudice against the home 
product, because there is a large amount of first-grade lumber pro- 
duced along with the bad. However, the pine moth is responsible for 
this condition, as was abundantly proved by examination of its 
injury in the district. The manner in which the moth's work u pitch- 
ifies " the wood is best seen in the .well-known tops which have been 
infested by it. From these tops the bark has dropped off, but the 
surface of the wood has a roughened appearance and the tissues are 
literally saturated with pitch, while at the lower end, where the 
infestation ended and the wood was not pitehified in the process, the 
spike is rotted off from the tree. This insect's work alone accounts 
for the fact that the extreme top of a tree may be excessively pitchy, 
while the rest of the same tree is not. 
