DOUGLAS FIR PITCH MOTH. 17 
usually indicates the presence of the larva. Plural infestation un- 
der one pitch tube has not as yet been observed. 
It is only upon very close examination of the tree that the infesta- 
tion will be revealed, so perfect is the blending of color of the Doug- 
las-fir pitch and the bark, notwithstanding the fact that the covering 
pitch tubes are about 2 inches in diameter and protrude at least 1 
inch from the surface of the bark. The protuberances so much re- 
semble a knobby growth that considerable experience is necessary 
to enable one to distinguish them at sight. 
The attack is restricted to the main trunks of trees, the first, 
second, third, and fourth logs being usually most affected, the injury 
becoming notably absent above 60 feet from the ground. 
Trees are never killed outright, although very vigorous trees, if 
attacked several seasons in succession, become so weakened that their 
originally less robust neighbors easily outgrow them. 
RELATION TO OTHER DESTRUCTIVE INSECTS. 
In most localities where the Douglas fir pitch moth is present 
_ Douglas fir and larch trees are to be found with dead bark on the 
trunks in strips several inches wide and often more than 20 feet 
long. This peculiar injury, except in the case of Tetropium in larch, 
is usually attributable primarily to fires, bruises by falling trees, and 
perhaps, to some extent, lightning. Examination of these strips 
under the bark usually reveals sesiid larva, or at least abundant 
traces of their work. The galleries under the bark contain, in addi- 
tion, the unmistakable evidence of beetle infestation. In all such 
cases coming under the writer’s observation these beetles of the 
genera Melanophila or Tetropium were found to have infested the 
trees primarily or after they had sustained the mechanical injuries 
before mentioned, and to have been the agents which prepared favor- 
able propagating places for the moth. Extended observations lead 
the writer to believe that these and similar beetles do not follow the 
moth, but that the moths occasionally adopt the galleries, etc., of the 
beetles. 
A few trees which had been outstripped by their companions, evi- 
dently on account of previous moth infestation, were noted as subse- 
quently killed by Scolytus unispinosus, but, considering that these 
trees when killed by the beetles were already worthless as timber 
producers, the interrelation of moth and beetle in this instance seems 
of no economic consequence. 
Vespamima sequoia’ is another very injurious pitch moth which 
infests Douglas fir in old wounds and branches, and especially wounds 
+ Brunner, Josef, The Sequoia pitch moth. U.S. Dept. Agr., Bul. 111, 11 p., 5 fig., July 
11, 1914. 
