6 BULLETIN 295, U. S. DEPARTMENT OF AGRICULTURE. 
considerable numbers. However, the relation seems to be of no 
economic importance. 
In Montana and Idaho another species of Pinipestis, P. cambiicola 
Dyar, 1 is one of the most important factors in regard to the existence 
of Pinipestis zimmermani Grote. It infests during the latter part 
of June the cambium of the terminal branches of mature yellow 
pine, and many of these wounds are subsequently reinfested by 
the latter year after year. The work of this insect is almost invari- 
ably the primary cause of the knobby growth on branches in which 
the Zimmerman pine moth breeds undisturbed by woodpeckers or 
parasites, and this moth must therefore be regarded as a provider 
of brood trees for the more destructive Pinipestis zimmermani. 
(PL III.) 
RELATION TO NATURAL ENEMIES. 
In most sections of the Rocky Mountains the Rocky Mountain 
hairy woodpecker {Dryobates villosus monticola) is unquestionably 
the most efficient natural force in restraining the Zimmerman pine 
moth. Thousands of trees, are each year regularly infested by the 
moth in comparatively small areas, and this bird as regularly destroys 
almost all of the larvae in all of them during early winter, so that, 
although hundreds of trees may be examined at a time, it is only on 
rare occasions that larvae are found after December in wounds io the 
trunks of trees which had been infested during the previous summer. 
This woodpecker seems to have a decided preference for the cater- 
pillar of the pine moth wherever the writer and the entomological 
rangers assigned to the Northern Rocky Mountain Field Station have 
had opportunities for observation. In the extreme southeastern part 
of Montana, and particularly that portion covered by the Northern 
Cheyenne Indian Reservation' and by the- Custer National Forest, 
the moth has apparently neither bird nor insect enemies. In all other 
localities this woodpecker is fully able to eliminate this insect as a 
serious factor in timber destruction. Especially will the work of the 
bird become effective when the habits of the moth are more generally 
understood and its " brood trees" are eliminated through use by man. 
From reports from other field stations the writer concludes that 
from Idaho west toward the Pacific coast and in the southern Rocky 
Mountain region woodpeckers are of no consequence as a check upon 
this insect. But, considering that much confusion still exists con- 
cerning the identity of Pinipestis among the "pitch moths," this 
conclusion may prove erroneous when more thorough information is 
available. 
The woodpecker never molests the caterpillars of the pine moth 
which live under "spike tops" and in knobby branches on certain 
1 Identified by H. G. Dyar. 
