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. 



(PI. 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 in 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 five under "spike tops" and in knobby branches on certain 



1 Identified by H. G. Dyar. 



