22 BULLETIN 255, U. S. DEPARTMENT OF AGRICULTURE. 



On account of the long life cycle of the Douglas fir pitch moth its 

 elimination, in any country where forestry is sufficiently advanced to 

 be a profitable business and where the forests are taken care of as 

 they should be in order that they may be profitable, will follow. In 

 the range of the Douglas fir there are millions of acres of forest land 

 which are inaccessible and practically worthless at the present day, 

 but they will remain so not much longer, and with advanced methods 

 in forestry Sesia nocaroensis is bound to disappear ultimately. The 

 process of its eradication will necessarily be slow, but this is no reason 

 why a systematic policy to attain this result should not now be 

 adopted in areas which have been and are being logged and which, it 

 is certain, will be logged again when the reproduction attains mer- 

 chantable size. 



While in this paper only the more serious result of pitch-moth 

 infestation during the first 40 years' growth of trees is considered, it 

 does not mean that the insect does no damage in older and mature 

 trees. As is seen under " Host trees," it infests these also under 

 favorable conditions, but in such cases the infestation results only in 

 the so-called " gum spots," the pitch blisters being too near the 

 surface of the trees to cause serious breaks and ultimate " pitch 

 seams" by mechanical strain in the part of the tissues rendered in- 

 flexible. In regard to the " gum spots " in Douglas fir, which entail 

 practically no loss to mills, but for which the builder and consumer 

 foots the bill entirely, the pitch moth is responsible for not more 

 than 10 per cent, Dendroctonus pseudotsugae for not less than 70 per 

 cent, and all other causes for about 20 per cent of the damage. 



