38 



BULLETIN 1490, U. S. DEPARTMENT OF AGRICULTURE 



The wood of trees that have been infested by larvae of 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. This moth is especially abundant ; in south- 

 eastern Montana a large percentage of the trees are pitch-soaked. 

 For this reason the lumber is utilized only as rough lumber for 

 sheds and similar structures where shrinkage can be discounted (5). 

 Serious damage by this moth can be lessened by clean forest man- 

 agement. 



"Pitch seams," "gum check," or whatever these defects may be 

 termed locally, have always been recognized as a serious depreci- 

 ating factor in the utilization of Douglas 

 fir (4). 



The loss is occasioned by the work of 

 the Douglas fir " pitch moth," 33 which 

 causes the difference in price between abso- 

 lutely clear lumber and the lower grades 

 or dimension stuff. These insects work in 

 the portions of the trunks of living trees 

 which later clear themselves of branches; 

 hence only those logs are affected which, 

 were it not for previous infestation by the 



moths, would vield the better 



grades 



of 



lumber. 



Sawyers of Douglas fir estimate a gen- 

 eral loss in the entire Douglas fir product 

 of between 7.5 and 15 per cent due to this 

 defect of pitch seams in the logs used (4). 

 The depreciation is lowest in the Rocky 

 Mountain region and heaviest toward the 

 Pacific coast. Such pitch pockets are not 

 always caused by insects. 



Another pitch moth, the Sequoia pitch 

 moth, 34 greatly retards the growth of lodge- 

 pole pine in western Montana (3). 



Under present forestry conditions in this 



country it is impracticable to control these 



insects over large areas. 



Similar defects due to the working of the larvae of moths and 



flies 35 (fig. 39) in pitch near insect wounds or other wounds, occur 



in all sections of the country. 



Fig. 41. — Black check, in 

 western hemlock, radial 

 section. (6) 



DEFECTS CLASSED AS GUM SPOTS OR STREAKS 



" Gum spots " in western hemlock 36 and Douglas fir 3r are caused 

 by insect attack. 



Gum spots entail practically no loss to mills, nevertheless they 

 cause losses to the builder and consumer. Gum-spot defects are also 

 due to causes other than insects. 



33 Sesia novaroensis Hy. Edw. 



34 Vespamima sequoia Hy. Edw. 



35 Cheilosia spp. 



36 Melanophila drummondl Kirby causes this defect in both hemlock and Douglas fir 

 (fig. 40). 



37 The pitch moth (Pinipestis zimmcrmanni Grote) is responsible for not more than 10 

 per cent, Dendroctonus pseiidotsugae Hopkins for not less than 70 per cent, and all 

 other causes for about 20 per cent of the damage. 



