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



originally made by Sesia novaroensis, thus extending the injury. In 

 Montana it infests wounds in the trunks of Douglas fir to the extent 

 of about 1 per cent. But in the vicinity of Ashland, Oreg.. Vespa- 

 mima appears to have developed a special liking for this tree. Fully 

 10 per cent of the pitch-moth larvae sent me by Messrs. Edmonston 

 and Miller from Ashland proved to be Vespamima sequoia. Accord- 

 ing to the accompanying notes, all of the larvae of this species were 

 collected in wounds previously made. At Placerville, Cal., a single 

 larva of Vespamima was collected in Douglas fir. and this was in an 

 old wound. 



Wounds in Douglas fir, especially those made by the pitch moth, 

 presumably on account of their better protective character, are 

 usually infested for several seasons by the larvae of a small moth of 

 the genus Laspeyresia. 1 Two or three larvae are frequently found 

 around the edges of a single wound. The Laspeyresia also attacks- 

 young Douglas fir at the base of branches independently, and, 

 although the attack itself usually does no permanent injury, the 

 resulting accessibility to the cambium often induces infestation by 

 the Sesia. That the work of Sesia is responsible for the increasing 

 numbers of Laspeyresia, by providing favorable conditions for prop- 

 agation, seems a reasonable conclusion, yet it is doubtful if the 

 abundance or scarcity of Laspeyresia similarly affects the pitch moth, 

 which is well able to establish and sustain itself. 



RELATION TO NATURAL ENEMIES. 



In localities where Sesia novaroensis is more than commonly 

 numerous nearly 20 per cent of its larvae are killed before reaching 

 maturity by a tachinid parasite. 2 The influence of this parasite 

 as a check on the numbers of Sesia or as lessening the depreciation 

 of timber appears from a strictly economic standpoint to be practi- 

 cally nothing, since it appears from extensive observations that only 

 those moth larvae under imperfect pitch tubes are subject to attack 

 by the parasite. As the greater number of pitch tubes form an 

 impenetrable barrier against the parasite, there is little reason to 

 expect that it will ever be a factor in the control of the pitch moth. 



MEANS OF CONTROL. 



In determining control measures for use against the Douglas fir 

 pitch moth five readily accessible areas were selected for detailed in- 

 vestigations. On all of these the stand of timber was mixed and the 

 conditions were those which obtain in almost any location west of 

 the Rocky Mountains, excepting the pure pine stands. The results 



1 Identification by August Busck, Bureau of Entomology. 



2 Identification by C. T. Greene, Bureau of Entomology. 



