THE ZIMMERMAN PINE MOTH. 5 



within a period of two years has in all cases proved to be exactly 29 

 days. 



Eggs laid the previous autumn hatch in early spring and develop 

 into adults during August and September of the same year, while 

 eggs deposited during May evidently develop into adults early the 

 following spring. 



RELATION TO OTHER INSECTS. 



In the northern Rocky Mountain region Pissodes schwarzi Hopk. 1 

 is a common associate of the pine moth in yellow pine, if the trees 

 are attacked near the base. It appears that there the moth takes as 

 frequent advantage of the work of the beetle as the beetle does of 

 the moth's. The result of infestation by either of them is exactly 

 alike, although the latter's attack is by no means restricted to the 

 base of trees, while the work of the beetle is rarely found more than 

 2 or 3 feet above ground. 



Sesia brunneri Busck, 2 wherever it exists (at present known in 

 Montana and southern Idaho), is frequently associated with Pinipestis 

 in yellow and lodgepole pine. While the attack by the Sesia in 

 lodgepole pine appears to invite and to be the cause of subsequent 

 infestation by the Pinipestis, the former frequently takes advantage 

 of the work of the latter in yellow pine greatly to augment its own 

 numbers. When this sesiid moth attacks a tree primarily it inva- 

 riably deposits but one egg at a spot; but when it infests the pine 

 moth's work in yellow pine it seems always to deposit quite a number 

 of eggs. The writer has taken as many as six nearly mature Sesia 

 larvse from a single space surrounding a spot previously infested by 

 the pine moth. The space infested by the latter is always killed and 

 subsequent infestation can only occur at the border of such a spot. 

 As the Sesia larva works parallel with the grain of the wood, its 

 infestation of Pinipestis work becomes evident on the surface of the 

 surrounding fresh bark by regular pitch masses of the size of a silver 

 dollar instead of the general pitchiness which characterizes pine pest 

 infestation, owing to the numerous holes it makes in the bark. 



If the pine moth reinfestc such a Sesia-infested space, its larvse, 

 feeding on the strictly fresh cambium surrounding it, usually stop 

 the necessary flow of s-ap to the space occupied by the Sesia and the 

 latter is starved to death on this account. To comprehend how this 

 is possible, it must be understood that the sesiid larva is not able to 

 move around at will on the surface of the bark, that it is apparently 

 unwilling, if not unable, to cross spaces already sapped by other 

 insects, and that it requires two years to complete its life cycle. 



Two small moths of the genus Laspeyresia, 3 one in yellow pine and 

 one in Douglas fir, frequently breed in the work of the pine moth in 



i Identified by A. r>. Hopkins. 



2 Busck, August. Descriptions of new microlepidoptera of forest trees. In Proc. Ent. Soc. Washington, 

 v. 16, no. 4, p. 143-150, pi. 7-8, 1914. 



3 Identified by August Busck. 



