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 sclivjarzi 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 
larvae 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 larvae, 
feeding on the strictly fresh cambium surrounding it, usually stop 
the necessary flow of sap 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 
nnwiiling, 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. I). Hopkins. 
2 Busck, August. Descriptions of new mierolepidoptera of forest trees. In Proc. Ent. Soc. Washington, 
v. 16, no. 4, p. 143-150, pi. 7-8, 1914. 
3 Identified by August Busck. 
