DOUGLAS FIE PITCH MOTH. 6 



the seasonal history and habits of insects affecting the growth and de- 

 velopment of trees, though a number of caterpillars, of what later 

 proved to be this moth, had been caged during the autumn -of 1912 for 

 observation. Active cooperation in collecting larvae and field notes 

 with Messrs. Edmonston, Miller, Burke, Harvey, and all the entomo- 

 logical rangers assigned to the various western field stations from 

 April, 1913, until late autumn, 1914, made it possible to determine not 

 only the insect's distribution, but its comparative abundance and de- 

 structiveness in widely separated regions of the Douglas-fir range and 

 also to make this investigation pretty thorough west from the eastern 

 boundary of the State of Montana, toward the coast, and north cf 

 latitude 11° 30' to the boundary of the United States. 



LIFE HISTORY. 



THE ADULT. 



The Douglas-fir pitch moth, like all the members of the Sesiida?, 

 much resembles, in general appearance, certain wasps and flies. This 

 resemblance is especially strong when the insect is in flight. 



The ground color of the insect is black, with rich orange-red spots 

 on the thorax and with all the segments, except the last, banded with 

 the same color. Underneath the whole insect is rich orange-red. 

 Aberrations in color are not frequent but exist, as the rearing of a 

 wholly black female would indicate. 



The forewings are transparent, opalescent, with black borders and 

 prominent discal mark; the hind wings transparent, with slight discal 

 mark and narrow black margin. The spread of wings is from 30 to 

 '.j~> mm., about the size of an ordinary "yellow jacket.' 1 The male 

 is about one-third smaller than the female and more slender. 



THE EGG. 



The eggs are brownish, slightly oblong, and are laid singly. A 

 single female appears to produce slightly in excess of 30 eggs, the 

 issue from two specimens being 34 and 37, respectively. In the field 

 their incubation period is about two weeks. 



THE LARVA. 



With the exception of the head, which is dark brown, the larva (fig. 

 1) is white: through die transparent skin the darker intestines and 

 their contents are plainly visible, thus making this larva readily dis- 

 tinguishable from that of Vespamima sequoia Ily. Edw., which, to a 



slight extent, also infests Douglaf fir. hut which is more robust, has a 



denser skin, and is dirty white. Especially is this internal dark spot a 



feature in 1 and - year old Larvee, although it is retained to a marked 



