INSECT ENEMIES OF EASTERN FORESTS BG 
The full-grown larva of the yellow-headed spruce sawfly (Pi/o- 
nema alaskensis (Roh.)) is about 84 inch long and has a chestnut- 
brown head. The body is dark yellowish green above and hghter 
beneath, and is marked with a double gray-green longitudinal stripe 
down the middle of the back, another broad one which sometimes is 
more or less divided into a double stripe on each side, a broad darker 
lateral or subspiracular stripe, and a linear spot near bases of the legs 
on all but the last three segments. This species is distributed from 
Alaska and British Columbia to Wyoming, and east to New Bruns- 
wick, Quebec, and the New England States. Nash (3/7) gave an ac- 
count of its habits in the Maine forests. Its food plants include white, 
red, black, Norway, Colorado blue, and Engelmann spruces. The new 
foliage is preferred until the larvae are about half grown, and in 
Maine open growth in plantations and natural reproduction was most 
severely attacked. Heavy infestations seldom occur in stands with 
a closed canopy. There is one generation annually. 
The adults emerge in May or early in June and the eggs are deposited 
between the new needles as soon as the bud scales are cast off. Hatch- 
ing takes place in 6 to 8 days, and the larvae become full grown after 
a feeding period of 30 to 40 days. The cocoons are 24 to 14 inch long; 
dark brown, rough, with one end rounded and tapered to a blunt point 
at the other end. They are spun in the mineral soil beneath the trees 
in July, but pupation does not take place until spring. For control 
measures see page 544. 
The green-headed spruce sawfly (Pii:onema dimmockii (Cress.) ) 
has been reported in Canada from Labrador to the Pacific coast, and 
in many of the Northern States from Maine to Idaho. It feeds on 
various species of spruce, but apparently never becomes abundant 
enough to cause serious defoliation. 
The larva of the willow sawfly (Pteronidea ventralis (Say) ) is 
black or greenish black with a row of large yellow spots on each side 
of the body, the spots becoming lighter ‘and the body a slate black 
when the larva is full grown. It is then about 34 inch long (fig. 163). 
Figure 163.—Larvae of Pteronidea ventralis on a willow leaf. About X 2. 
792440°—49 37 
