Ss 
Courtesy Can. For. Serv. Courtesy Can. For. Serv., 
Figure 193.—Larvae of the Gt. Lakes For. Res. Cent. 
mountain-ash sawfly, Figure 194.—Larvae of the 
Pristiphora geniculata. yellowheaded spruce sawfly, 
Pikonema alaskensis. 
late-stage feeding larvae and cocooned populations (607, /202). An attractant 
involving female and synergistic host components has recently been identified (60, 
61). 
The greenheaded spruce sawfly, P. dimmockii (Cresson), is recorded from 
Newfoundland to Northwest Territories, New Hampshire, Colorado, Wyoming, 
and Idaho, and feeds on various species of spruce. Populations are usually low and 
apparently cause little injury. 
The willow sawfly , Nematus ventralis Say, occurs in southeastern Canada, south 
to Georgia, and west to Utah, Colorado, and Montana. Its favored host is willow, 
but it also feeds on poplar. Full-grown larvae are black or greenish-black, with large 
light-yellow spots on the sides of the body, and are about 18 mm long. 
Winter is spent in the prepupal stage in cocoons in the litter or topsoil beneath the 
trees. Pupation and adult emergence occur in the spring. Eggs are deposited in 
pockets cut in the tissues of the leaves. Young larvae feed in colonies, eating small 
holes in the leaves. Later, entire leaves are eaten. There may be one to several 
generations per year, depending on location. Some individuals may remain in 
diapause up to 20 months before completing their development, especially in 
northern areas. 
The willow sawfly occasionally heavily defoliates willows in ornamental plant- 
ings and along streams. Basket willows in the South have been damaged severely. 
Nematus salicisodoratus Dyar occurs from Maine to Virginia, west to Wiscon- 
sin, Illinois, and Arkansas. It also feeds on willow and poplar. Full-grown larvae are 
light green and about 15 mm long. The head is black and there are three longitudi- 
nal rows of closely spaced black spots on the dorsum. There are also two rows of 
black spots on each side; those in the lower row are larger. Winter is spent in the 
prepupal stage in cocoons on the ground. Pupation occurs in the spring, and adults 
405 
