The willow sawfly, Nematus (=Pteronidia) ventralis Say, oc- 
curs in southeastern Canada and south and west in the Eastern 
States to Georgia 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 
top soil beneath the trees. Pupation and adult emergence occurs 
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 are usually one 
to five generations per year depnding on location. In the northern 
areas some individuals may remain in diapause up to 20 months 
before completing their development. 
The willow sawfly occasionally heavily defoliates willows in or- 
namental plantings and along streams. Basket willows in the 
South have been damaged severely. 
Nematus salicisodoratus Dyar occurs in the Eastern States 
west to Illinois. 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 longitudinal 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 of the first generation appear in late May 
or June. Larvae of this generation are found in June and July. 
Adults of a second generation appear from late July to early 
September. This species is often abundant locally in the North- 
eastern States. 
Approximately 40 additional species in the genus Nematus 
have been recorded from eastern forests (Muesebeck, et al.). 
Known hosts of a few species are as follows: black locust—N. 
abbotti (Kirby) and N. tibialis Newman, white birch—WN. hya- 
linus (Marlatt) and N. pinguidorsum Dyar, poplar—N. fulvicrus 
Provancher and N. populi (Marlatt), hophornbeam—WN. ostryae 
(Marlatt), and willow—N. limbatus Cresson. 
Trichiocampus irregularis (Dyar) occurs in southeastern Can- 
ada and southward through the New England States, and feeds 
on willow. Full-grown larvae are yellow, sparsely clothed with 
hairs, and about 18 mm. long. The head is almost entirely black 
and there are two rows of black spots on each side of the body. 
The related species, T. gregarius Dyar feeds on poplar in the 
Eastern States. 
Trichiocampus viminalis (Fallen), an introduced species, oc- 
curs across southern Canada and the Northern States. Its hosts 
are various species of poplar and willow. Full-grown larvae are 
orange-yellow, sparsely clothed with yellow hairs, and about 18 
mm. long. Each side of the body is marked with two rows of 
more or less rounded black spots. Those of the lowest row are 
smaller (fig. 191). 
Winter is spent in the prepupal stage in cocoons in the duff 
beneath the trees. Pupation occurs in the spring and the adults 
appear in May. Young larvae feed side by side on the leaves. 
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