generation adults appear in early July or later and lay their eggs 
in needles. Hatching occurs shortly thereafter, and the larvae 
feed for 3 or 4 weeks. At maturity, they drop to the ground and 
spin cocoons in the litter in which they spend the winter. In the 
northern portion of the species range, some remain in diapause 
for several years before pupating (604). 
The European spruce sawfly found conditions favorable for a 
rapid increase in numbers once it gained a foothold in the spruce 
forests of North America. In 1932, serious infestations were 
found over an area of about 2,000 square miles of the Gaspé. Two 
years later evidence of defoliation was also apparent in Quebec, 
New Brunswick, and adjacent areas in the United States. By 
1935, the Gaspé outbreak covered about 6,000 square miles, and 
tree mortality in some areas had reached serious proportions. 
Conditions continued to worsen through 1937, but in 1938 a gen- 
eral reduction in population levels was reported from nearly all 
regions. The downward trend in populations continued and by 
1942, they had declined to medium or light intensity in all but a 
few restricted localities. The collapse of the outbreak was caused 
by an accidentally introduced polyhedral virus disease (26). The 
virus was first observed in Canadian infestations in 19380, but it 
was not until 1988 that numerous diseased larvae became notice- 
able in parts of New Brunswick. Four years later it had brought 
the widespread outbreak under control. Since then populations 
have been fluctuating at very low levels and the sawfly is no 
longer considered an economic pest (561). 
During the thirties and forties, the Canadian Government im- 
ported and liberated approximately 20 species of parasites in 
infested areas (484). Substantial numbers of these parasites 
were also released in the United States. Two species of cocoon 
parasites and five species of larval parasites became established 
(205). 
FAMILY TENTHREDINIDAE 
The family Tenthredinidae is represented by more than 350 
species in the United States and Canada, the majority of which 
occur in eastern America. The larvae are all leaf feeders, leaf 
miners, gall formers, or fruit borers. Many species are important 
pests of forest and shade trees and forest plantations. 
The antennae of the adults have seven to ten segments and 
range in shape from setaceous and filiform to clavate. The meso- 
thorax is without sterno-pleural sutures, the anterior of the 
scutellum is V-shaped, and the posterior margin usually has a 
distinct posttergite. The tibiae are without pre-apical spurs, and 
the apical spurs of the front tibia usually have the longer spur 
cleft at the apex. The larvae range in length from 10 to 37 mm. 
and are usually largest in diameter at the thorax. The body is 
greenish or variously colored, sometimes with distinct markings, 
and is either smooth, glabrous, setiferous, tuberculate, or spinous 
(621, 801). 
Heterarthrus nemoratus (Fall.) (=Phyllotoma nemorata 
[Fall.]), the birch leaf-mining sawfly, an introduced species first 
recorded from North America in 1905, is now widely distributed 
453 
