two generations per year, and the winter may be spent in the lar- 
val stage (40). 
The larch sawfly, Pristiphora erichsonii (Hartig), probably an 
introduced species, was first recorded in North America at Bos- 
ton, Massachusetts, in 1880. It now occurs in all Canadian Prov- 
inces, in Alaska, and all of the northern tier of States except 
Ohio, Indiana, and Idaho. Its hosts are listed as tamarack and 
Western, European, Japanese, and Siberian larches. In eastern 
America, tamarack is most seriously infested. Full-grown larvae 
(fig. 188), are whitish beneath and gray-green along the dorsum, 
have jet black heads, and are about 16 mm. long. Female adults 
are black and from 6 to 9 mm. long. The abdomen has a broad 
orange band, tapers sharply posteriorly, and is keeled longitudi- 
nally along the midventral line. 
In the Lake States, winter is spent in the prepupal stage in 
the ground. Pupation occurs in the spring and the adults appear 
from mid-May to August, depending on temperature and loca- 
tion. Eggs are laid in rows under the bark of current terminal, 
lateral twigs. Hatching occurs in about 8 days, and the larvae 
move back to the foliage on older twigs, where they usually feed 
in groups. Feeding is completed in about 20 days and the mature 
larvae drop to the ground, enter the duff, and spin tough, papery, 
brown cocoons. Because of the long period of adult emergence, 
feeding larvae, cocooned larvae, pupae, and adults all may be 
found at the same time in early summer. Normally, there is one 
generation per year. Occasionally, however, small numbers of 
second-generation adults are produced. A small number of larvae 
enter dianause and require 2 years to complete one generation 
(210, 307). 
Larch sawfly larvae eat the needles on older twigs, and where 
the attack is heavy, the entire tree may be defoliated. These trees 
do not die readily from defoliation, however, because of their 
ability to refoliate within the same season. Normally, during out- 
breaks the affected trees are characterized by thin foliage, re- 
duced radial and terminal increment, reduced production of nor- 
mal shoots with a tendency toward adventitious growth, and 
branch mortality. Marked loss of radial increment occurs after 
4 to 6 years of outbreak, and after 6 to 9 years of moderate to 
heavy defoliation, tree mortality occurs. Many widespread out- 
breaks have been recorded since 1880 and losses have been severe. 
Since the middle fifties, an estimated volume loss of 40 percent 
in valuable sawtimber and pulp stands has occurred in managed 
forests in Minnesota. Between 1910 and 1926 in Minensota an 
estimated one billion board feet was killed. 
Overwintering cocooned sawfly larvae are destroyed in enor- 
mous numbers by small mammals, especially shrews and voles. 
High surface water in tamarack bogs also destroys large numbers 
at times. Many species of parasites occur but only two, the im- 
ported ichneumon, Mesoleius tenthredinis Morley, and the tachi- 
nid, Bessa harveyi (Townsend), have been prevalent during the 
current outbreak which began in about 1938. Initially, M. tenth- 
redinis was quite effective in control; however, the sawfly de- 
veloped an immunity to it in central Canada, Minnesota, and 
Wisconsin (208). 
458 
