A, F-485946; B, F-485947; 
C, F-531261; D, F-531899 
Figure 192.—The larch sawfly, Pristiphora erichsonii. A, 
Ovipositing female; B, eggs in new shoot; C, mature 
larvae; D, cocoons. 
Overwintering cocooned sawfly larvae are destroyed in enormous numbers by 
small mammals, especially shrews and voles. High surface water in tamarack bogs 
also destroys large numbers of cocoons at times. A moderate number of species of 
parasites occur but only two, the imported ichneumonid Mesoleius tenthredinis 
Morley and the tachinid Bessa harveyi (Townsend), have been common during the 
current outbreak in central Canada and Minnesota, which began about 1938. 
Initially, M. tenthredinis was quite effective in control; however, the sawfly Gevel- 
oped an immunity to it in central Canada, Minnesota, and Wisconsin (335). 
In 1961, the ichneumonid Olesicampe benefactor Hinz was introduced from 
Europe to Canada; this has added a very promising parasite to the biota for control 
of the larch sawfly. This parasite was first established in the Prairie Provinces, 
transferred eastward in Canada, and then to several locations in the Central and 
Eastern United States (341, 704, 1216). 
403 
