INSECT ENEMIES OF WESTERN FORESTS 



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Figure 54. — The hemlock sawfly (Neodiprion tsugae) : A, Larvae, x IV2; 

 B, pupal cases; C, adults, natural size; D, defoliated western hemlock twig. 



larch stands of northern Idaho and western Montana. This is the 

 first and last record of their appearance, and, although they oc- 

 curred in countless numbers in 1921, it was practically impossible 

 to find a single larva in 1922. This is a marked example of how 

 rapidly an outbreak can disappear. The larvae did their heaviest 

 feeding from mid-July to the last of August, and either devoured 

 the foliage or killed it by chewing on the fleshy portion of the 

 needles anywhere between the tip and base. The larvae leave the 

 trees when they are mature and spin small silken cocoons under 

 the duff, in which they pupate. Small pebbles and grains of sand 

 adhere to these cocoons, giving them the appearance of small 

 lumps of dirt. The winter is passed in the cocoon, and the new 



