INSECT ENEMIES OF WESTERN FORESTS 



81 



involved. As the caterpillars feed within the buds, or within clusters 

 of needles, they are difficult to reach with stomach poisons. Out- 

 breaks usually cover thousands of acres of rough, mountainous 

 country, and it is rarely possible to apply poisons with any type 

 of ground machine. Airplane dusting lias been used in eastern 

 Canada with fair success. Along roadways and in parks the bud- 

 worm can be controlled by the application of arsenical sprays Avith 

 the aid of power pumps just after the buds open in the spring. 

 Such control work has recently been done in the Shoshone National 

 Forest, Wvo., with fair results. 



Figure 39. — A forest after defoliation by the spruce budworm. 



The black-headed budworm {Peronea variana Fern.) is an im- 

 portant defoliator in balsam fir, hemlock, and spruce forests in the 

 northern part of the United States, Canacla (3) , and Alaska. In the 

 Northeast and in eastern Canada it has appeared in destructive 

 numbers only where mature balsam fir forms a high percentage of 

 the stand. 



In the Pacific Northwest hemlock appears to be the preferred host, 

 although Douglas fir, balsam fir, spruce, and larch are also attacked. 

 In this region one or tw^o outbreaks have been recorded in which 

 thousands of acres of western hemlock have been severely defoliated. 

 Fortunately, however, this has resulted in killing very little mer- 

 chantable timber. Frequently the black-headed budworm occurs in 

 outbreaks with the hemlock looper and assists in the destruction 

 wrought by this insect. 



130643°— 39-^6 



