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 has 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 with 
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, Wyo., 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, Canada (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, 
Tn this region one or two 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 1 
outbreaks with the hemlock looper and assists in the destruction 
wrought by this insect. 
136650°—38——6 
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