INSECT ENEMIES OF WESTERN FORESTS 103 



gion, the Southwest, and the Pacific Northwest from Alaska to 

 California. There are many records of spruce budworm epidemics, 

 in which enormous numbers of spruce and balsams have been 

 destroyed, in the Northeast, in Canada, and in the Lake States. 

 Although it had been found in the West as early as 1915, it was 

 not until 1922, when two outbreaks were recorded in widely sepa- 

 rated sections of Idaho, that it was recognized as an important 

 enemy in western forests. Since then outbreaks of tremendous 

 scope and destructiveness have occurred in the northern Rocky 

 Mountain region, in Colorado, and in the Pacific Northwest. 

 Though it is not known whether the spruce budworm migrated or 

 spread to the western part of the United States from infested 

 areas in the East, it is believed to be indigenous to the West, and 

 during the last 30 or 40 years it has been at such a low endemic 

 stage as to escape attention. 



The adult spruce budworms are small, mottled, buff -colored to 

 grayish moths with a wing expanse of approximately 7 / 8 inch, and 

 with no distinctive markings, the general color tone being a dull 

 gray. The oval, scalelike eggs, which are light green and about 

 y 16 inch in diameter, are laid on the under side of needles, over- 

 lapping like shingles, with about one-third of the egg exposed. The 

 mature larvae are approximately 1 inch long, deep brown, with 

 yellowish, pale-green markings and numerous small, wartlike 

 growths along the sides. 



The moths can be seen hovering around infested trees late in 

 July or early in August. The females lay their eggs on the needles 

 of the upper branches of fir and spruce trees, where the tops are 

 in the sunlight. A female lays approximately 150 eggs in masses 

 of 12 or more, and these hatch in about 10 days. After hatching, 

 the young larvae wander about for a few days in search of a suit- 

 able place to spin their cocoons, in which they hibernate until the 

 following spring. In May they emerge from their winter hiber- 

 nacula and first mine old needles, then attack the opening buds, 

 entering them either directly through the base or between the 

 opening scales, and hollow them out. As the new tender needle 

 growth develops, this is fed upon. Later the larvae bind the needles 

 at the tips of the branches together loosely with silk, bite them 

 off at the base, and form a shelter of dead needles, bud scales, and 

 frass. When disturbed, the larvae hide in these retreats, or wriggle 

 violently, drop, and hang on silken threads, using these threads 

 for their return to the nests if no further disturbance occurs. After 

 3 or 4 weeks of feeding, about the last of July, the larvae reach 

 maturity and construct loose cocoons of silk and dead needles, in 

 which they pupate. The moths emerge within 10 to 12 days. There 

 is one generation annually. 



When attacks are heavy, entire trees are stripped of foliage and 

 killed and large forest areas take on a brownish, scorched appear- 

 ance (fig. 44). When defoliation is not so complete the trees show 

 a blighted or scorched appearance at the tips of limbs where the 

 new foliage has been destroyed. Even moderate feeding tends to 

 reduce growth, weaken the trees, and render them susceptible to 

 later destruction by secondary insect enemies. 



