go MISC. PUBLICATION 278, U. S. DEPT. OF AGRICULTURE 



mature larvae are approximately 1 inch in length, deep brown, with 

 yellowish, pale-green markings and nmnerous 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 tipper branches of fir and spruce trees, where the tops are 

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

 of about 12, and these hatch during the latter part of July. After 

 hatching, the young larvae wander about for a few days in search 

 of a suitable place to spin their cocoons and in these they hibernate. 

 It is not definitely known whether the young larvae feed before 

 hibernation, but if they do, it is very sparingly. The following 

 spring they emerge from their winter nests simultaneously with 

 the opening of the new buds, which they immediately attack, enter- 

 ing them either directly through the base or between the opening 

 scales, and hollowing them out. As the new tender needle growth 

 develops this is fed upon. Later on the larvae bind together the 

 needles at the tips of the branches loosel}" Avith silk, bite them off 

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

 frass. ^Vhen disturbed, the larvae hide in these retreats, or drop 

 from the limbs and hang by silken threads, which are used to 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 con- 

 struct loose cocoons of silk and dead needles, in which they pupate. 

 The moths emerge in from 10 to 12 days. Thus there is one gen- 

 eration annually. 



^Mien attacks are heavy entire trees are stripped of foliage and 

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

 ance (fig. 39). AYhen 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. 



In the western part of the United States the balsam firs and 

 Douglas fir appear to be preferred hosts of the spruce budworm, 

 and the greatest damage has occurred in pure stands of these two 

 species. The budworm has also been found attacking Engelmann 

 spruce, western larch, western hemlock, western white pine, pon- 

 derosa pine, and lodgepole pine. Budworm attacks on pines are 

 usually limited to individual trees occurring in association with 

 the preferred hosts, though serious outbreaks in pure lodgepole pine 

 have occurred in and adjacent to the southwestern corner of Yel- 

 lowstone National Park. In all cases the new foliage is destroj^ed 

 first, old needles being attacked only when the preferred supply is 

 exhausted. Larvae will often migrate from one tree to another in 

 search of new foliage rather than feed on old needles. 



As in the case of most defoliators, the spruce budworm is preyed 

 upon by numerous insect parasites and predators and by disease, 

 and these in normal years tend to keep the pest under control. The 

 natural enemies and a shortage of food usualh^ are responsible for 

 eventually subduing an outbreak. 



The control of spruce budworm epidemics b}^ artificial methods 

 is not ordinarily practical because of the difficulties and expense 



