4 
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SO MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE 
mature larvae are approximately 1 inch in length, deep brown, with 
yellowish, pale-green markings and numerous small, wartlike erowths 
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 about 12, “and these hatch during the latter part of J uly. 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 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 "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. 
When 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). 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. 
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 destroyed 
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 fohage rather than feed on old needles. 
As in the case of most defohators, 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 usually are responsible for 
eventually subduing an outbreak. 
The control of spruce budworm epidemics by artificial methods 
is not ordinarily practical because of the difficulties and expense 
