In the spring, after several days of warm weather, but before 
balsam fir buds expand, the overwintering larvae emerge and 
start to feed. The new buds of staminate flowers are attacked first 
if present; otherwise, the larvae bore into old needles. After a 
short period of feeding here, the larvae move to the ends of 
branches and bore into expanding, vegetative buds. Later, they 
feed on the new foliage of developing shoots. When about half- 
grown, they begin tying the tips of two or more twigs together 
with silk, forming a small nest. During this period, old needles 
are avoided until all of the new ones are eaten or cut through. 
Feeding is usually completed during late June or early July. 
Pupation usually takes place within the last-formed nest but 
some occurs at twig axils. Adults appear in about 10 days and are 
subject to considerable dispersal by the wind. The female does not 
fly until she has deposited one or two egg masses. Wind dispersal 
may be the most important factor influencing population trends 
in any given area (5432). 
In light or moderate infestations, spruce budworm injury is 
restricted to the partial loss of new foliage, especially in the 
upper portion of the crown. Damaged needles on webbed branch 
tips turn reddish-brown by mid-summer. In heavy, persistent in- 
festations, all of the new foliage may be consumed (fig. 151) for 
several successive years, and opening vegetative buds and de- 
veloping shoots may be killed in their formative stages. Top 
killing usually occurs after about 3 years of severe infestation, 
F-492901 
FIGURE 151.—Balsam fir defoliated 
by the spruce budworm, Choris- 
toneura fumiferana. 
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