THE SPRUCE BUD WORM /) 



Injury to jack pine in the Lake States appears to be most severe 

 in overmature or open-grown stands. Such t rees produce an abundance 



of >t animate flowers, which serve as food for young larvae before new 

 foliage appears. 



Where heavy outbreaks occur in the spruce-fir region, some trees die 

 the fir>t year after severe defoliation, mortality increases the second 

 and third years, and some trees will die 5 or more year- after the out- 

 break has subsided. Secondary insects and fungi may be instrumen- 

 tal in killing the weakened trees. 



Description of Its Life Stages 



The egg. larva, pupa, and adult, as well as the characteristic feeding, 

 of the spruce-fir form of the budworm are shown in the colored illus- 

 tration on the cover. The moth has a wing expanse of seven-eighths 

 inch and in general is grayish with brown markings. The eggs, which 

 are laid on the foliage, are pale green. The egg masses each contain 

 from 10 to 50 or more eggs, which overlap one another like the scales 

 of a fish. The hibernating first-stage larva, or caterpillar, is yellowish 

 green when it first emerges in the spring. The head is blackish brown. 

 The feeding larva becomes brown, and when full-grown it is dark 

 reddish brown and nearly 1 inch in length. The head is dark brown 

 or shining black. The pupa is about five-eighths inch long, pale 

 brownish yellow when first formed, and later changes to dark reddish 

 brown. 



Its Seasonal History 



In the Northeastern States the moths emerge and deposit their eggs 

 late in June and early in July and in the Lake States late in July. 

 The eggs hatch in 8 to 12 days, and the young larvae crawl about. 

 apparently without feeding, until they find a suitable place, under 

 bark scales on the twigs or tree trunks, to spin their silken cases, or 

 hibernacula. The larvae become active in the spring at about the time 

 the buds of balsam fir and red spruce are swelling, which is late in 

 April or early in May in the Northeastern States. They first tunnel 

 the old needles and then enter the opening buds, where they feed on 

 the new needles. As the new growth elongates, the larvae tie the tips 

 of the twigs together to form small nests, in which they feed. The 

 larvae become full-grown in June and pupate on the trees. The pupal 

 period lasts only a few days and the moths emerge and lay their eggs 

 a week or 10 days later. 



Natural Agencies That Check Its Multiplication Between 



Outbreaks 



Inasmuch as the spruce budworm population remains at a low level 

 for long periods between outbreak-, it is certain that such factors as 

 adverse weather conditions, diseases, predators, and a large number of 

 species of parasites play an important part in the natural control. 

 When conditions for increase become favorable, however, epidemics 

 break out and natural enemies arc unable to control the insect. 



