LEAFLET 2 42. U. S. DEPT. OF AGRICULTURE 



The Spruce Budworm, Its History and Distribution 



Tlie spruce budworm is a native species and is found throughout 

 practically the entire range of its food plants on this continent. In 

 Maine serious outbreaks occurred about 1807 and again about 1878, 

 The most serious outbreak on record began in Quebec about 1909, ap- 

 peared in Maine in 1910 and in Minnesota in 1913, and continued its 

 ravages for nearly a decade. About 1923 the budworm began to 

 attract attention in the Lake States as a pest of jack pine. Several 

 outbreaks have occurred in the western part of the United States on 

 Douglas fir, alpine fir, white fir, Engelmann spruce, blue spruce, lodge- 

 pole pine, and ponderosa pine. A very extensive outbreak in Colo- 

 rado is now causing considerable damage to all these species except 

 loclgepole pine. 



Its Host Trees 



In the Northeastern States, the Lake States, and eastern Canada, 

 balsam fir is the favored food plant ; in the Lake States and part of On- 

 tario a biological race prefers jack pine and Scotch pine; in Colorado 

 and the Northwestern States Douglas fir and alpine fir are attacked; in 

 Montana a strain has been recorded on loclgepole pine ; and in Colorado 

 another biological race defoliates ponderosa pine. White fir, the sev- 

 eral species of spruce, hemlock, and larch are attacked to a greater or 

 less degree. 



The Nature of Its Injury 



Upon emerging from hibernation in the spring the young larvae 

 tunnel in the old needles and then bore into the opening buds on spruce 

 or fir trees. Later they feed on the developing foliage and when 

 about half -grown they begin tying the tips of two or more twigs to- 

 gether with silk, forming small nests. The new growth is preferred 

 by the growing larvae and is entirely destroyed before the old foliage 

 is eaten. Feeding usually begins at the top of the tree, and when the 

 population is low it is difficult to detect the presence of the insect. 

 In heavy infestations the trees exhibit a scorched appearance, later 

 turning grayish as the foliage disappears, and finally dead tops of 

 dying trees become evident. When the larvae become full-grown 

 they may be jarred from the branches by striking the trunk of the 

 tree several sharp blows with the head of an ax. A cloth mat placed 

 on the ground beneath the trees will facilitate the finding of any larvae 

 which may fall. This method may be employed for determining the 

 relative population density in light to medium infestations to sup- 

 plement estimates of percentage of defoliation. 



Greatest tree mortality occurs in the red spruce-balsam fir type, par- 

 ticularly where fir predominates and is overmature. Little damage 

 has been reported in mixed hardwood-spruce-fir stands, especially if 

 the conifers are overtopped by the hardwoods. White and black spruce 

 appear to suffer less from attack than red spruce and fir, apparently 

 because the opening of the buds and foliage development of the former 

 tree species do not synchronize with larval development as well as in 

 the case of the latter species. 



