RELATION BETWEEN MORTALITY OF TREES ATTACKED 
BY THE SPRUCE BUDWORM (CACOE CIA FUMIFERANA 
CLEM.) AND PREVIOUS GROWTH 1 
By F. G. Craighead 2 
Entomologist in Charge of Forest Insect Investigations , Bureau of Entomology f 
United States Department of Agriculture 
INTRODUCTION 
In a recent bulletin 3 reference is 
made to the local variation in mor¬ 
tality following spruce budworm de¬ 
foliation. Several factors are con¬ 
sidered as influencing the percentage 
of mortality, namely: Character of 
defoliation, available soil moisture, 
effects of severe winters, maturity, 
composition of the forest, and vigor of 
the trees. 
But little data bearing directly on this 
last factor had been collected. In an 
earlier paper 4 the following quotation 
occurs: “The dying may be likened to 
•a greatly accelerated natural thinning 
that takes place in a normal forest. 
It is suppressed or overmature trees 
that die first; younger stands suffer 
least.” 
In the first quoted bulletin 5 the 
writer makes the following statement: 
“The vigor of the stand at the time 
of the budworm attack largely deter¬ 
mines the condition in which it will 
come through.” The higher mortality 
in older forests as compared to younger 
forests is very striking, yet often 
spotted and by no means uniform; in 
second-growth stands, which suffer less, 
areas of high mortality are frequently 
found. 
In comparing the rate of growth of 
trees dying on sample plots it was found 
that the slow-growing trees died first 
as well as those receiving heaviest 
defoliation, as illustrated by balsam 
in Table I. 
A more detailed study of this feature 
was contemplated for the summer of 
1922, but time did not permit its fnl- 
Table I. — Radial increment in millimeters for 10-year period before budworm 
attack of trees dying at different periods 
[The first feeding occurred in 1918, the first mortality in 1920. Based on 2-acre plots containing over 350 
trees, Lake Opasatika, Quebec] 
Summer 
1920 
Winter 
1920-21 
Summer 
1921 
Winter 
1921-22 
Summer 
1922 
Winter 
1922-23 
Increment in mm_ ... ... 
8.2 
10. 5 
10.9 
11. 7 
14.0 
15.4 
Percentage of defoliation °__ 
77 
81 
70 
62 
57 
46 
Average diameter, in inches... __ 
5.9 
4.8 
5.7 
6.7 
6.9 
6.1 
<* Percentage of defoliation refers to old needles only at the end of the outbreak in 1921, or earlier in case 
of death. The new growth was completely destroyed each year from 1918 to 1921, inclusive. 
1 Received for publication April 22, 1924; issued June, 1925. 
2 This study was conducted by the writer as part of the 1923 program of work of the Division of Forest 
Insects, Dominion Entomological Branch, Ottawa, Canada. 
The undertaking was greatly facilitated through the interested assistance'of R. E. Balch and H. J. 
MacAloney, graduate students from Guelph College, Ontario, and the New York State College of For¬ 
estry, respectively. The collection of the data for Tables IV to IX and parts of Tables XII and XIII was 
made by the writer in person. On the remainder of the plots both the selection and tabulation were left 
entirely to the discretion of Balch and MacAloney. The compilation of the data was made by all three 
members of the crew. J. D. Tothill also assisted in taking some plots. 
W. G. Wright, in charge of research work for the Dominion forestry branch, Ottawa, kindly assisted 
with suggestions concerning the tabulation of the data. E. N. Munns, Raphael Zon, and S. T. Dana 
offered valuable assistance through constructive suggestions on the preliminary manuscript. 
This presentation represents a considerable condensation of the original manuscript, copies of which, 
with complete tables and data, are filed at the Bureau of Entomology and Forest Service, Washington, 
D. C., the .Entomological Branch, Ottawa, and the New England Forest Service Experiment Station, 
Amherst, Mass. 
3 Swaine, J. M., and Craighead, F. C. studies on the spruce budworm. Canada Dept. Agr. 
Bui. (n. s.) 37, 92 p., illus. 1924. 
4 Craighead, F. C. budworm infestation vs. pulpwood production. 2. Amer. Paper and Pulp 
Assoc., Woodlands Sect. Ser. Proc., Ann. Meeting 2: 8-10, 1922. 
5 Footnote 3, Part II of this bulletin. 
Journal of Agricultural Research, 
Washington, D. C. 
( 541 ) 
Vol. XXX, No. 6 
Mar. 15, 1925 
Key No. K-136 
