February, ’23] graham & ruggles: economic entomology and forestry 59 
proved the solution of several problems which appeared at one time to 
be impossible of solution. 
About the first work of this sort to be published was that of Craighead 
on the locust borer. Previous to the publication of his bulletin almost 
every state in the range of the black locust as well as the federal depart¬ 
ment had its publication, dealing with this insect. Not one of these 
many publications could suggest any practical means of reducing the 
losses in forest plantings of this tree. Craighead put two and two to¬ 
gether and. found a simple and practical remedy which adds very little 
to the cost of growing locust posts. He found that by planting in such 
a way as to shade the trunks of the growing trees either by shadows 
cast by the trees themselves or by other trees that the injury due to the lo¬ 
cust borer is reduced to a minimum. This same principle applies to a num¬ 
ber of injurious borers such as the bronze birch borer, and the two lined 
chestnut borer, neither of which will attack trees growing in a close 
stand. 
Another insect that can easily be controlled by a silvicultural method 
is the white pine weevil. Several years ago one of us determined that 
in fully stocked stands of white pine the injury caused by this insect was 
a negligible matter. At that time the recommendation was made to 
plant 6' x 6' in Minnesota and 5' x 5' in the east. If openings caused 
by the dying out of trees are kept filled by replacement plantings we 
can be certain of a final crop of straight merchantable trees. Recently 
Peirson, working independently of any knowledge of this previous work 
has come to essentially the same conclusions. 
In the budworm infested area the balsam is not injured to the same 
degree in all stands. In the same locality and under similar con¬ 
ditions of soil, elevation, and exposure we frequently find some stands 
with 100 percent dead balsam and others with less than 50 percent dead. 
It is evident that in the area where less than 50 percent was killed that 
some factor or factors had a decided effect in checking the budworm. 
It seems quite probable that such stands would never have suffered at 
all from budworm injury had it not been for the excessively heavy 
infestation in surrounding stands. From the comparison of sample 
plots in the infested region it appears that the seriousness of budworm 
injury is related to the composition of the forest. Generally speaking 
the mixed stand of balsam fir, spruce, and hardwoods is much less sus¬ 
ceptible to injury than is the pure or nearly pure stand. The injury is 
directly proportional to the percentage of balsam fir in the stand. This 
