HOW TO COMBAT THE ATTACK OF INJURIOUS FOREST INSECTS. 5 
II. How to Combat the Attack of Injurious Forest Insects. By 
Wituram SomervIL_e of Cormiston, D.(ic., B.Sc., F.R.S.E., 
Lecturer on Forestry, Edinburgh University.* 
The question which naturally suggests itself to our minds 
when we proceed to consider this subject is, “‘ Are our woods really 
attacked by insects in such numbers as to warrant our going to 
the trouble and expense of adopting special measures to meet their 
attack?” or, in other words, “Would the net gain to be derived 
from eradicating or materially reducing the numbers of our forest 
insects outweigh the loss which their presence in our woods in- 
volves?” Now, this question may be answered in one way or 
another, according to the peculiar circumstances of each case. 
Whether we would be justified in resting content with simply 
adopting precautions designed to prevent the undue increase of 
insects, depends upon the amount of success which has previously 
attended such measures, and upon the danger which former experi- 
ence and analogous cases would lead us to apprehend. Whether 
or not we would be repaid for going a step further, and waging a 
war of extermination against the insects which are already on our 
trees, depends upon the amount of damage which they are causing, 
and, in the event of their not being reduced in numbers, on the 
probabilities of their increasing to such an extent as to destroy a 
great deal more. In every case, too, we must take into considera- 
tion the nature of the preventive or remedial measures which can 
be applied, that is to say, whether they are cheap and easy of 
application, and effectual in operation. 
As to the question of damage, I am sure that all careful 
observers who have spent much time in our woods must have come 
to the conclusion that our forest trees sustain an amount of damage 
each year through the attack of insects, which not only justifies 
but imperatively demands our taking some steps to prevent the 
recurrence of such damage in future. In making this statement, 
let me assure you I am not indulging in the amusement of con- 
juring up a phantom in order to show you how expertly I can 
cause it to vanish, neither am I alluding to anything so indefinite 
and undemonstrable that I would experience any difficulty in 
1 Paper read before the Royal Scottish Arboricultural Society at Dingwall, 
August 1890. 
