THE PARASITE ELEMENT OF NATURAL CONTROL OF 
INJURIOUS INSECTS AND ITS CONTROL BY MAN 
By L. O. Howarp, Chief Bureau of Entomology, United States Department of 
Agriculture 
When the economic entomologist confronts an emergency problem 
it is his duty to bring measurable relief as speedily as possible. At 
the same time he must begin studies looking forward to natural and 
therefore comparatively costless control. No one at all broadly 
familiar with the insect complex can doubt the importance of the 
insect enemies of insects. So important does their work appear to 
me that I am inclined to rank it the main factor in the preservation 
of the so-called “balance of nature.” Surely it is one which 
demands our most careful attention. 
The food necessities of the rapidly growing human population of 
the world make it necessary for us to grow enormous and increas- 
ing food crops. As we do this, we make equally enormous and 
increasing opportunities for the multiplication of certain insects. 
And does it not occur to you that this in turn should give the insect 
enemies of those certain insects such unprecedented food supples 
that they should increase beyond all previous experience and become 
of the very greatest help to us in the fight to avoid starvation ? 
All this seems logical, and in the long run it will happen in just 
that way. But we want to hasten the process. In the case of crop 
enemies brought in from another part of the world we can not wait 
for the relatively slow adaptation of native parasites to the new host. 
We must bring to the new country the parasitic forms already accus- 
tomed to and adapted (in the course of centuries) to the crop pest 
accidentally imported. 
This is the theory on which so much work has already been done, 
and it is safe to say that, failing some startling discovery which is 
likely to be made at any time, such work is still in its infancy. We 
have seen some strikingly successful results, and some workers have 
been overencouraged. Many instances will occur to you in which, 
carried away by the wonderful success of certain introductions into 
California and Hawaii in the closing years of the last century, highly 
intelligent men, like the late Elwood Cooper, of California, for 
example, have made claims which to-day seem preposterous and 
which even then were discounted by the trained entomologists. 
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