INSECTS IN RELATION TO MAN 399 
with the least possible cost of labor and money; and, third, to 
estimate as exactly as possible the expenses of such prevention, 
or to furnish the data for such an estimate, in order that each 
may determine for himself what is for his interest in every 
case arising. 
“The subject matter of this science is not insects alone, nor 
plants alone, nor farming alone. One may be a most excellent 
entomologist or botanist, or he may have the whole theory and 
practice of agriculture at his tongue’s end, and at his fingers’ 
ends as well, and yet be without knowledge or resources when 
brought face to face with a new practical problem in economic 
entomology. The subject is essentially that of the relations 
of these things to each other; of insect to plant and of plant 
to insect, and of both these to the purposes and operations of 
the farm, and it involves some knowledge of all of them. 
“As far as the entomological part of the subject is con- 
cerned, the chief requisites are a familiar acquaintance with 
the common injurious insects, and especially a thorough 
knowledge of their life histories, together with a practical 
familiarity with methods of entomological study and research. 
The life histories of insects lie at the foundation of the whole 
subject of economic entomology; and constitute, in fact, the 
principal part of the science; for until these are clearly and 
completely made out for any given injurious species, we can- 
not possibly tell when, where or how to strike it at its weakest 
point. 
“ But besides this, we must also know the conditions favor- 
able and unfavorable to it; the enemies which prey upon it, 
whether bird or insect or plant parasite; the diseases to which 
it is subject, and the effects of the various changes of weather 
and season. We should make, in fact, a thorough study of 
it in relation to the whole system of things by which it is 
affected. Without this we shall often be exposed to needless 
alarm and expense, perhaps, in fighting by artificial remedies, 
an insect already in process of rapid extinction by natural 
causes; perhaps giving up in despair just at the time when the 
