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 



