VALUE OF A KNOWLEDGE OF ENTOMOLOGY 3 



which they attain their greatest development is also desirable. 

 To this we must add a knowledge of the ehects of different 

 farm practices upon the insects, as well as of insecticides. 

 There are many insects with which we cannot cope by the use 

 of poisons, and it is only by a thorough knowledge of their life 

 economy from the time the eggs are deposited until the perfect 

 insect emerges, that we are able to mitigate losses from their 

 ravages. The knowledge of some one or more facts appar- 

 ently trivial in themselves may frequently enable us to pre- 

 vent by farming methods injury which we cannot cure by 

 means of poisons, mechanical or other direct methods 



After seed has been selected with reference to its adapta- 

 bility to the soil and climatic and other conditions one of the 

 next problems that confront the grower is how to protect the 

 crop from noxious insects and diseases. Fortunately we know 

 approximately the life history and habits of a large proportion 

 of the injurious insect inhabitants of this country, with the 

 exception of some few species which have only been recently 

 associated with injury, or which have lately been introduced 

 from abroad. 



As a necessary preliminary to the discussion of the insect 

 enemies of the various vegetable crops, some idea of the struc- 

 ture and classification of insects must be given. It is perti- 

 nent to follow as a matter of course with general methods of 

 control, which include (i) mechanical methods, (2) farm prac- 

 tice as preventives and (3) the preparation and means of 

 applying poisons for the destruction of insects. Following 

 this the different groups of insects which affect various crops 

 and are not attached to single crops will be considered. 



CLASSIFICATION OF INSECTS 



If we would have an intelligent understanding of the causes 

 that have led to the destruction of our crops, we must know 

 something of the classification of insects and their nearest rel- 



