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PRINCIPLES OF FARM PRACTICE 



of how insects interfere so much with farm production, 

 though not so directly as those facts already considered. In 

 general, their rapid growth and reproduction are means for 



equipping them to meet un- 

 favorable conditions. For ex- 

 ample, where a large number 

 of a certain kind of insect is 

 produced, and conditions be- 

 come unfavorable, more of 

 them will survive than if the 

 number produced were small. 

 Rapid growth is. also an ad- 

 vantage. It enables insects 

 to make use of a food supply 

 while it is plentiful, and thus 

 rapidly pass into a stage dur- 

 ing which little or no food is 

 needed. For example, the 

 young of the potato beetle 

 eat much and grow rapidly 

 for a few weeks, then pass 

 into a resting stage, called 

 pupa, in which they require 



Life history of the Hessian Fly. 



a. Egg. b. Larva. 



c. Flax seed or pupa case. 



d. Pupa. e. Adult male. 

 /. Adult female. 



g. Flaxseed on wheat plant. 



h. Fly depositing eggs on blade of 

 wheat plant. 



(Hanman: Missouri Agricultural 

 Experiment Station.) 



no food. 



In temperate climates, the 

 most serious adverse condition 

 which insects must meet is 

 the cold of winter; but they 



meet this difficulty so success- 

 fully that when spring comes there is enough to begin a new 

 season. Insects pass the winter in various ways; some, like 

 grasshoppers, survive in the egg stage; others like the cod- 



