ENEMIES OF PLANTS. 299 



group. Plant-lice, scale insects, mosquitoes, Hies, 

 etc., are examples of Group II. 



The student should have already observed 

 that an insect, according to the form of its 

 mouth-parts, may in one stage of its develop- 

 ment belong to one of these groups, while in 

 another stage it belongs to the other as, the 

 tomato-worm, the larval stage of the sphinx- 

 moth, which belongs to Group I., while the 

 adult stage, the moth, belongs to Group II. 



VII. Preventives. 



A small amount of time and labor spent in 

 preventing insects from becoming established 

 on the farm is often of more value than a great 

 amount spent in trying to destroy them. 



1. Removal of Debris. By the prompt re- 

 moval and burning of all dying or diseased 

 branches, trees, or plants, decayed fruits, and 

 general debris, many insects, as well as their 

 eggs, will be destroyed; while if such mate- 

 rial is allowed to remain, it will afford protection 

 for insects during their hibernating and breed- 

 ing seasons, thus promoting the development of 

 overwhelming numbers. 



2. Change of Crops. If an insect pest makes 

 its appearance in a field of grain, one may pre- 

 vent its devastation the following year by plant- 

 ing the field in some other crop upon which the 

 insect does not feed. F^or example, the Hes- 

 sian fly may be observed in a field of wheat. 



