Beneficial Insects 

 CHAPTER IV 



BENEFICIAL INSECTS 



So much is written about the injurious insects in bulletins and farm 

 papers that we are apt to look upon all insects as the arch-enemies of 

 mankind. However, if we study those about us carefully we are soon 

 astonished at the number of friends we have among them, friends whose 

 whole existence is one constant warfare against our enemies. It is not 

 enough that we learn to recognize enemies alone; we should know our 

 friends as well and do all we can to encourage and protect them. 



In the preceding pages frequent mention has been made of beneficial 

 insects in connection with the particular injurious species which they 

 help to control. However, out of justice to our insect friends and our- 

 selves it is only right that we devote a few pages to a general discussion 

 of this large but little appreciated group. 



Every order of insects contains forms which feed upon other forms 

 of insect life. However, these friendly species are in some cases so 

 minute that they are overlooked, or their work of ridding our fields of 

 noxious insects is carried on so quietly that their presence is not apparent. 

 Still others so resemble some of the injurious species that their real mis- 

 sion is not suspected. Instead they are blamed for the damage they are 

 really helping to prevent. Many times friends are taken for foes because 

 in searching for the real culprits they are forced to frequent the damaged 

 crop. Unless we are familiar with these insects they often share the fate 

 of the spy who, in order to hide his identity more completely, appears in 

 the role of an enemy. 



Beneficial insects are spoken of as either predacious or parasitic. 

 Owing to the fact that, in habits, these two groups are not clearly denned, 

 but merge one into the other, it is very difficult to give a definition of 

 the terms predacious and parasitic which is wholly satisfactory. 



In a general way insects which wander about in search of the insects 

 upon which they feed are spoken of as being predacious. Insects of this 

 class require many hosts or victims for their maintenance. 



Insects which pass the entire larval stage within the body of a single 

 host, or attached to a single host from which they draw their nourish- 

 ment, are said to be parasitic. 



Parasites gain entrance to the host in many ways. The adult para- 

 site of some species stings its eggs into the body of the host, using for this 

 purpose a sharp organ called the ovipositor. This is usually located at 

 the tip of the abdomen or near it on the underside of the body. Other 

 parasites fasten their eggs onto the surface of the host's body. When 

 the young parasite emerges from the egg it burrows into the host. In 

 other cases the young parasite remains on the outside with only a small 

 portion of its body, including the head, buried in the host. 



The larvae of certain flies are deposited upon the host and immedi- 

 ately proceed to enter its body through natural openings or by burrowing 

 through some tender tissue. 



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