QUESTIONS 



371 



diseases, which at times attack insect pests of agriculture. Figure 



374 represents caterpillars killed by a bacterial disease. Figure 



375 shows a grasshopper which has 

 died on account of a disease. In the 

 former case the dead insects hang 

 limp and for a time after death are 

 filled with fluid, denoting bacterial 

 activity. The body contents of an 

 insect killed by a fungus are com- 

 paratively dry. 



At times one finds thousands of 

 chinch bugs in the autumn killed by 

 a fungus originating in the field. 

 Several attempts were made some 

 years ago to introduce among chinch 

 bugs a fungus prepared in the labora- 

 tory, with the hope that their numbers 

 might be materially reduced thereby. 

 This did not prove practical, since, 

 apart from the difficulties attendant 

 upon its distribution, it required damp FIG. 375. A grasshopper killed by 

 weather in order to grow, and under 



such conditions we find a fungous disease originating naturally 

 in the field attacking the insects in question. 



QUESTIONS 



1. Name four directly beneficial insects, and state why each is useful. 



2. What is a predaceous insect? Name four useful forms in this group. 



3. What is a parasitic insect? Give four examples. 



4. How, in this connection, would you classify burying beetles, flesh-flies 



dung beetles, grasshoppers, and white grubs? 



5. How do bacterial and fungous diseases affect insects? 



