156 



Elementary Principles of Agriculture 



insect. The Colorado potato beetle (Fig. 96) is a native 

 of the West, living on the western species of night- 

 shades. When the Irish potato was introduced, it found 

 a plant closely akin to its regular food plants, and on 

 which it thrives to such an extent that it takes its 

 name from the new host-plant. Sometimes there is a 

 wide difference in the .kinship of the host-plants. The 

 feeding habits of the "boll-worm" of cotton, or the 



Fig. 96.", Colorado potato beetle. After Riley. a, eggs; 

 b, larvae; c, mature beetle. 



"ear-worm" of corn, the same insect in both cases 

 (Fig. 97), is a striking exception to the general rule, 

 because it feeds on a number of different kinds of plants. 

 When insects do not find acceptable host-plants, they 

 die. Many insects are exclusively flesh-eating, such as 

 the common "doodle-bugs," wasps, lady-bugs, and many 

 species of wood ants. Red bugs and mosquitos are 

 common forms of blood-sucking insects. Many para- 

 sites are solely responsible for the spread of diseases. 



