158 t Elementary Principles of Agriculture 



may live on through a longer period, laying eggs con- 

 tinuously, as in the case of the cotton boll-weevil. 



228. The Food of Insects. Insects are very peculiar 

 about the food they eat. Just like the many species of 

 parasitic fungi, each species feeds, usually, on just one 

 kind of plant or animal, or on closely related plants or 

 animals. In such cases we speak of the plant as the 

 "host" for a particular insect. The Colorado potato 



Fig. 96. Colorado potato beetle, a, eggs; b, larvse; c, mature beetle. 

 After Riley. 



beetle (Fig. 96) is a native of the West, living on the 

 western species of nightshades. 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. Some- 

 times there is a wide difference in the kinship of the host- 

 plants. The feeding habits of the "boll-worm" of cotton, 

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

 (Figs. 97 and 103), is a striking example of a 'form which 

 feeds on a number of different kinds of plants. When 



