298 AGRICULTURE. 



(2) Do you find eyes, spiracles, and mouth-parts? 

 How do they compare with those of the adult moth ? 

 (See mouth-parts of the butterfly.) 



(3) Make drawings of the entire larva, showing all 

 parts. 



(4) Remove the mouth-parts, and draw. Are they 

 adapted for biting or sucking? 



VI. Economic Classification of Insects. 



Insects are divided into two great groups ac- 

 cording to their mouth-parts, in order that one 

 may know what insecticides to apply in com- 

 bating them 



Group I. This includes all insects in that 

 stage of their development in which their mouth 

 parts are formed for biting. These insects 

 actually bite off, chew, and swallow small por- 

 tions of the plant or other material upon which 

 they feed. Consequently, they would be killed 

 by poison placed upon the food and taken into 

 the stomach. Common examples of this group 

 are grasshoppers, beetles, and caterpillars. 



Group //. This includes all insects in that 

 stage of their development in which their mouth- 

 parts are formed for sucking. These insects 

 obtain their food by thrusting the beak below 

 the surface of the plant or animal upon which 

 they feed and sucking its juices, but they do not 

 swallow any of its tissue; hence, poison placed 

 upon the surface of the plant-food would not be 

 taken into the stomach by the insects of this 



