INSECTS ON THE FARM 



301 



387. Structure and feeding of insects. An insect has three 

 distinct regions of the body head, thorax, abdomen ; three 

 pairs of legs, one pair of antennae, and usually one or two pairs 

 of wings. All insects may be divided into two great classes, 

 according to whether their mouth parts are formed for biting or 

 for sucking. If the mouth parts of a grasshopper or cockroach 

 (Fig. 148) are exam- 

 ined, it will be found 

 that there is a distinct 

 pair of jaws adapted 

 for biting and chew- 

 ing. Insects of this 

 class, in feeding, bite 

 off a portion of the 

 solid substance of the 

 leaf or plant and swal- 

 low it. On the other 

 hand, if the head of a 

 squash bug is examined, 

 no jaws will be found 

 (Fig. 149), but instead 

 there is a stout beak 

 fitted for piercing and 

 sucking. As the in- 

 sect feeds, the beak The parts shown are from the mouth of a cockroach 



is thrust down through A > upper lip ; * man ^ r ^ tongue ; A maxillE ; 

 the outer layer of the 



bark or leaf into the soft, succulent tissue beneath, in order 

 to extract the plant juices which nourish the insect. 



Insects with biting mouth parts may be killed by covering 

 the plant on which they are feeding with a stomach poison, 

 such as lead arsenate. Inasmuch as insects with sucking mouth 

 parts do not bite off any of the surface of the plant, they cannot 

 be killed by applying stomach poisons. For these insects, sprays 

 must be used that will kill by their caustic, or corrosive, action 

 on the body of the insect. 



FIG. 148. Parts of an insect's mouth 



