INSECTS 203 



application of some poisonous material to the plants on which 

 they feed, as when we put poison on potato vines to kill the 

 potato beetles. When biting insects such as bark beetles 

 and tree borers feed in protected places it is impossible to 

 apply the poison, and some other remedy must be found if 

 possible. To decide what remedy to use we must first know 

 the kind of mouth parts and the feeding habits of the insects. 

 Insects with sucking mouth parts usually live upon the 

 sap of plants or the blood of animals; a few of them, such as 

 bees, butterflies, and moths, largely feed upon the nectar of 

 flowers. The stone-fly and a few others get most of their 



Fig. 121. — Bean-weevil, natural size and enlarged, and a much infested bean. 

 (From Smith's "Insect Friends and Enemies.") 



food when in the larva or youngest stage and have no true 

 mouth parts when they come to the adult stage. Such 

 insects live only a short time in the adult stage, their chief 

 purpose being to lay eggs for the next brood; when this is 

 done they soon die. 



The larva form of the butterfly has a biting mouth, while 

 the adult has a sucking mouth. This is also true of flies and 

 mosquitoes. 



As sucking insects get their food from the inside and not 

 outside the objects on which they feed, we cannot poison 

 them. We must resort to more difficult methods of fighting 

 them. 



Contact insecticides are substances which will kill insects 

 by coming into contact with them or by covering their bodies. 



