HOW INSECTS FEED 255 



There is a narrow channel extending through the entire 

 length of this tongue through which the butterfly sucks 

 ' the liquids that serve it as food. 



With most sucking insects the mouth-parts are strong 

 enough to enable them to pierce the tissues of plants, 

 animals, or other insects, so that their food is obtained 

 entirely from beneath the surface. This is the reason 

 that it is impossible to kill sucking- insects by applying 

 poisons to the plants on which they are feeding. 



Different treatments for biting and for sucking insects. 

 These types of mouth-parts, must be well understood in 

 deciding just what treatment should be given for any 

 insect pest. With the biting leaf -eating insects, any poison 

 spread on the surface of the leaves will be taken into the 

 insect's stomach with its food and cause its death. Paris 

 green is the principal poison that is used in this way. It 

 is generally mixed with water and the poisoned solution 

 sprayed all over the trees or plants on which leaf-eating 

 insects are feeding. Other poisons may be used in the 

 same way. Such a treatment will have no effect upon the 

 sap-sucking insects that take nothing from the surface 

 of the leaves. It has never been found possible to in- 

 troduce any poison into the sap of a plant so as to destroy 

 che sucking insects upon it. The principal thing that 

 can be done to destroy such insects is to apply something 

 which will not injure the plant, but which, coming into 

 contact with the insect's body, will cause its death. There 

 are two kinds of such treatment that can be used. The 

 first kind includes many substances which cause death by 

 covering with soap or with oil the openings through which 



