364 MANUAL OF VEGETABLE-GARDEN INSECTS 



2. Sucking imects: This term is usually applied to insects 

 which have the mouth-parts modified to form a beak con- 

 taining four bristles united into a slender tube with which 

 they puncture the tissues of the plant and suck out the juices 



(Fig. 230). Plant-lice and 

 other true bugs possess this 

 type of mouth-parts and are 

 controlled by the use of con- 

 tact insecticides. 



3. Lapping insects : In 

 some flies the mouth-parts 

 are developed into a tongue- 

 like organ with which they 

 are able to lap or lick up 

 liquids but which is not fitted 

 for piercing plant tissue (Fig. 

 231). Sweetened arsenical 

 baits have been used success- 

 fully for the control of some 

 insects belonging to this class. 



How insects breathe. 



Insects breathe through a 

 series of openings called 

 spiracles extending along the 

 side of the body. These open- 

 ings connect with tubes called 

 tracheae which, subdividing 

 again and again, extend to all parts of the body. Some 

 contact insecticides, such as soaps, are supposed to clog the 

 spiracles and kill the insect by suffocation ; others, like the 

 oils, are said to penetrate the thin walls of the tracheae and 

 thus reach a vital part ; and it is thought that the fumes of 

 nicotine arising from the spray applied to the insect are 



Fig. 229. — A grasshopper feeding 

 showing the biting type of mouth- 

 parts. 



