Insect Enemies and Allies 



195 



metamorphosis there is a complete change, we have four 

 stages : first the egg, then the larva, then the pupa, and 

 after that the adult insect. Where the changes are 

 not so great, as in the grasshopper, we have three stages : 

 the egg, the nymph, and the adult. 



Sprays for killing insects. When we have learned 

 how different insects feed, we can more intelligently 

 set about to destroy them. fc For example, -there are 

 many pests that live on the inner juices of plants by 

 thrusting their beaks through the surface and sucking 

 out the food. It would plainly be labor lost to try to 

 kill these insects by spraying a stomach poison on the 

 leaves. Not being able to poison their food, we must 

 use what is called a " contact poison," that is, some- 

 thing like kerosene, 

 which, coming in con- 

 tact with the outside of 

 the body, will kill the 

 insect (Fig. 149). 



Insects like potato 

 bugs and cutworms, on 

 the other hand, feed 

 directly upon the leaves 

 or other parts of plants, 

 biting off pieces and 

 swallowing them. 

 Spraying arsenical poi- 

 son upon the surface 

 that is attacked is there- 

 fore an effective remedy 

 for biting insects. 



The number 

 of stages 

 of insect 

 life 



Feeding 

 habits of 

 insects 



F. E. Lutz, Am. Mus. Nat. Hist. 

 FIG. 149. Sucking insects. Aphids (plant 

 lice) that cause curl leaf in currants (en- 

 larged). These aphids work on the under 

 surfaces of the leaves. Kerosene emulsion, 

 to reach them, should be applied before the 

 leaves become much curled. The two- 

 spotted ladybird is the great enemy of this 

 pest. 



Sacking 

 and biting 

 insects 



