220 



AGRICULTURE 



harmless to most plants. Directions for its preparation and use 

 are given in the appendix on page 307. 



Of course external poisons are useless against chewing insects 

 which live in fruits, such as the cotton boll weevil and cur cu'li o. 

 Cultural and other methods must be used against these. 



Sucking Insects. Poison applied to the leaf surface is harmless 

 to sucking insects also. We attack them in another way. In- 

 sects, as you remember, breathe through spiracles, openings in 

 their abdomens. If these spiracles are closed, they perish for 

 lack of air. Applications, such as pry'eth rum powder or tobacco 



APPLES GROWN ON Two BRANCHES 



On the left, apples from a branch sprayed for codling moth ; on the right, apples from an 

 unsprayed branch. This shows comparative quantity and quality of crops from the two 

 branches. 



dust, choke the breathing tubes. Sometimes sucking insects are 

 killed by an application, such as lime, which destroys their body 

 tissues. 



Spraying. Here is good advice about spraying: " Know the 

 enemy to be destroyed; know the remedies that are most effective, 

 and apply them at the proper season. Be prompt, thorough, and 

 persistent." 



EXERCISE 



i. Compare a grasshopper, a moth or butterfly, a bug, a beetle, 

 and a fly. In what ways are they like and in what unlike ? 



