162 FARM FRIENDS AND FARM FOES 



these fruits, tents are placed over the trees before the gas 

 is generated. 



In California sulphur is used as a remedy for red spiders 

 and certain leaf hoppers. The sulphur vaporizes in the 

 hot sunshine, and the fumes are fatal to the insects. In 

 greenhouses sulphur is also used by painting heating pipes 

 with it so that the fumes will be given off. 



OBSERVATIONS FOR PUPILS 



1. Make a list of the injurious plant-feeding insects that you know 

 which may be killed by internal poisons. 



2. Make a similar list of those that may be killed by tracheal poi- 

 sons. 



3. What insects in your locality must be killed by the use of noxious 

 gases ? 



4. In what ways have you seen insecticides applied? 



5. Read such of these references as your teacher may direct : 



Important Insecticides, Farmers' Bulletin 127. Carbon Bisulphide as an Insec- 

 ticide, Farmers' Bulletin 145. Spraying for Orchard Insects, Yearbook Reprint 

 480. 



