CHAPTER XV. 

 INSECTICIDES. 



Those insecticides spra3"ed or dusted are generally 

 divisible into two classes: (1) poisons which kill by being 

 eaten; and (2) oils or dusts which kill the insect by pene- 

 trating the skin or by clogging the breathing-pores. 

 Poisons are used for insects such as grasshop23ers, cater- 

 pillars, beetles, etc., which bite jxnd chew their food (see 

 page 12). Contact insecticides are used against insects, 

 such as plant-lice, scale-insects, etc., which suck up the 

 juices of the plant through a slender beak (see page 13) 

 and which are not affected by poisons applied to the sur- 

 face of the plant. 



Gases are used against certain insects which cannot be 

 effectively destroyed by sprays or other uitJttiib. They kill 

 by suffocation (see page 18). 



Bordeavx mixtnre sometimes acts as a preventive against 

 insects by rendering the food-plant distasteful to them.* 



* Bordeau Mixture : 



Copper sulphate (bluestone) 4 pounds 



Fresh lime (unslaked) 6 " 



Water 40 gallons 



Dissolve the bluestone in a half barrel of water by hanging in a 

 bag over night. Slake the lime and add to a half barrel of water. 

 Pour the two half barrels of bluestone solution and lime into a third 



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