222 



PRODUCTIVE FARMING 



The manner in which these insecticides kill is interesting. 

 Insects breathe through pores or openings in the body not 

 through noses or mouths. When any material clogs these 

 breathing pores the result is death. Suitable materials for 

 this purpose are oils and powders. The oils may be mixed 

 with other materials to prevent any damage to the plants on 

 which the insects live. Kerosene emulsion and the miscible 

 oils are so diluted that no damage will result to the trees 

 or other plants. 



Fio. 122. Moulting of a grasshopper: a nymph ready to change; b the skin 

 split along the back and the adult emerging; c continues the process, and at d the 

 insect is drying out. (From Smith's " Insect Friends and Enemies.") 



It must be remembered that these contact insecticides 

 really smother the insects and must necessarily be applied 

 when the insects are present. They should not be applied 

 in advance, as poisons may be, to prevent the attacks of 

 the insects. 



How Insects Grow. The skin or outside coat of insects 

 becomes very hard and will not stretch. When a growing 

 insect has become so large as to entirely fill this coat, a new, 

 soft coat forms underneath and the old one is shed. This 

 process of shedding the coat is called moulting (Fig. 122). 

 The skin is moulted several times during the life of the insect, 

 and each time the insect becomes larger or changes in other 



