39 



but where the adult deposits its eggs inside the tissue be- 

 neath the outer layer, this method is of little value. The 

 application of certain substances like coal tar, tobacco, etc., 

 is sometimes used as a repellant. Methods and contrivances 

 to keep the insect away will be noted under the special in- 

 sect. 



The sucking insects cannot be destroyed by putting poison 

 like Paris green on the plant, since these insects do not eat 

 the outside of the plant and hence not the poison. They 

 can insert their mouth-parts through the surface of a leaf 

 covered with Paris green, for instance, and not eat it, but 

 suck the pure juice from the part beneath. They must be 

 killed by simple contact with some chemicals, and a sub- 

 stance like Paris green, which is very poisonous to insects 

 if it be eaten, may not a£fect the insect in the least to have 

 it covered with the poison. Perhaps the most effectual sub- 

 stance with which to kill sucking insects is what is known 

 as Kerosene Emulsion. (See formula under Insecticides.) 

 This must be thrown on the plant in the form of a spray by 

 means of some kind of a force pump. (See spraying appa- 

 ratus.) Pyrethrum is an active substance in killing by con- 

 tact nearly all kinds of insects, but unfortunately it is of 

 late years so adulterated that it is almost useless for the far- 

 mer. It comes in the form of a powder and can be dusted 

 on the plants by means of a bellows or mixed with water 

 and thrown on in the form of a spray. (See Insecticides.) 



The biting insects can be destroyed by poisoning the parts 

 of the plants effected. To accomplish this we can resort to 

 a large number of chemicals, compounds and patent insecti- 

 cides. Some of the most useful being Paris green, London 

 purple. White Hellebore, etc. A number of the patent in- 

 secticides (so called) that are advertised to kill all kinds of 

 insect enemies are of no value to the practical farmer. 



The mode of applying the different poisons to kill biting 

 insects varies with the kind of plant infested and also with 

 the insect. Some are simply dusted on to the plant as a 

 powder, others sprayed on with a force pump. The methods 



