352 REPORT OF THE COMMISSIONERS OF 



other such poison lying on the surface of the plant will not affect these sucking 

 insects and as it is practically impossible to so change the vegetable fluids that an 

 insect will not or can not feed upon them and yet not to damage the plant, we must 

 depend to a great extent on contact insecticides in fighting these pests. The most 

 satisfactory method of killing such insects as aphids or plant lice, scale insects, 

 etc., is spraying them with kerosene emulsion, whale oil soap solution or similar 

 substances. These applications must be made directly to the insects themselves and 

 the effectiveness of the treatment will be proportional to the number of the insects 

 hit. In short, when fighting leaf devouring insects, aim to cover the portions of the 

 plant liable to attack with some arsenical poison, while in controlling sucking forms, 

 it is essential to throw upon the insects themselves a substance which will kill by 

 contact. 



The foregoing are general directions subject to many modifications. Some insects 

 are very resistant to poisons and require large doses before succumbing, but as a 

 rule the trouble is more apt to be lack of thoroughness in. the treatment than weak- 

 ness of the insecticide. Many biting insects like leaf miners, twig, bark and wood 

 borers operate in places where it is impracticable to put the poison. Others feed 

 underground on roots and must be fought in special ways. Sucking insects also 

 present exceptional difficulties. Some are cased with so resistant armor that it 

 is nearly impossible to kill them with substances that will not at the same time 

 injure the plant. The attacks of many plant lice cause the leaves to curl so that 

 it is very difficult to hit them with a spray. Others, like biting forms, may work 

 beneath the surface of the soil, and are therefore nearly inaccessible. Study has 

 shown that in the case of almost every injurious insect there is some point in 

 its life history where it is comparatively easy to keep the pest in check. A little 

 difference in cultural methods will sometimes accomplish much. As a general 

 rule, the wholesale destruction of insect life by the use of deadly sprays is to be 

 avoided. Prevention is the most successful method of anticipating insect depreda- 

 tions. That is, avoid, so far as possible, offering conditions favorable for the 

 development of insects in large numbers. Suppression and control, rather than 

 extermination, should be the aim. The latter is impossible, generally speaking, 

 while the former is frequently our only hope. 



The formulas of some of the insecticides more commonly employed are given 

 here in order to avoid repetition later. Internal poisons like arsenate of lead, paris 

 green, london purple and the like are for use against the insects which devour or 

 eat away portions of a plant and are effective only when the poison can be so placed 

 that the pest must eat it with the plant or go hungry. 



