48 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



recommended cannot possibly bear enough arsenic to be injurious, 

 and that cattle or horses may be pastured under trees sprayed 

 with arscnicals with impunity.* 



2. Contact Insecticides 



Contact insecticides are used against insects with sucking 

 mouth-parts and soft-bodied biting insects, which may be more 

 readily destroyed by this means than by arsenicals. These sub- 

 stances arc fatal to the insect either by clogging the spiracles 

 or trachea, and thus causing suffocation, or by corroding the 

 skin. It should be remembered that the chitinous skin of most 

 insects is not easily corroded, and that in most cases a material 

 strong enough to penetrate the skin will also injure foliage, so that 

 only soft-bodied insects can be combated with corrosive sub- 

 stances upon foliage. 



In the application of contact insecticides it is absolutely essen- 

 tial that the spray come into contact with the insect, as a mere spray- 

 ing of the foliage is of no value whatever. 



1. Kerosene emulsion is one of the oldest remedies for plant- 

 lice, and other sucking and soft-bodied insects, and is often 

 resorted to because it is readily made and the materials are 

 always at hand. 



Dissolve \ pound of hard or whale-oil soap (or 1 quart soft 

 soap) in 1 gallon of boiling water. Add 2 gallons of kerosene and 

 churn with a force pump by pumping back and forth for five to 

 ten minutes until the oil is thoroughly emulsified, forming a 

 creamy mass with no drops of free oil visible. This stock solution 

 is now diluted so that the resulting mixture will contain the de- 

 sired per cent of kerosene. Thus for aphides one part of the stock 

 solution should be diluted with from 10 to 15 parts of water, giving 

 from 4 to 6 per cent of kerosene in the spray, while for a winter 

 wash for San Jose scale, it should be diluted only three or four 



* This is not true of grass beneath trees which have been sprayed with 

 a straight-jet fire-hose, as is commonly done in Massachusetts in the extensive 

 operations against the gypsy moth, but refers to spraying which has been 

 done with an ordinary spray nozzle, which applies the material as a fine spray. 



