CONTACT INSECTICIDES. 163 



Spraying with Contact Insecticides. 



When it was seen that spraying the foliage with Paris 

 green had little effect on the larger gypsy-moth caterpillars, 

 experiments were made with insecticides which were intended 

 to kill by contact. This was done to find a means of dispos- 

 ing of the masses of caterpillars which did not seem to be 

 much affected by the use of Paris green and which clustered 

 on many trees where fire could not be used. Contact in- 

 secticides, when of a strength sufficient to kill the gypsy- 

 moth caterpillars, are likely to cause injury when used on the 

 foliage. Therefore they can only be used to advantage as a 

 last resort where the caterpillars have stripped trees or 

 where they are clustered in such numbers on the trunks 

 as to make it less expensive to spray with an insecticide 

 than to kill them by hand. 



Kerosene emulsion was first tried. A strong emulsion 

 gave fairly good results but its preparation in the field was 

 not economical. The only way in which it could be made to 

 give satisfactory results was to mix it at a central point and 

 distribute it to the different towns. When it was made in 

 the field the men did not get uniform results. 



Fish oil and whale oil soap gave better satisfaction when 

 used as follows : — 



Take one pound of whale oil soap and slice into thin, 

 small pieces. Place the pieces of soap in a pail and add 

 about a gallon of boiling or nearly boiling water ; then stir 

 until the soap is dissolved ; dilute at the rate of one pound 

 of soap to twenty gallons of water. This formula was pre- 

 pared by Mr. E. P. Felt. 



Solutions made from soap powders also proved efi'ective. 

 The following formula was prepared by Supt. F. H. Jones : — 



Place one pound of "Gold Dust" in a pail; add one 

 gallon of lukewarm (not hot) water; stir briskly until the 

 powder is dissolved ; then add three gallons of cold water ; 

 stir well. 



Where the larvas and pupoe are clustered together on the 

 trunks of trees and in stone walls or other sheltered places, 

 they should be well drenched with the solution. The hand 

 tank (Fig. 1, page 120) and Gem nozzle were found useful 



