(HAP. XI. | THE CONTROL ( IF INSECT PESTS OF CROPS. 101 



ounces of concentrated size in half a gallon of hoi water and 

 adding one pound oi sofl soap. \\\<> gallons "I kerosine are 

 then warmed carefully in the open air over a small fire — it is 

 scarcely necessary to remark that no attempt must be made to boil 

 kerosine over a fire — or by placing the container in a vessel of 

 boiling water and as much naphthaline is added as will dissolve in 

 the kerosine (about eight pounds as ,1 rule). The two solutions are 

 then mixed together whilst hot. half a gallon of water is added and 

 the whole thoroughly stirred or churned up together. 



Lime-Sulphur, at a strength of 3 gallons of concentrated solution 

 to 100 gallons of spray material, has A \ >t) been found effei ti\ e as a 

 stomach-poison for caterpillars although its action is very slow. 

 Lead Arsenate may be mixed with it if required. Lime-Sulphur, 

 however, is generally used as a Contact Insecticide, especially for 

 Mites. (See page 103.) 



Contact Poisons. 



Contact Poisons, although actually effective against almost all 

 insects, are practically only used in the case ol sucking insects as 

 it is usually more economical to apply a stomach poison in the 

 of insects with biting mouth-parts. The Contact Poisons include 

 various Emulsions and Washes based on the use of Oils, Soaps, 

 Rosin, Sulphur, Lime, Tobacco, Phenyle and various other sub- 

 stances. 



Crude Oil Emulsion is a verj satisfactory insecticide which is 

 largely used in India. It contains 20 pi ij soft (fish-oil) 



soap and 80 per cent, of crude kerosine-oil. When properly 

 made, it forms a homogeneous mixture ami emulsifies well with 

 water, but care should be taken to see that the oil has not separated 

 out from the soap. If a thick black liquid is found floating freely 

 on the surface of the contents of drums or packages, the emulsion 

 should not hi- accepted or used for spraying plants. It is obtain- 

 able ready-made and is usually put up in five-gallon drums which 

 cost about seven rupees in Calcutta. It is used at a strength of 

 about one part by volume to sixty-four ol water (half a pint to a 

 kerosine tin). Care must be taken to see that it is properly strained 

 before placing the mixture in a sprayer. If no strainer is available 

 the emulsion may be placed in a bag or cloth and kneaded by 

 hand until it has passed through and mixed with the water, which 

 should then be churned up by means of the sprayer. Crude oil 

 emulsion may be used against all sucking insects except those 

 which are protected from wetting by hairs or scales; for such a 

 rosin compound must be used. A bag of crude oil emulsion placed 

 in the water-channel when fields are being irrigated will drive 



