616 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



than have the soap sprays. This greater efficiency seems to be 

 due, not to a higher percentages of larvae and pupae killed when 

 the spray is applied, but to the effect that oil sprays exert upon 

 unhatched eggs or upon the young larvae hatching from them 

 within 10 to 14 days after spraying. The oil forms a film over the 

 eggs which prevents a large percentage from hatching, and the 

 young larvae from those which do hatch are killed either in the 

 act of emerging from the shell or in crawling over the oil-coated 

 leaf. Those who are in touch with the white-fly problem 

 appreciate the fact that no matter how efficacious an insecticide 

 may be in killing larvae and pupae on the leaves at the time 

 the spray is applied, if it does not either kill these unhatched 

 eggs or remain operative long enough to kill the larvae that sub- 

 sequently hatch, much of the benefit of spraying is counter- 

 balanced by reinfestation. 



'' There are two ways of making miscible-oil emulsions: 

 (1) Without heat; (2) with heat. The first is called the 'cold- 

 stirred emulsion' the second, the 'boiled' emulsion. Both 

 kinds of emulsion are efficient, reliable, and easily made. 



Cold-Stirred Emulsion. 



,-v , ., FORMULA. 



Fish-oil soap: 



By weight 8 pounds 



By measure 1 gallon 



Paraffin oil, 24 or 28 Baume 2 gallons 



Water 1 gallon 



'' Directions for preparation. In preparing the stock mixture," 

 the soap should be put into a receptacle of about five gallons 

 capacity and the oil added while the mixture is being vigorously 

 stirred. It is important that the oil be added in small quantities 

 at first, and that the stirring be sufficient to keep the oil and soap 

 in the form of an emulsion after each addition of oil. Thus, at 

 first about a pint of oil should be added to the soap and the 

 mixture stirred until no free oil appears. As the amount of oil is 

 increased it should always be stirred or mixed thoroughly before 

 the next -addition is made. After the required amount of oil 



