INSECTS INJURIOUS TO CITRUS FRUITS 615 



breed and increase with great rapidity so that a few individuals 

 escaping the first treatment may in a few weeks make additional 

 treatments necessary, even with the most efficient spraying. 



Spray materials most widely used are the oil emulsions and 

 miscible oils. In Florida there are two kinds of emulsions used, 

 called the boiled emulsion and the cold-stirred emulsion. Direc- 

 tions for making these are given by Mr. W. W. Yothers in Farmers' 

 Bulletin 933, U. S. Department of Agriculture, and are quoted 

 here as the best available: 



''Experiments covering a 10-year period have shown that the 

 best insecticides for controlling white flies and scale insects are 

 those having a base of cheap lubricating oil or what may be called 

 'paraffin oil.' These oils are made into emulsions according to 

 the formulas following. 



"Fish-oil soap at the rate of from 5 to 8 pounds to 50 gallons 

 of water in May, or from 12 to 16 pounds to 50 gallons of water 

 during the winter season, is an effective spray that has been used 

 for many years without injury to the foliage or fruit. 



' 'While both the fish-oil soap and the oil emulsions^are effective 

 in killing the whiteflies and scale insects, experience indicates 

 that the latter are far superior to the former under Florida con- 

 ditions. This superiority is due to the physical properties of the 

 oils. The high boiling point and great viscosity possessed by 

 these oils make them operative over a longer period of tune after 

 application, and, too, they are only slowly affected by average 

 temperatures and showers. Foliage sprayed with miscible oils 

 remains slightly oily in appearance and to the touch for several 

 weeks after apraying. Fish-oil soap leaves no such evidence 

 that the trees have been sprayed. The oil spray is much less 

 affected by showers than is the fish-oil-soap spray. Summer 

 showers falling after the oil spray has once had an opportunity 

 to dry on the foliage have little effect in lessening the efficiency 

 of the spray. Such showers, however, have a very evident effect 

 upon the number of insects killed by the soap spray. The effective- 

 ness of the weaker strengths of fish-oil soap is much more reduced 

 by showers than is the effectiveness of the weaker strengths of 

 oil sprays. 



''In experimental work on a large scale for the control of the 

 citrus white fly the miscible-oil sprays have given better results 



