458 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 10 



It cannot be stated whether the oil spray killed a larger percentage 

 of the eggs than the soap spray as the eggs themselves were not exam- 

 ined at the time of spraying, and the newly hatched larvae which would 

 naturally feel most the hold-over effect of the spray are quite apt to 

 fall from the leaf if they succumb before they have settled to feed. 

 As the spraying was done by the writers themselves with the aid of a 

 power outfit, on the same days and after much experience in manipula- 

 ting a spraying outfit, it is unlikely that the oil and soap sprays were 

 apphed with such differences of thoroughness as to account for the 

 marked differences in effectiveness recorded in Table II. As each 

 strength of insecticide used in the work of Table II is known to be 

 effective from a kilhng standpoint if brought in contact with each 

 insect and permitted to act unmolested by rains, with the exception of 

 the weakest strength of fish oil soap when used against mature larvse 

 and pupae, the writers are of the opinion that the differences in the 

 general effectiveness of the oil and soap sprays used were due partly 

 to the weakening effect of showers, and, in the case of the miscible oil, 

 to the hold-over effect of the insectifeide upon the eggs or the larvae 

 hatching from eggs during at least a ten-day period after sprajang. 



Incomplete as are the data presented in this paper, they indicate 

 an advantage that miscible oil sprays have over fish oil soap sprays 

 which is of a most practical, though subtle, nature. When growers of 

 Citrus appreciate that it is much more profitable, and not more expen- 

 sive, to spray their groves when the average number of Aleyrodids per 

 leaf is small, rather than large, as is now the custom, this advantage 

 will be even more valuable in postponing future blackening of the 

 trees and fruit by the sooty mould. 



References 



(1) Morrill and Back. White Flies Injurious to Citrus in Florida. U. S. Dept. 

 Agr., B. E. Bui. 92. 



(2) Morrill and Back. Natural Control of White Flies in Florida. U. S. Dept, 

 Agr., B. E. Bui. 102. 



(3) Morrill. Fumigation for the Citrus White Fly as Adapted to Florida Condi- 

 tions. U. S. Dept. Agr., B. E. Bui. 76. 



(4) Morrill and Yothers. Preparations for Winter Fumigation for the Citrus 

 White Fly. U. S. Dept. Agr., B. E. Circular 111. 



(5) Back. Sprays for White Fly. Florida Fruit & Produce News, vol. 2, No. 29. 

 April 15, 1910. 



(6) Yothers and Crossman. Recent Results of Compoimding Miscible Oils for 



Use in ControUing White Fly. Florida Grower, vol. 3, No. 27, 1911, p. 7. 



(7) Yothers. Recent Results of Spraying Experiments for the Control of the White 



Fly on Citrus. Proc. Fla. St. Hort. Soc. for 1911, pp. 53-59. 



(8) Yothers. The Effects of Oil Insecticides on Citrus Trees and Fruits. Jour. 

 EcoN. Ent., vol. 6, No. 2, 1913, pp. 161-164. 



(9) Yothers. Spraying for White Fhes in Florida. U. S. Dept. Agr., B. E. Circu- 

 lar 168, AprU, 1913. 



