210 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 14 



Since the foregoing species are apparently quite vulnerable, a problem 

 deserving serious attention is the value of this system of treatment in 

 combating such insects in comjrnercial plantings of apple and grape. 



The Pear Psylla 

 During the past summer a special effort was made to ascertain the 

 comparative effectiveness of various spraying mixtures and dusting 

 preparations in controlling psylla n\Tnphs. As the results, in general, 

 were quite similar one experiment is selected as typical. On June 3, 

 1920, a plat of thirty Bartlett trees, about fifteen years old, was sprayed 

 with bordeaux mixture (4-4-100) to which was added 6 pounds of 

 paste lead arsenate and 1 pint nicotine sulfate. Four gallons were 

 applied on the average to each tree. An adjoining plat of sixty trees 

 of the same variety was dusted on the following day with a mixture 

 composed of 50 pounds sulfur, 10 pounds lead arsenate, 5 pounds nicotine 

 sulfate, and 30 pounds powdered tobacco. About 2% pounds were 

 applied on the average to each tree. Before treatment the nymphs on 

 fifty tagged spurs on each plat were counted, and on the day following 

 the operation each of these spurs was re-examined and the nymphs 

 present recorded. The data are given in Table V. 



Table V — Comparative Effectiveness of SpRAyiNG axd Dusting Against Psylla Nymphs 



In this experiment, as with other similar efforts, the dust mixture 

 killed a goodly percentage of nymphs, but, as compared with spraying, 

 the treatment proved considerably less effective. The nymphs secreted 

 in the axils of the leaves and fruits and, heavily coated with honey dew, 

 displayed the greatest resistance. It was under such conditions that 

 the inferiority of dusting to spraying was most marked. 



In experiments with hibernating adults, spraying proved very much 

 superior to dust mixtures as measured by the number of adults dislodged 

 from the trees and the percentage killed by the treatment. 



The Currant Aphis and Four-Lined Bug 

 Mixtures containing 0.5 and 2.0 percent, nicotine produced complete 

 paralysis of currant aphids. With the opening of currant buds it became 

 increasingly difficult to do effective dusting because of the interference 

 of the dense foliage. 



