October, '19] PETERSON: APHID EGGS 367 



Methods 



Whenever material was needed for experimental purposes, collec- 

 tions were made from the above mentioned orchards and the material 

 was kept out-of-doors all the time and exposed to all conditions of 

 the weather except for the few minutes required to examine the eggs 

 under a binocular microscope in order that all the abnormal appearing 

 €ggs (shriveled, hatched or light colored eggs) might be removed and 

 the normal eggs counted. A string tag was placed on each twig (8 to 

 12 inches long) and on it was written the number of the experiment, 

 total number of normal eggs, species, and source of the material. 



The number of normal eggs of A. avence and A. pomi used in each 

 spraying experiment in 1918-1919 was 200 to 300 and 300 to 500, 

 respectively, while in 1917-1918 only 100 to 150 eggs were used. This 

 increase over previous years reduced the possibility of experimental 

 error to a minimum. The consistent regularity of the plotted lines 

 on the charts shows the minimum nature of the experimental error in 

 the spraying experiments for 1918-1919. The eggs of A. avence were 

 sprayed at regular intervals throughout the season; on December 7, 



1918, January 9, February 10, March 1, March 10 and March 21, 



1919, while the eggs of A. pomi were sprayed on February 18, March 3, 

 March 12 and March 21, 1919. No dormant sprays were applied 

 after March 21 because at that time the fruit buds showed green and 

 were in the proper stage for the application of a delayed dormant 

 spray. Any recommended dormant spray applied after April 3 in 

 the southern part of New Jersey in 1919 would have injured most 

 varieties of apple trees. Furthermore, many hatched nymphs after 

 April 3 were protected by the young leaves. 



The following substances were used at varying strengths and some 

 in combination with each other in the spraying experiments: con- 

 centrated liquid lime-sulfur (Mcchling Bros. Mfg. Co., Camden, N. J.), 

 dry hme-sulfur (The Sherwin-Williams Co., Newark, N. J.), barium- 

 sulfur ("B. T. S.," General Chemical Co., New York City), sodium- 

 sulfur ("Soluble sulphur," Niagara Sprayer Co., Middleport, N. Y.), 

 sodium sulfo-carbonatc (The Dow Chemical Co., Midland, Mich.), 

 hydrated lime, miscible oil ("Scalecide," B. G. Pratt Co., New York 

 City), nicotine ("Black Leaf 40," The Kentucky Tobacco Product 

 Co., Louisville, Ky.), fish oil soap, paste form (Capstone Mfg., New- 

 ark, N. J.), "Fels Naphtha" laundry soap, linseed oil, cotton seed oil 

 crude carbolic acid, cresol U. S. P., etc. All of the sprays wore applied 

 to the twigs by means of a small hand atoinizor connected with a foot 

 pump. The twigs were held several inches from the tip of the atomizer 

 and all sides of each twig were thorouglily hit once, thus coating every 

 egg. After all the twig.s of one experiment were sprayed they were 



