22 Bulletin 332 



early part of March. When the nymphs were emerging (March 

 •31 to April 5) the rate of emergence was influenced by the tempera- 

 ture. On warm days the greatest number came out. The eggs of 

 A. avenm started to hatch on March 21 during the past season, 

 while in 1917 the first nymphs were seen on ^lareh 28. This dif- 

 ference is undoubtedly due to the difference in the temperature 

 mentioned above for the last two weeks in March for 1917 and 1918. 

 After the nymphs have emerged they are somewhat susceptible 

 to low temperatures. At least it was noted that on April 6, 1918, 

 in many unsprayed orchards, especially around Riverton, N. J., 

 the nymphs of A. aveim were very abundant, each bud on some 

 trees showing ten or more. On April 9-11 a severe drop in tem- 

 perature took place (enough to frost the edges of the small pro- 

 truding leaves), and a heavy snow and sleet storm accompanied 

 the change in temperature. On April 18 these trees were examined 

 and the heavy infestation was reduced below the danger point; in 

 fact, in some orchards adjacent to the Delaware river no aphides 

 could be found. The results of spraying experiments in this section 

 of the state and likewise in other portions during the past season 

 were not as striking as in 1917, on account of the storm. Possibly 

 the sleet and snow were as beneficial in killing the nymphs as the 

 cold weather. 



Contact Insecticides and Other Chemicals 



The foregoing morphological and ecological study of the eggs 

 of apple plant lice shows conclusively that they are not as firm and 

 impenetrable as some entomologists would have us believe, and 

 furthermore they are especially susceptible to differences in moisture 

 and temperature a few weeks previous to the emergence of the 

 nymph and also as the nymph emerges. These facts naturally lead 

 us to assume that certain common contact insecticides and various 

 chemicals applied just before the nymphs emerge should affect the 

 eggs and cut down the percentage of hatch. This is unquestionably 

 the case, for a number of investigators using lime-sulfur at winter 

 strength, crude oil emulsion and other sprays have met with success 

 in killing the aphid in the egg stage when the spray was applied 

 late in the season, in most cases just as the buds Avere bursting. A 

 brief review of these investigations has been made by P. R. Jones 

 (12). Dr. T. J. Headlce's experiments with lime-sulfur in 191G 

 at John Barclay's orchard also show that the rosy aphis, A. sorhi, 

 is killed in the egg stage. 



The exact physical and chemical effect (»(" the various sprays 

 on the egg has never been explained and, so far as is known, is 

 still more or less a mystery. In order to understand the chemical 

 reaction of various substances on llu- egg-.shell, it is necessary lo 



