Ill 



atmospheric conditions and acts as a protective layer to conserve the 

 moisture content of the embryo ; if this outer layer be removed, the 

 eggs shrivel up completely in 24 hours under ordinary atmospheric 

 conditions. 



The percentage of eggs of A. avenae and A. pomi hatching under a 

 constant temperature of 80° F. varies with the moisture content of 

 the air. In dry air up to 4 per cent, of the eggs hatched ; in 22 per 

 cent, moisture up to 12 per cent, hatched ; in 63 per cent, moisture 

 20 per cent, hatched ; and in 100 per cent, moisture 36 to 46 percent, 

 hatched. This resjjonse to differences in moisture indicates that 

 drought or climates with low humidity probably have an important 

 influence on the percentage of eggs that hatch, and records from 

 various States bear out this conclusion. If this susceptibility in the 

 egg is particularly marked shortly prior to hatching, it would seem 

 probable that certain contact insecticides and chemicals would affect 

 the egg during this period. This has undoubtedly proved to be the 

 case with certain lime-sulphur solutions at winter strength, and crude 

 oil emulsion and other sprays have been successful in kiUing the Aphids 

 in the egg-stage when applied just before or as the buds were bursting. 

 The exact physical and chemical effect of various sprays on the egg is 

 still not fully understood. The chemical structure of the egg coverings 

 and the nature of the reactions which may occur between the egg and 

 the insecticide used are almost entirely unknown ; some of the 

 physical effects produced by various substances have, however, been 

 observed and these are briefly discussed. 



In order to kill the insects in the egg-stage, the material used must 

 prevent the nymph from hatching or should kill the nymph as it 

 hatches. Any substance that ^\dll harden the outer shell siiificiently to 

 prevent the emergence of the nymphs would be satisfactory. Lime- 

 sulphur apparently does this. A substance that will soften or dissolve 

 the outer layer and expose the pervious, pigmented layer imderneath 

 to evaporating factors such as wind, heat or dryness would destroy the 

 eggs ; a weak solution of crude carbolic acid apparently has the effect 

 of softening and disintegrating the outer shell. When eggs of A. pomi 

 were sprayed with a 2 per cent, solution of crude carbolic acid with 

 enough soap to break the surface tension of water, and placed in a 

 moist chamber, the brittle outer layer became soft and wrinkled in 

 about an hour and could easily be removed. Lime-sulphur and 

 possibly crude carbolic and various other substances have some 

 desiccating effect and probably extract the water content of the ovum 

 or embryo and thus prevent further development. A still more success- 

 ful ovicide would be a toxic substance that would penetrate the egg 

 coverings and attack the living embryo. The extent of such 

 penetration by various substances is difficult to determine. Another 

 possible means of control would be the discovery of some chemical 

 that would loosen the egg from the twig and cause it to fall to the 

 groimd. There is some indication that sodium hydroxide tends to 

 produce this result. 



The more successful contact insecticides and various chemicals have 

 been tried on the eggs of all three species. In every case some or all 

 of the eggs proved susceptible to the insecticide used, A. avenae being 

 apparently the most susceptible of the three species. A table gives 

 the percentage of eggs destroyed by various substances. Lime-sulphur, 



