558 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 10 



the air. A brief summary of a number of experiments shows that in 

 dry air to 4 per cent of the eggs hatched, in 22 per cent moisture 

 to 12 per cent hatched, in 63 per cent moisture 20 per cent hatched 

 and in 100 per cent moisture 36 to 46 per cent hatched. This response 

 of the eggs to differences in moisture indicates that drought or cUmates 

 with low humidity probably have an important influence on the 

 percentage of hatch. It has been recorded for Colorado that approxi- 

 mately only 1 per cent of the eggs of A . pomi hatch while the percent- 

 age of hatch for all three species at New Brunswick, N. J., ran about 

 25 per cent for A. pomi and A. sorhi (mixed together) and 50 per cent 

 for A. avena' and the relative humidity for New Jersey is higher than 

 that of Colorado. 



If the eggs are weak in structure and susceptible to differences in 

 moisture, particularly during the hatching period and possibly a few 

 weeks previous to this time, it would seem feasible to assume that cer- 

 tain contact insecticides and various chemicals should effect the egg 

 during this period. This is unquestionably the case for a number of 

 investigators using lime-sulphur at winter strength; crude oil emulsion 

 and other sprays have met with success in killing the aphis in the egg 

 stage when the spray was applied late in the season just before or as 

 the buds were bursting. 



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

 egg have never been explained and, so far as known, is still more or 

 less a mystery. Very little is known concerning the chemical structure 

 of the egg coverings or the nature of the reactions which may occur 

 between the egg and the insecticide used, however, some of the physical 

 effects produced by various substances have been noted and these are 

 discussed briefly. 



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

 prevent the nymph from hatching or it may be of such a nature as to 

 kill the nymph as it hatches. The preventive, from a physical stand- 

 point, may act in several ways. Any substance which will harden the 

 outer semi-transparent shell and thus make it impossible for the 

 nymphs to emerge would be satisfactory. Lime-sulphur apparently 

 hardens the outer covering, at least it was noted that a large number of 

 treated eggs did not completely collapse and in many cases the outer 

 layer retained its normal shape while the pigmented layer and the 

 contents of the embryo within was completely shrivelled. 



Any substance which will soften or dissolve the outer layer and 

 thus expose the pervious, inner, pigmented layer to evaporating factors 

 such as wind, heat or low humidity would make a satisfactory control. 

 A weak solution of crude carbohc acid will soften and apparently 

 disintegrate the outer shell. In one experiment, the eggs of A. pomi 



