1920] 



Peterson: Hatching of Aphid Eggs 



397 



1919 it rained more than half of the fourteen days previous to 

 hatching and 50 to 65 per cent of the eggs hatched, while in 1918 

 and 1920 it only rained three and five days out of fourteen, and 

 30 to 40 per cent of the eggs hatched. 



It is a well known fact that evaporating factors are usually 

 low during rainy and cloudy weather and high when the sun 

 shines. Furthermore, we have learned from the moisture 

 control experiments that low evaporation (high moisture content 

 of air) produces a large percentage of hatch, while high evapo- 

 ration (low moisture content of air) produces a low percentage 

 of hatch. From these observations we may conclude that the 



TABLE IV. 



Relationship between the amount of rainfall (moisture index) 14 days before 

 hatching and percentage of hatch and split shells of eggs of A . avencB at New 

 Bninswick, N. J. 



weather conditions for the respective years influenced the 

 percentage of hatch. In other words, wet weather during the 

 ten to fourteen days previous to hatching permits a greater 

 number of eggs to hatch than dry weather during the same 

 period. 



Evaporating factors also appear to determine the rate of 

 split in the outside coating of the eggs. Comparing the rate 

 of split in the outer coats for the two extremely different seasons 

 of 1918 and 1919 it will be noted that in the dry season of 1918, 

 45 to 50 per cent of the eggs had split their outer coats at the 

 time of hatching and only 30 per cent eventually hatched. In 

 other words, 15 to 20 per cent or more of the eggs with split 

 outer coats never hatched. During the wet season of 1919 the 

 reverse was true, only 35 to 40 per cent of the eggs showed a 

 split outer coat at the time of hatching and 50 to 65 per cent 



