SOME STUDIES ON THE INFLUENCE OF ENVIRON- 

 MENTAL FACTORS ON THE HATCHING OF THE 

 EGGS OF APHIS AVEN^ FABRICIUS AND 

 APHIS POMI DeGEER.* 



By Alvah Peterson. 

 INTRODUCTION. 



The eggs of Aphis avence Fabricius^ and Aphis pomi DeGeer 

 have two distinct layers in the egg shell (Figures 1 to 4). The 

 outer layer, when the eggs are first deposited, is transparent, 

 soft and glutinous, but it soon hardens upon exposure to 

 weather conditions and becomes semi-transparent, toughened, 

 dry and decidedly impervious to water. The inner layer is a 

 soft, elastic, black membrane and decidedly pervious to water. 



The outer layer usually splits (Figures 2 and 3) along the 

 dorso-mesal line a number of days before the nymph emerges. 

 The above structure and splitting of the outer layer is also 

 characteristic of the eggs of other species of plant lice; a species 

 of Lachmis, which deposits its eggs on the needles of whitepine, 

 another aphid which deposits its eggs about the buds of weeping 

 willow and at least one species of aphid which deposits its eggs 

 in ant nests. I am indebted to Mr. J. L. King for furnishing 

 me with eggs from an ant nest. The time and percentage of 

 the splitting of the outer layer and the hatching is dependent 

 upon environmental conditions, particularly temperature and 

 moisture. The outer layer of the eggs of A. avencE may start 

 to split in February (February 10, 1919), while the splitting of 

 the eggs of A. pomi usually does not start until March, (March 

 3, 1919). The eggs of A. avencB usually hatch rapidly the last 

 week in March and the eggs of A. pomi usually hatch rapidly 

 somewhere between April 5 to 15th. The above observations 

 are true for New Brunswick, N. J. For further information 

 on the time and percentage of splitting and hatching, see 

 Tables 4 and 5 and references. 



*Contribution from the Entomological Laboratory of Rutgers College, State 

 University of New Jersey, New Brunswick, N. J. 



^ A phis avencB Fabricius is Rhopalosiphum prunifolicB Fitch according to A. C. 

 Baker and W. F. Turner. 



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