366 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 12 



egg. The egg burster or elevated ridge on the meson of the cephahc 

 aspect of the head in both species disappears at the time the skin or 

 exuvium spHts and is shed, consequently it must be a part of the 

 embryonic membrane or exuvium. 



In both species the outer layer of the egg usually splits along the 

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

 sphtting of the outer layer of the egg is also characteristic of eggs of 

 other species of plant lice. A number of undetermined eggs of 

 plant lice found on various trees (willow, etc.) were examined during 

 March and their outer layers split in a manner similar to aphid eggs 

 found on apple trees. If aphid eggs in general are similar in con- 

 struction and behavior in hatching to aphid eggs on apple trees then 

 the response of various species of aphid eggs to environmental factors 

 might be the same. Under these conditions it is probable that evap- 

 orating factors have considerable influence on the percentage of hatch. 

 During the past season at New Brunswick the first eggs of A. avence 

 with a split outer shell were seen on February 10. The percentage of 

 eggs of A. avence showing this split condition continued to increase and 

 when the eggs started to hatch in large numbers on March 21, 35 to 

 40 per cent of the eggs showed a split outer shell and from 60 to 65 per 

 cent of the eggs hatched in 1919. 



The hatching period during 1919 lasted from March 21 until April 

 6. This prolonged period was due to the fact that on March 28, when 

 55 per cent of the eggs had hatched, a decided drop in the temperature 

 took place and this continued for five or six days, thus delaying the 

 completion of the hatching until April 3 to 5. 



The first eggs of A . pomi at New Brunswick with a split outer cov- 

 ering were seen on March 3 and on March 21, 25 to 35 per cent had 

 split their outer shells. A pomi started to hatch rapidly between 

 April 5 and 10 and the hatching period was completed by April 20. 

 From 50 to 55 per cent of the eggs of this species hatched in 1919. 

 The eggs of this species were found on first year wood and collected 

 from a young apple orchard near Lyons and Chester, N. J. It is pos- 

 sible that a few of them, not over 10 per cent, were eggs of A. avenoe 

 and A. sorbi. On April 22, the particular trees at Lyons from which 

 the majority of eggs were collected for experimental purposes were 

 examined and the young leaves were covered with aphides. After 

 observing several hundred insects, 4 per cent were A. avence, 7 per 

 cent were A. sorbi, and 89 per cent were A. pomi. Even though this 

 count is correct it is probable that many of the nymphs of A. avence 

 and A. sorbi seen on the terminal fruit buds came from eggs located 

 on the second year wood (second year wood was not used in experi- 

 ments with A. pomi). 



