BULLETIN 100, U. S. DEPARTMENT OF AGRICULTURE. 
LIFE HISTORY AND TECHNICAL DESCRIPTIONS. 
The Viviparous or Asexual Forms. 
When the young stem-mother is ready to emerge in the spring she 
causes the shell of the winter egg to burst with a longitudinal slit on 
the dorsal surface from the micropylar end. (See fig. 1.) Egress is 
performed head first, and antennae and legs are requisitioned by the 
young larva in worming its way out of the shell. While the process 
of emerging, which occupies half an hour or more, is taking place, the 
aphis assumes an erect position at right angles to the long axis of the 
egg. After the exit of the young the eggshell has a large triangular 
hole at the micropylar end. 
As soon as the buds begin to swell in early spring these stem-mothers 
hatch and continue hatching until the leaves have fully opened out, at 
which time all will have issued from the egg. The earliest plant-lice 
to emerge may be seen wandering over the bare twigs and buds, 
apparently feeding a little upon the scales protecting the unopened 
buds, but not showing much growth until the buds 
have opened and can afford nourishment. 
Undoubtedly many of the aphides that hatch 
early die of ill nourishment, and some of these do 
not attain their full development for six or seven 
weeks, while those hatching later and finding 
tender food in abundance become full grown at 
the end of five weeks. Certain it is that on a 
particular tree the stem-mothers all became 
winged almost simultaneously. On trees which 
leaf early the stem-mothers will begin emerging [from the egg as 
early as February 15, but on the Franquette and such late varie- 
ties no aphides will be found until in April. Immediately after 
hatching the lice seek the buds -or young leaves. In the former case 
the aphides crawl in between the scales, but on the leaves they 
appear on the lower or exposed side, notwithstanding the fact that 
much better protection is afforded by the upper, as yet unfolded, sur- 
face which at that time is almost entirely hidden from view. Possibly 
the sticky character of the upper surface of the leaves repels them. 
Table I indicates the fife cycle of four stem-mothers which hatched 
after the buds had opened. 
Table I.'- — Period of development of the stem-mother of Chromaphis juglandicola, San 
Jose, Cal., 1912. 
Fig. 1. — Chromaphis juglandi- 
cola: Group of eggs, three 
lowest hatched. Twenty 
times natural size. (Origi- 
nal.) 
No. of individual. 
Date of 
hatching. 
Date of 
acquiring 
wings. 
Period from 
hatching to 
maturity. 
1 
Mar. 24 
24 
24 
24 
Apr. 28 
28 
28 
29 
Days. 
35 
35 
35 
36 
2 
3 
4 
Average period . 
35.25 
