690 RoBerRT MATHESON 
prepared there have appeared two good biological accounts of this aphis, 
one by Brittain (1915b) and the other by Baker and Turner (1916 a.) 
The green apple aphis is the only species of plant lice which spends 
its entire life on the apple tree. This was shown by De Geer in 1773, 
but for some reason his interesting account remained unknown until 
within very recent years. The winter is passed in the egg stage. The 
eggs are found scattered over the succulent twigs and branches, usually 
in cracks or crevices or around the base of fruit spurs or leaf buds; in fact 
eggs may be found on almost any part of the branches when the lice are 
very abundant. 
Hatching of the eggs 
The eggs (Plate VII) hatch early in the spring, about the time when 
the flower buds show green at their tips or just a little later. The exact 
date on which the eggs began hatching at Ithaca in 1915 was April 21. 
This record is for eggs of this species which were laid the preceding autumn 
on seedling apple trees in rearing cages. ‘These trees were kept caged 
all winter under normal outdoor conditions. On April 22 hatching 
became more general, the lice appearing in great numbers. On the 26th, 
large numbers of the eggs were hatching and the first cast skins were 
found. This continued for several days, the last eggs on this tree hatching 
about May 1. It will thus be seen that for this species the eggs hatch 
over a considerable period, at least ten days in the case of the caged trees. 
From observations made under orchard conditions similar conclusions 
were drawn, the eggs hatching during a period of at least ten days. How- 
ever, the majority of the eggs hatch during the first few days, that is, 
at the time when the flower, buds are showing green. The number 
of eggs hatching after the first four or five days is not very large, but this 
depends much on weather conditions. Sudden cold weather may delay 
hatching or it may destroy the young lice before they leave the eggs. 
In the spring of 1916 eggs were observed hatching when the blossom 
buds showed pink, a very important consideration when the problem of 
control is taken into account. 
These observations are in agreement with those of other workers. 
Smith (1900a) found the hatching period in New Jersey to extend over 
at least fifteen days (from April 15 to April 30). Gillette and Taylor 
(1908) state that in Colorado the eggs begin hatching before the apple 
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