982 
Journal of Agricultural Research 
Vol. V, No. 21 
conjunction with their observations they can very closely approximate 
the true conditions. 
In the diagram (fig. 2 ) the solid lines represent actual records. The 
hatched lines occurring at the beginning of the fifteenth to nineteenth 
generations are theoretical. They are necessitated by the fact that the 
earliest progeny was lost in some of these generations and it was necessary 
to continue with later offspring. The hatched lines at the end of the sev¬ 
eral generations are deduced by adding the average length of life to the 
date of last production of young. 
It will be noted that theoretically all the generations from and including 
the seventh should be expected to produce the sexes. It is quite proba¬ 
ble that such production occurs in nature, and that the sole reason sexes 
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Fig. 2.—Diagram showing the overlapping generations of the green apple aphis. 
were not obtained from the seventh, eighth, and ninth generations is that 
later members of these generations were not reared and bred from. 
FEEDING HABITS 
As noted previously, the stem mothers fed only on the exposed green 
of the bursting buds and tiny leaflets, as this was the only food available 
to them. Later generations preferred the leaf petioles and then the young, 
newly formed twigs, although some remained on the leaves. In cases 
where the latter were excessively downy, however, the young stages es¬ 
pecially appeared to find some difficulty in living on them. This char¬ 
acter of downiness seemed to be particularly unfavorable when occurring 
on the underside of the leaves. Later, when the twigs commenced to 
harden, the aphides migrated back to the underside of the leaves, and 
in the fall, at the time the sexes began to appear, practically no viviparous 
aphides were found in any other location on the trees. This selection of 
food occurred only when the numbers were comparatively small. In the 
case of excessive infestation, twigs, leaf petioles, and the underside of 
the leaves are attacked simultaneously. Occasionally a single aphis will 
be found feeding on the upper surface of a leaf, but these cases are so 
rare as to be almost negligible. 
