F<fb. 16, X924 
Effect of Light Exposure on Migration in Aphids 519 
March 26, 1923, the eggs began to hatch and the stem-mothers matured 
about April 5, inside the laboratory, under a long day of 15 hours of arti¬ 
ficial light. The second generation matured April 16, and was wingless. 
Winged forms, consisting of the third generation, appeared in large 
numbers on April 24 on the plant kept under a long day, whereas under 
similar temperature and humidity conditions, only two winged forms 
appeared in the third generation on an apple seedling kept in the labora¬ 
tory away from artificial light. 
Similarly 10 generations were reared on apple by June 12, without more 
than two or three winged forms appearing in each generation, simply by 
keeping the seedlings indoors under subdued light growing in plain tap 
water and giving each generation a new plant. These seedlings were 
often yellowish and weak-looking, because of lack of nourishment, and 
yet the winged forms appeared sparingly. When the seedlings were 
allowed to become crowded, however, and under similar conditions, the 
winged forms became very numerous, so that it appears as if crowding 
were a factor that induces the formation of winged forms. No doubt 
many more than 10 generations could have been reared on apple, but 
because of the writer’s absence from the office the plants died. 
Beginning with April 24, a narrow-leaved plantain with migrants was 
placed in the dark chamber. Winged forms that may have been summer 
migrants appeared as early as May 21. On June 6 winged forms from 
plantain kept in the dark chamber were placed on apple. They fed and 
■deposited young, which lived on apple six days. Baker (3) has determined 
that with certain species the oviparous forms require hard, dry leaves 
to mature on, such as appear in autumn when the leaves are falling. 
It is very likely that for this reason the young oviparous females failed 
to mature, since all the apple leaves are very succulent in May. The 
appearance of the sexual forms is summarized in Table II. 
Table II .—Summary of the appearance of the sexual forms when subjected to a short day 
Date of eggs 
hatching. 
Date of transfer to dark 
chamber. 
Date of 
appearance 
of sexual 
forms. 
Date of normal appear* 
ance of sexual forms. 
Aphis forbesi . 
Feb. 16 
Feb. 23. 
May 7 
Oct. 20 to Nov. 15. 
Aphis forbest. .. 
Mar. 21. 
May 12 
Do. 
Aphis rumicis .. 
Mar. 9 
Apr. 17 (on curled 
dock). 
June 6 
October. 
Capitophorus hippo - 
phaes. 
Feb. 27 
Apr. 10 (on smart- 
weed). 
June 2 
Do. 
Aphis sorbi . 
Mar. 26 
Apr. 24 (on plan¬ 
tain). 
June 12 
October to No¬ 
vember. 
Aphis viburnicola Gill.—This species passes the winter on the common 
snowball (Viburnum opulus ), but its alternate host has so far not been 
discovered. The aphid occurs in Tennessee, although it is not common. 
Eggs received through the kindness of Professors Gillette and Ruggle 9 
hatched on March 12. The stem-mothers became full-grown March 26, 
and it was not until April 16 that they became full-grown out of doors. 
It is generally stated in the literature that all of the second generation 
acquire their wings and leave the snowball. With young snowball 
plants kept under a long-day and a short-day, the winged forms appeared 
