THE MIGRATION OF THE APHIDIDAE AND THE AP- 
^PEARANGE OF THE SEXUAL FORMS AS AFFECTED 
BY THE RELATIVE LENGTH OF DAILY LIGHT EX¬ 
POSURE 4 
By S. Marcovitch 
Assistant Entomologist, Tennessee Agricultural Experiment Station 
INTRODUCTION 
It is generally stated in textbooks that on the setting in of cold weather 
there is produced in the aphids a generation of males and females. Tem¬ 
perature has been considered to be the determining factor in the appear¬ 
ance of the sexual forms. As to the factors which influence the early 
or late production of migratory forms, Matheson (15) 2 remarks that sug¬ 
gestions have not been made by any worker. 
During the course of the investigation of the strawberry root louse 
(Aphis forbesi Weed), in 1921, it was observed that large numbers of 
the sexes made their appearance in the laboratory on November 3, this 
being somewhat earlier than they appeared in the field. At this time 
of the year the air in the laboratory is warmer than that outside, so 
that the temperature factor did not seem to be the cause of their appear¬ 
ance. A copy of Gamer and Allard’s (6) work came to the writer’s 
attention just at this time, showing that flowering and fruiting of plants 
can be attained in certain varieties and species only when they are 
exposed to definite amounts of daily light such as obtain during certain 
seasons of the year. Plants and plant lice have this in common that 
sexual forms make their appearance only at certain definite periods; so 
it occurred to the writer that length of day was a factor which might 
influence the latter as well as the former. 
A word of explanation in regard to the life-history of plant lice may 
be in place hefe because of their peculiar mode of development. There 
are many variations and modifications in the different species, but in 
general it may be stated that the winter is passed in the egg stage, espe¬ 
cially in the more northern latitudes. In Tennessee the eggs hatch in 
the spring as early as February 12 into a form known as the stem-mother, 
which matures in from 8 to 14 days. The stem-mother is always wing¬ 
less and gives birth to living young parthenogenetically—that is, with¬ 
out the presence of males. This mode of reproduction continues until 
the fall, when the true males and females make their appearance. Upon 
mating, the eggs are deposited which carry the insect through the winter. 
There are many variations in the general life cycle as just stated. The 
second generation, that is, the progeny of the stem-mother, may . con^ 
sist mostly of winged forms which migrate to other plants of the same 
species or even to entirely different species (secondary host) widely 
separated from the original host. The migratory forms may also make 
their appearance in any subsequent generation. After several genera- 
1 Accepted! or publication. Jan. 2, 1924. 
* Reference is made by number (italic) to “Literature cited/' p. 522. 
journal of Agricultural Research, Vol. XXVII, No. 7 
Washington, D. C. Feb. 16,1924 
Key No. Teon.-* 
(513) 
