Mar. 1, 1925 
The Strawberry Root Lome in Tennessee 
447 
In midsummer it is difficult to find any 
lice at all, owing to the activities of 
their natural enemies. Both young 
and mature forms were present on the 
rootlets as early as April 11. 
THE TRUE SEXES 
The true males and females make 
their appearance in Tennessee late in 
October, and may be found on the 
plants until February, when the eggs 
are ready to hatch. After maturing, 
the females deposit eggs, which carry 
the species over the winter. Although 
viviparous females may be present on 
the plants as late as December, they 
invariably die and do not assist in the 
reproduction of the species. 
The males are small, wingless, and 
comparatively few in number. On one 
leaf pedicel there were counted 2 males 
and 22 oviparous females. The ovip¬ 
arous females can be readily recog¬ 
nized by their elongate appearance 
(pi. 1, B) and lighter color, caused by 
yellowish eggs showing through the 
chitin. In 1922 the first eggs were laid 
on November 9, although active egg 
laying does not begin until December. 
The eggs when first deposited are 
orange colored, and it is not until 
several days later that the character¬ 
istic shiny black color is assumed. The 
number of eggs deposited by a single 
female varies from four to eight. 
FACTORS WHICH INFLUENCE THE AP¬ 
PEARANCE OF THE SEXES 
With remarkably few exceptions, the 
true sexes in plant lice, including Aphis 
forbesi , make their appearance in the 
North Temperate Zone in the fall of 
the year and pass the winter in the egg 
stage. In the more southern localities 
plant lice generally reproduce through¬ 
out the year without the appearance 
of true sexes or eggs. Therefore, it is 
natural to conclude that the factor 
stimulating the formation of true sexes 
must be temperature; and such was 
assumed to be the case until it was 
noticed that the sexes made their ap¬ 
pearance somewhat earlier on a plant 
growing in the laboratory than they 
did in the field. The laboratory air is 
warmer than that outside in the latter 
part of October and November, so that 
as far as the factor of temperature is 
concerned there seemed to be no cor¬ 
relation. There is, however, a marked 
difference between the intensity and 
duration of daily light exposure in the 
laboratory and the field. Garner and 
Allard * 1 have shown that the length 
of daily light exposure influences the 
flowering and fruiting of plants, and 
since plant lice and plants both have 
asexual and sexual stages, which make 
their appearance at stated intervals, 
it occurred to the writer that possibly 
light rather than temperature was the 
determining factor in the formation 
of the sexes, and such was found to 
be the case. 
PRODUCTION OF TRUE SEXES AND ITS 
RELATION TO THE SHORT DAYS OF 
FALL 
One of the familiar phenomena of 
the Temperate Zone in the autumn is 
the shortening of the length of day. 
To create an artificial short day the 
potted plants used in the experiments 
were placed out of doors in a dark, 
ventilated chamber at 5 p. m. and 
kept there until 9.30 the next morning, 
when they were removed and placed in 
the light. The plants and plant lice 
were thus subjected each day to seven 
and one-half hours of light exposure. 
Any response on the part of the insects 
could hardly be attributed to. tem¬ 
perature, since the temperature inside 
was but 2° to 3° F. higher than that 
outside. Single potted plants were also 
darkened by having inverted over them 
a larger pot or box. 
In 1922 the plant with lice was sub¬ 
jected to a short day, beginning May 
23. The first males and oviparous 
females were observed to make their 
appearance on September 18. Eggs 
were deposited on September 22, this 
being about seven weeks earlier than 
the first eggs are deposited in the field. 
1 Garnar, W. W., and Allard, H. S. effect of the relative length of day and night and 
OTHER FACTORS OF THE ENVIRONMENT ON GROWTH AND REPRODUCTION IN PLANTS. Join*. Agr. Research 18: 
553-606, illus. 1920. 
EXPLANATORY LEGEND FOR PLATE 3 
A. — Diaeretus fuscicornis 
B. — Paragus tibialis: Egg 
C —Paragus tibialis: Egg under high magnification showing sculpturing 
D. — Paragus tibialis: Caudal appendage 
E. — Aphis forbesi: Cornicle of oviparous female 
F. — Aphis forbesi: Cornicle of wingless viviparous female 
G. — Aphis forbesi: Antenna of wingless viviparous female 
H. — Aphis forbesi: Antenna of oviparous female. 
I. —Aphis forbesi: Hind tibia of oviparous female 
J. — Aphis forbesi: Antenna of first instar stem-mother 
K. — Aphis forbesi: Cornicle of first instar stem-mother 
