NATURAL ENEMIES. 
103 
The development of the embryo can be observed in a general way, 
with a hand lens, up to and including the sixth stage. This stage is 
reached, under favorable weather conditions (50° 
to 75° F.), in about three days. 
A large number of embryos are nearly or quite 
half grown by the time freezing weather begins, 
growth starting again with the first warm days 
of February. We have noted a revolution of the 
embryo within the egg, and this revolution takes 
place between figures 1 and 2 of Plate VII. Eggs 
begin to hatch by the last week in March, the 
typical appearance of the abandoned eggshell being shown in text 
figure 18. The number of stem mothers to appear in spring depends 
to a large extent upon the temperature of the preceding fall. 
Abbreviations Used in Plates I II- VII. 
mesoderm. 
Fig. 18.— The spring 
grain-aphis: Shell of 
egg after young stem- 
mother has emerged. 
Greatly enlarged. 
(Original.) 
A., anterior pole. 
ab 1 , ab 2 , etc., abdominal segment 
ab. r. abdominal region. 
am., amnion. 
app., appendage. 
at., antenna. 
b. c, blastoderm cell. 
&., blastoderm. 
c. I., cephalic lobes. 
d. o., dorsal organ. 
ec, ectoderm. 
en., entoderm. 
g. b., germ band. 
I., labrum. 
lab., labium. 
md., mandible. 
mx., maxilla. 
o., fundament of ovary. 
o. y., ovarian yolk, 
p., posterior pole. 
p. o., "polar organ." 
p.p., peripheral protoplasm. 
p. y., primary yolk. 
pcd., proctodeum. 
s., serosa. 
s. g., salivary gland. 
st., stomodseum. 
th. app 1 , 2 , etc., thoracic appendages. 
th. r., thoracic region. 
y. c, yolk cells. 
NATURAL ENEMIES. 
Toxoptera graminum is beset by a host of foes, without which we 
would be powerless to combat it. These enemies naturally group 
themselves into two classes: First, insects that develop within the 
body of the " green bug" and are termed true parasites; secondly, 
those foes that feed upon them externally or that take them directly 
into their bodies. These latter are termed predatory enemies. Under 
the true parasites we have Aphidius testaceipes Cress., Aphidius ave- 
naphis Fitch, Aphidius confusus Ashm., Aplielinus mali lIold.,ApJie- 
linus nigritus How., and Aplielinus semiflavus How., all of which are 
minute four- winged flies; under predatory enemies there are lady- 
beetles, syrphids, and cecidomyiids (two-winged flies), lacewing flies, 
and birds. Besides these, there are secondary parasites, or those that 
prey upon the true parasites of Toxoptera. These latter are as truly 
our enemies as are Toxoptera. 
