l 73 
Bugs, Cicadas, Aphids, and Scale-insects 
mm. in width, an easy calculation shows that these conceivably possible de¬ 
scendants of a single female would, if closely placed end to end, form a proces¬ 
sion seven million eight hundred and fifty thousand 
miles in length; or they would make a belt or strip 
ten feet wide and two hundred and thirty miles long.” 
The remarkable plasticity of the aphids as re¬ 
gards their possession or lack of wings and, on the 
physiological side, their reproduction agamically or 
sexually, introduces certain unusual conditions into 
their life-history. Although each species is likely 
to present idiosyncrasies of its own, a fair example 
of the course of aphid life through a season may 
be outlined as follows: In spring there hatch, from 
eggs which have been laid the fall before, wingless 
females, called stem-mothers, which produce young 
agamically (i.e.; from unfertilized eggs) either by 
giving birth to them in active free condition or by 
laying eggs. From these eggs hatch wingless females 
which produce in turn other agamic broods of wing¬ 
less females. But at any time in the course of these 
successive agamic generations either all or a part of 
the individuals of a brood may be winged, and these 
winged females fly away to other plants and there 
found new colonies which continue the series of 
agamic generations. But toward the end of the 
season, when the first cold weather announces the 
approaching winter, broods, still parthenogenetically 
produced, of sexed individuals, both males and fe¬ 
males appear. “The males may be either winged 
or wingless, but these true females are always wing¬ 
less.” These individuals mate, and each female 
produces a single large egg which passes over 
the winter to give birth in the following spring to a 
wingless stem-mother—that one which begins the 
spring series of parthenogenetic generations. The unfertilized eggs, called 
pseud-ova, produced in numbers by the spring and summer agamic mothers 
(from which eggs the young frequently emerge while the eggs are still in the 
body of the mother) should not be confused with the single fertilized egg 
laid in the late fall by the mated females of the sexed generation. Although 
these two sorts of eggs are alike in their earliest stages in the ovaries of the 
females, differences very soon occur, the embryo in the pseud-ovum begin¬ 
ning to develop before the formation of its own egg is properly completed. 
Fig. 246.—Bodies of 
aphids which have been 
killed by Hymenopter- 
ous parasites, the adult 
parasitic flies having 
emerged from the small 
circular holes. (En¬ 
larged.) 
