LIFE HISTORY. 
17 
average number of young (3.3 per day) over an average period of 
19 days, would give birth to 63 aphides. 
At this rate of reproduction, provided that none of the aphides 
were destroyed before they had lived an average life, one winged 
aphis which settles on the hop in the spring would at the end 
of the fifth generation be the parent of 4,068,989,826 living aphides. 
These aphides would weigh 2,152 pounds. From these figures the 
very sudden and extensive infestations by this insect are readily 
explained. 
THE FALL MIGRANTS. 
The nymphs of the fall migrants (fig. 6) became winged in the breed- 
ing cages at Perkins, Cal. , on Au- 
gust 26 and in the field August 
28. Migrants were observed 
upon plum at Independence, 
Oreg., September 22, 1912. 
Young were being deposited 
there and upon the next visit 
to the locality, October 16, large 
numbers of male aphides were 
observed copulating with the 
sexual females that had been 
deposited by the migrants. 
Many eggs were also present at 
this time. 
THE WINTER EGG. 
The winter egg, when first 
deposited, is a shiny-green ob- 
ject, ovate in shape, and a little 
smaller than the head of a pin 
(J mm. in length) . Soon, how- 
ever, it turns dark green and 
then black and appears as a shiny-black point (PI. I, fig. 2) on the 
branch of the alternate host plant. 
The eggs are usually deposited close around the buds or on the rough 
leaf scars, but may sometimes be found upon the smooth parts of 
the twigs. 
THE LIFE CYCLE. 
The entire fife cycle where the writer's observations were made is 
as follows : Two generations occur on the alternate host, the second 
one being winged. Five and six generations occur on the hop, a 
part of the fifth becoming winged and depositing young upon the 
74956°— Bull. 111—13 3 
Fig. 6.— The hop aphis: Nymph, showing wing-pads. 
Greatly enlarged. (Original.) 
