12 THE HOP APHIS IN THE PACIFIC REGION. 
collect on the uppermost leaves, seems evidence enough to establish 
the hop as a winter host of the hop aphis, at least in these localities. 
It has been thought possible that the hop aphis may hibernate 
upon some plants other than the plum, prune, sloe, and hop, and 
during this investigation many observations were made upon plants 
in the vicinity of the hops, for the winter eggs. While observing the 
winged migrants at Independence, Oreg., they were discovered upon 
cherry, alder, peach, and apple, and were found depositing young 
upon these plants. 
In order to see if the young would mature on the cherry, some in- 
fested leaves were placed in covered jelly glasses and the leaves 
renewed each day. These insects matured on cherry as rapidly as 
on plum, but as there were no males present they died without de- 
positing any eggs. Later observations upon the same trees at Inde- 
pendence, however, failed to reveal any eggs upon any but the plum, 
on which plant they were very numerous. Although no eggs were 
found on these trees, the fact that the aphides could grow to full size 
upon the cherry indicates that under some conditions this insect may 
hibernate on the various plants on which it was found at Independence. 
EMERGENCE FROM HIBERNATION. 
Whether the eggs are laid upon the plum, prune, sloe, or hop, the 
aphides emerge about the same time. The exact date was not ob- 
tained, but judging from the fact that full-grown aphides were ob- 
served April 23, and allowing 13 days for growth, they must have 
emerged from the egg about April 10. Again, allowing 26 da} T s for 
the two generations on the prune and May 24 as the date of the ap- 
pearance of the first winged insects, the eggs must have hatched by 
April 28. This assumption corresponds very closely with data ob- 
tained at Richfield Springs, N. Y., in 1888 by Mr. Theodore Pergande, 
who observed the emergence of the aphides from eggs on April 5, 16, 
and 18 and May 10. 
The insects which emerge from the sexual eggs are wingless vivip- 
arous females — " stem-mo thers," so-called. They are 1J to 2 milli- 
meters (y 1 ^ to -^2 inch) in length, whitish green in color, and have 
rather long antennae set on frontal tubercles, which are provided on 
the inner side with a tooth (see fig. 2). These toothed frontal tuber- 
cles are very characteristic of this species and serve well to identify it. 
METHOD OF REPRODUCTION. 
These viviparous insects, instead of depositing eggs, as do the sexual 
generations which appear in the fall, give birth to living young by a 
process called "budding." These young may be readily seen pro- 
truding from the tip of the abdomen. This is also the method of 
