14 
THE HOP APHIS IX THE PACIFIC BEGlOX. 
can crawl from one to the other. The winged forms, therefore, are 
the only ones that migrate during the spring and early summer. 
In the fall the winged form (fig. 3) that produces the sexual female 
migrates from the hop to its winter host — the plum, prune, sloe, or 
hop — and later the winged male migrates to the plant on which the 
sexual female awaits fertilization. 
In the rearing cages and in the field during 1912 winged forms did 
not appear except as noted above. Winged forms were observed, 
however, developing upon the hopvines during the summer, at Wat- 
sonville, Cal., by Prof. W. T. Clarke, of the California Experiment 
Station, in 1902; by Mr. Franz Remisch, at Saaz, Bohemia; by Mr. 
H. N. Ord, at Independence, Oreg.; and by the writer at Santa Rosa, 
Cal, in 1911. 
As previously stated, the winged migrants are weak fliers, but when 
aided by the wind may travel some distance. Some individuals were 
Fig. 3.— The hop aphis: Winged female migrant. Much enlarged. (Original.) 
found half a mile from the infested prune trees. The infestation, how- 
ever, decreases as the distance from the alternate host increases. 
It was observed that more migrants collect upon the taller vines 
and the upper, newly expanded leaves of the other vines than upon 
the lower matured leaves. Very few winged aphides were observed 
on the fully expanded and hardened foliage, but were in every case 
some distance from the ground. The lower leaves were entirely 
free from the winged forms. 
DEPOSITION OF YOUNG. 
Upon reaching the hopvines these parthenogenetic migrants were 
observed giving birth to young, the number deposited by each indi- 
vidual varying between 1 and 8, as is shown in Table I. 
