14 



THE HOP APHIS IX THE PACIEIC REGION. 



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 migj - 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. 

 r. developing upon the hopvines during the summer, at Wat- 

 sonville. Cal.. by Prof. TV. T. Clarke, of the California Experiment 

 Station, in 1902: by Mr. Franz Eemisch. a1 Si az, Bohemia: by Mr. 

 H. X. Ord. at Independence. Oreg. : and by the writer at Santa E 

 Cal., in 1911. 



As previously stated, the winged migrants are weak fliers, but when 

 aided bv the wind mav travel some distance. Some individual- v. 



3L — The hop aphis: Winged female migrant. Mnch enlarged. (Original) 



found half a mile from the infested prune tree-. The infestation, how- 

 ever, decre - s as the distance from the alternate host inci 



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 f< _ but were in every i 



le distance from the ground. The lower 1 - were entirely 

 free from the winged forms. 



deposit: y< hjng. 



Upon reaching the hopvines these parthenogenetic migrant^ were 

 served giving birth to young, the number deposited by each indi- 

 vidual varying between 1 and B siss . in Table I. 





