10 BULLETIN 774, U. S. DEPARTMENT OF AGRICULTURE. 



have been observed on the former in swampy regions, sometimes 

 removed many miles from any winter hosts. On the other hand, 

 Typha grows in abundance close to prune orchards and yet, con- 

 sidering the enormous production of spring migrants throughout 

 May, June, and July, the later infestations on near-by Typha are in 

 the aggregate exceedingly small. The writer has seen clumps of Typha 

 latifolia, growing not 30 feet from prune trees on each of which 

 thousands of winged forms were being developed, receive only a 

 few dozen migrants and perhaps have not over 6 out of 100 blades 

 colonized by their progeny. It is true that when once established 

 a colony on Typha increases rapidly, but it is also evident that the 

 migrant fails to do justice to her reproductive capabilities on this 

 plant. 



That the migrants fly long distances to seek their alternate hosts, 

 especially Phragmites, is the conviction of the writer. 



The spring migrants settle on Typha near the apex of a strongly- 

 growing blade and station themselves parallel to its long axis. The 

 wingless forms later take up this same position. After the migrants 

 have extruded a few young the whitish meal is excreted in greater 

 abundance. On Phragmites the colonies are similarly disposed. On 

 three occasions the writer observed heavy summer infestations on 

 the reed Phragmites communis L. On July 5, 1917, along the banks 

 of the San Joaquin River about 15 miles west of Stockton, Cal., this 

 plant was heavily attacked. Among the colonies occurred a few 

 pupaB and winged forms of a winged summer form. Typha latifolla 

 growing among the infested reeds was not attacked. On August 

 13, 1917, at Benicia, Cal., clumps of reeds growing in swampy ground 

 near San Francisco Bay bore heavy infestations of the aphis and 

 the summer winged form was abundant. Plants of Typha grow- 

 ing among the clumps of Phragmites were sparingly infested. On 

 May 15, 1918, heavy infestations were observed on Phragmites com- 

 munis growing on the west shore of the Salton Sea, in southern 

 California. 



These observations indicate that Phragmites is the preferred 

 summer host plant. 



The summer winged aphids serve to distribute the species among 

 the reeds. They do not differ in appearance or structure from the 

 spring migrants produced on the winter hosts. 



Fall migrants appeared both in 1915 and 1916 on Typha about 

 October 15, and continued until the end of November. Males ap- 

 peared the last week of October and throughout November. The 

 small yellowish pupae of the latter are easily distinguishable on the 

 cat-tails from the green pupse of the fall migrant. Mature fall 

 migrants remained on the summer host for a day or two before 

 departing. 



