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 
pupe and winged forms of a winged summer form. Zypha latifolia 
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 pup of the latter are easily distinguishable on the 
cat-tails from the green pup of the fall migrant. Mature fall 
migrants remained on the summer host for a day or two —_ 
departing. 
