THE MEALY PLUM. APHIS. 11 
Although migrations from Typha were traced with apparent cer- 
tainty in the fall of 1915, in the following year so few fall migrants 
were produced on local Typha under observation that they were out 
of all proportion to the great numbers of winged forms which began 
to appear in the prune orchards near Walnut Creek toward the end 
of October, and it was certain that the great majority of migrants 
were coming from a considerable distance. 
THE SUMMER WINGLESS FORMS. . 
DESCRIPTION. 
Newiy hatched.—Similar to that of spring wingless form, but more yellowish. 
Form elongate. 
Adulf—in color similar to those of spring wingless, but smaller in size and 
narrower in shape. 
Antenns about two-thirds body length. Comparative measurements as fol- 
lows: J, 0.08 mm.; II, 0.045; III, 0.26; IV, 0.16; V, 0.155; VI, 0.40 (0.08 plus 
0.32). Beak eeohtag second cox, 0.26 mm. long. Cornicles more cylindrical 
than in spring wingless form, inconspicuously imbricated, 0.07 mm. long. Style 
0.135 mm. long, shaped as in spring wingless form. Length of body, 1.6 to 2 
mm.; width of body, 0.65 mm. 
Measurements from specimens of what appears to be H. arundinis collected 
in April on Arundo in Peru by Mr. E. W. Rust were noticeably greater, but simi- 
lar in proportions. 
The lateral tubercles are inconspicuous. 
DURATION OF STAGES. 
Eighteen first-generation (progeny of migrant) individuals in the 
period May 29-August 20 matured on Typha in an average of 14.6 
days, the period of growth ranging from 12 to 18 days. Between 
June 17 and July 30, 15 aphids of the second and third summer gen- 
erations developed in an average of 15.8 days, with a range of from 
9 to 18 days, while 17 fourth-generation individuals developing 
between July 26 and August 27 averaged 12.2 days, with a range of 
from 9 to 16 days. Aphids maturing in September developed in an 
average of 14 days. All the individuals recorded above were wingless. 
There is apparently a maximum of as many as 10 wingless summer 
generations and a mimimum of 3. Molts occurred about as in the 
spring wingless forms. 
HABITS OF SUMMER WINGLESS FORMS. 
Colonies are located on both sides of the blades, chiefly on the outer 
half, occasionally on the basal half of the leaf. In September, 1915, 
several colonies of over 200 wingless individuals were observed on 
single blades of Typha at Walnut Creek, and about the end of this 
month the aphids reached their maximum abundance. This latter 
condition was repeated in 1916, although the colonies were never as 
