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. 



Newly hatched. — Similar to that of spring wingless form, but more yellowish. 

 Form elongate. 



Adult. — In color similar to those of spring wingless, but smaller in size and 

 narrower in shape. 



Antennae about two-thirds body length. Comparative measurements as fol- 

 lows : I, 0.08 mm.; II, 0.045; III, 0.26; IV, 0.1G ; V, 0.155; VI, 0.40 (0.08 plus 

 0.32). Beak reaching second coxae, 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 



