12 BULLETIN 774, TJ. S. DEPARTMENT OF AGRICULTURE. 



large as the year previous. As has been noted, the aphids lie parallel 

 to the length of the blade. They move off at slight disturbance and 

 much difficulty was experienced in transferring individuals, owing to 

 their failure to settle on a new plant. 



Toward the end of October the blades frequently turn yellow, 

 causing the aphids resident thereon to assume a straw-colored ap- 

 pearance. 



The aphids frequently deposit a little circle of "meal" around 

 them on the surface of the blade, a habit similar to that practiced on 

 the same host by a species of white fly. On leaves of Phragmites the 

 aphids congregate in large masses on both surfaces, lying parallel to 

 the long axis of the leaf. The central portion of the leaf is colonized 

 first and as the colony increases in numbers the infested area ap- 

 proaches the margins. 



THE FALL FORMS. 



There are three fall forms — the fall viviparous migrant, the male, 

 and the sexual oviparous female. The first two fly to the winter 

 hosts, after which the viviparous migrants deposit the sexual ovipar- 

 ous females. 



FALL MIGRANT. 



Description. 



The immature stages do not differ materially from those of the spring mi- 

 grant. 



The adult insect, aside from being slightly smaller and having the antennae, 

 legs, and style more dusky, is similar to the spring migrant. Form elongate. 



Antennae on somewhat gibbous frontal turbercles, about two-thirds as long as 

 the body. Comparative measurements as follows : I, 0.07 mm. ; II, 0.06 ; III, 

 0.39; IT, 0.235; Y, 0.175; VI, 0.48 (0.10 plus 0.38). Beak reaching a little be- 

 yond anterior border of mesosternum, 0.26 mm. in length. Wings 2.6 mm. in 

 length. Cornicles shaped as in spring migrant, 0.075 mm. long. Style ensiform, 

 0.16 mm. long. 



Sensoriation and tubercles as in spring migrants. 



REPEODUeTIOX AND HABITS. 



The migrants normally locate on the underside of the leaves (of the 

 winter host), but those that arrive latest in the season often find the 

 leaves blown off by winds and perforce settle on the twigs. Fre- 

 quently they feed for several days before producing young. In ex- 

 perimental cages inclosing Agen {French) prunes and Myrobalan 

 plums 14 was the highest number of young laid by a single migrant, 

 and the average was about 8 (excluding about 20 per cent of the indi- 

 viduals which died without bearing progeny). The migrants were 

 more prolific on Agen {French) prunes than on Myrobalan plums. 

 In the field it appeared that from 12 to 35 young sexual females are 

 produced normally, with an average of about 20, on French prunes. 



