140 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 7 



membrane, but soon freed themselves and after wandering about on 

 the leaf for a moment or two started down the leaf stalk and continued 

 to the ground. This deposition of young upon Chjenopodium was ob- 

 served many times during the next two weeks and in every case the 

 young lice proceeded directly to the ground. 



On July 5, 250 plants of Chenopodium album were dug and their 

 roots carefully examined for Pemphigus hetce colonies. Plants were 

 examined on many parts of the college grounds, only one or two being 

 dug in each locality. Sixty-five plants were found to be infested with 

 colonies of Pemphigus hetce made up for the most part of very young 

 lice. They were on fine rootlets that lay close to the surface of the 

 ground and in most cases the ground was cracked so that they had easy 

 access to the roots if they descended from the leaves. On August 5, 

 a similar search was made and out of the same number of plants ex- 

 amined in the same localities, 151 colonies were found. 



This, together with the fact that Pemphigus hetce seldom becomes 

 abundant in the beetfields before the middle of July, has led -us to be- 

 lieve that the principal source of infestation is the summer migrants, 

 from the cotton wood galls. " 



Fifty migrants confined singly in glass tubes gave birth to a total of 

 480 young or 9.6 each. The greatest number produced by any one 

 individual was 19. Young born to these migrants were placed upon 

 sprouting sugar beet seed in germination cups; they began to feed im- 

 mediately upon the fine rootlets. Others were placed upon the roots 

 of the sugar beet plants growing in pots and in time developed, into 

 typical Pemphigus hetce colonies of wingless viviparous females. To 

 avoid any chances of error, the roots of beet plants used in the experi- 

 ments were dipped in "Black Leaf 40" and the soil used was carefully 

 examined to see that it contained no root lice other than the young of 

 the summer migrants. 



The summer migrants, while resembling the fall migrants in general 

 appearance, differ very materially in structure, a fact which seems to 

 have been overlooked by most American workers in writing up other 

 species in this group, but which has been especially noted by Tullgren, 

 a Swedish writer.^ The two principal differences in this species are 

 in the number of sensoria on the antennse and the absence or presence 

 of wax glands on the thorax. In the fall migrants the arrangement of 

 the larger sensoria is as follows: III 4-9; IV 2-3; V 0; VI 0. In the 



1 Aphidologische Studien Arkiv For Zoologi Band 5, Xo. 14. 



The manuscript for this paper was submitted for publication November 8, 1913. 

 In the December number of the Annals of the Entomological Society of America, 

 volume 6, number 4, page 488, Professor C. P. Gillette has called attention to the 

 marked difference which exists between the alate fundatrigenia and the alate sexupara 

 of Thecabius populimonilis Riley. 



