U. 'S. D. A., B. K. Tech. Ser. 112, Pt. VIII. Issued February 20, 1909. 



MISCELLANEOUS PAPERS. 



BIOLOGICAL STUDIES ON THREE SPECIES OF APHIDID.E. 



By John June Davis, 

 Of the University/ of Illinois, Urbana, III. 



INTRODUCTION. 



This paper deals principally with the biology of three of our com- 

 moner species of aphides, and includes descriptions of the ditferent 

 forms in all their various stages, as well as a complete bibliography 

 of these species. 



I have carried on these rearing experiments for the past two years 

 in the insectary of the State entomologist of Illinois, Dr. S. A. Forbes. 

 Practically all of the data here given, however, were obtained in 1906. 



I am especially under obligations to Doctor Forbes, under whose 

 direction I have made the experiments — those relating to Aphis 

 maidi-radicis while serving as his assistant; to Dr. J. W. Folsom,' 

 who has aided me on all parts of this paper, and to Prof. F. M. 

 Webster, who read the manuscript and made helpful suggestions. 



THE CORN ROOT-APHIS. 



(Aphis maidi-radicis Forbes.) 



GENERAL ACCOUNT. 



The corn root-aphis was first recognized by Benjamin Dann Walsh, 

 who found it, in 1862, at Rock Island, 111., where it was doing consid- 

 erable damage to a small field of corn. At that time it was supposed 

 by Mr. Walsh to be a root form of the common corn leaf-aphis 

 {Ap?tis maidis Fitch), which lives on the upper parts of the corn 

 plant, while the corn root-aphis, as the name Avould indicate, lives on 

 the roots. 



Dr. S. A. Forbes first began the study of this root-aphis in 1883, 

 and most of the facts noAv known relating to its life history, ecology, 



123 



