[ 304 J 



XXV. 



BIOLOGICAL STUDIES OF APHIS RUMICIS L. 

 A.— Appeakance of WinCxED Forms. 

 B.— Appearance of Sexual Forms. 



By J. DAVIDSON, D.Sc. 



From the Entomological Department, Institute of Plant Pathology, 



Eothamsted Experimental Station, Harpenden, Herts. 



(communicated by professor g. h. carpenter.) 



[Read April 26. Published August 29, 1921.] 



CONTENTS. 



PAGE 



Introduction and Experimental Data. 



(a) Fundatiix generation on Euonymus, 305 



(b) The First viviparous generation on 



Euonymus, .... 305 



(c) Successive viviparous generations on 



Euonymus, . . . 305 



(d) Successive viviparous generations on 



Rumex, .... 307 



(e) Successive viviparous generations on 



Beans, . . . • 



(f) Euonymus infected from Beans, 



II. General Discussion. 



(A) Appearance of winged forms, 



(B) Appearance of sexual forms, 



III. Summary, . ... 



IV. References, 



P AG li 



308 

 309 



310 

 315 



321 

 322 



I. — Introduction and Experimental Data. 



The results embodied in this paper have been derived from extensive 

 breeding experiments with this species in captivity during 1913-14 in 

 Germany and 1920 at Eothamsted. Ova were found on March 25th, 1914, 

 and were hatched out in the laboratory, the Fundatrices being transferred to 

 small Euonymtis bushes, Rumex plants, etc., which were grown in pots, and 

 kept covered with muslin bags. As each succeeding generation became 

 adult, some of the offspring were transferred to new plants. In this way the 

 history of the aphids used was known, and the exact generation with which 

 the various plants were infected. LTnfortunately, for the 1920 experiments, 

 ova could not be found, so that the colonies in these experiments were 

 started from an early, viviparous, parthenogenetie generation found on 

 Euonymus europaeus on the Eothamsted farm on May 10th, 1920. 



The plants were grown in 10" pots in a large open glass-house in summer, 

 and a warm green-house in winter. The daily maximum and minimum 

 temperature of the green-house throughout the winter is shown in fig. 2. 



