51 



BIOLOGICAL STUDIES OF APHIS IWMICIS 

 LINN. 1746.1 



By J. DAVIDSON, D.Sc. 



{From the Entomological Dejiartment, Institute of Plant Pathology, 

 Rothamsted Experimental Station, Harpenden.) 



(With 1 Text-figure.) 



Introduction. 



In a previous paper (2), the author raised the question as to the 

 influence of the different host plants on the reproductive capacity 

 of Afliis rumicis and the resulting varying degree of infestation of 

 different plants. From observations made on certain intermediate hosts 

 of A. rumicis, it was found that some species of plants were more heavily 

 infested than others, and an attempt has been made in the following 

 experiments to obtain a numerical expression of the infestation of plants 

 and of the relative susceptibihty of the various hosts. 



Experiments were carried out during 1913-14 at the Kaiserhche 

 Biologische Anstalt fiir Land und Forstwirtschaft, Berhn, but owing to 

 the war this series of experiments was terminated in July 1914 and, 

 \\ath the absence of the writer on service, it was not found possible to 

 continue the work until the year 1920. 



Some of the 1914 results (series A and B) are now given, together 

 with certain of those for the season 1920 (series C and D). 



In the 1914 experiments the aphids used were raised from ova. 

 Ova of Aphis rumicis were found on Euonymus europaeus near Berhn, 

 on March 25, 1914. These ova hatched out in the laboratory and the 

 larvae of the Fundatrices were reared on Euonymus twigs grown under 

 bell jars in wet sand. Some were then transferred to young Euonymus 

 europaeus bushes grown in pots. The aphids used throughout the experi- 

 ments were thus reared in captivity from the ova, through successive 

 viviparous parthenogenetic generations as described below. Thus the 



1 A grant in aid of publication has been received for this communication. 



4—2 



