81 



BIOLOGICAL STUDIES OF APHIS RUMICIS, LINN.* 



By J. Davidson, D.Sc. 

 The Entomological Department, Institute of Plant Pathology, 

 Rothamsted Experimental Station, Harpenden. 



This is the iirst of a series of papers based on resulLs of breeding experiments and 

 on observations in the field. It is hoped that a full investigation of the biology of this 

 species will be of value in elucidating the many difficult biological problems of the 



APHIDIDAE. 



The preliminary paper published by the author (1914) was to have been followed by 

 further investigations, but owing to the outbreak of the European War there has 

 been an unavoidable delay. However, experiments are now being continued, and the 

 results of the researches will be published in parts from time to time. 



As there is no complete description of Aphis rnmicis in the hterature, it is thought 

 very desirable that a detailed illustrated description of all forms of this species should 

 be given. 



The following abbreviations are used in the text : — a.v. $ = apterous viviparous 

 female ; w.v. $ = winged viviparous female ; 1st v. gen. = 1st, 2nd, etc., viviparous 

 generation. 



I. Description of Aphis rumicis, Linn. 



1. FuNDATRix (fig. 1). Average size, 1 -8 mm. by 1 -4 mm.t 



Body oval to elongate, broadly rounded posteriorly, shorter and relatively stouter 

 than the succeeding a.v. $ $ ; colour black to dark green ; hairs scattered over 

 the body. 



Head : A few scattered hairs on dorsal surface. Eyes black ; small tubercle-like 

 accessory eyes| on posterior margin. Antennae§ about two-thirds length of body ; 

 black to dark brown, paler about the middle ; five segments ; seg. 3 the longest ; 

 1 slightly broader than long ; 2 slightly longer than broad, subequal in length ; 

 4 shorter than 5 ; 5 almost as long as 3 ; a single subapical sensorium on seg. 4 and 

 a compound sensorium on seg. 5 ; a few short hairs on each segment. Rostrum 

 normal, with a few hairs on each segment. 



Thorax : A pair of prominent lateral tubercles on prothorax. Legs black, with 

 tibiae and proximal portions of femora paler ; segments bearing many short hairs, 

 especially the tibiae. 



Abdomen with two prominent lateral tubercles on each side. Cornicles black to dark 

 brown, imbricated, tubular, tapering very slightly distally, shorter than in succeeding 

 a.v. $ $ ; about one and one-third times the length of cauda as seen from the dorsum. 

 Cauda short, bluntly rounded, black on distal portion ; bearing several long curved 

 hairs. Anal plate black, roughly quadrangular as seen from venter, bearing a 

 number of short hairs, anterior margin more or less straight. Genital plate black, 

 somewhat crescentic in shape, with outer margins rounded ; bearing a number of stout 

 hairs and short spines. 



* This species is the black aphis found in spring on the spindle tree [Euonymus europaetis), 

 and later on beans, poppies, and manj^ other plants. It has many synonyms, owing to its poly- 

 phagous habits, but the name given by Linnaeus in 1746 holds priority. The more important 

 synonyms are Aphis papaveris, Fabr. ; Aphis euonymi, Fabr. ; and Aphis fabae, Scop. For other 

 synonyms see Theobald, 1912. 



t The measurements given are total length of body excluding the cauda, and the greatest width 

 of the abdomen. The size is very variable, depending largely on food and temperature conditions. 



X Accessory eyes (Berlese, " Gli Insetti ") ; ocular tubercles (Baker, 1920). 



§ The "unguis" (Baker, 1920), or "processus terminalis " (Tullgren, 1909), of the terminal 

 segment is here considered as being part of the distal segment. 



(2416) F 



