lycSJ Leafy Dimorph of ChaitopJwriis Negundinis 131 



The dimorph of C. negundinis is indistinguishable from that of 

 C. testudinatus as described and figured by Kessler. 



Here follow some of the details of the life history. Looking 

 for this dimorphic aphid June 12, 1907, I found it common on 

 both the upper and the lower surfaces of the leaves of box-elder 

 at Urbana, 111. At that time the winged and wingless normal 

 forms were also abundant. The following figures show the abun- 

 dance of the dimorph. June 15 the total number on the upper 

 surfaces of twenty leaves was 1988, and on the lower surfaces, 

 2088 — a total of 4076 individuals on the twenty leaves, or an 

 average of 203+ to each leaf. July 19, on ten leaves which were 

 only slightly infested and in a shaded situation, the total number 

 of individuals on the upper surfaces was 214, while on the lower 

 surfaces there were but 23 — a ratio of 9 on the upper to i on the 

 lower. After July i the normal forms began to disappear, and by 

 July 19 they occurred only occasionally. Between that date and 

 August 5 none of the normal forms were noticed, although careful 

 searches were made for them. August 5, however, I found four 

 young of the normal form and from one of these I obtained young. 

 She began to bear young August 13, and bore in all 73 young, of 

 which 27 were dimorphs and the remaining 46 normal forms. 

 Owing to my absence I was unable to trace these to the sexual 

 forms. August 20 I found the aphids becoming suddenly abun- 

 dant on the box-elder leaves. These aphids had a decidedly red- 

 dish tinge, and were, I infer, dimorphs which had molted; since 

 a dimorph that molted August 27 later developed into a reddish 

 normal form. Both out-of-doors and in the insectary I ha\'e 

 noticed the dimorphs in the act of molting. 



It is probable that the fully developed dimorphs are the 

 mothers of the sexual forms, although I have no positive evidence 

 of this. I infer, also, that the mothers of the dimorphs may be- 

 long to any of the earlier generations. 



The dimorph is capable of locomotion. In a chimney cage 

 containing a small box-elder plant I placed pieces of leaves bear- 

 ing dimorphs. As soon as the pieces of leaves began to dry up 

 the dimorphs moved from them to the fresh leaves. In another 

 instance the dimorphs, when transferred directly to fresh leaves 

 with a brush, attached themselves readily to these. 



I have found this dimorphic form in many localities in northern 

 and southern Illinois, but most abundantly at Urbana. 



* Read at the Chicago meeting, December .30th, lOOl 



