Davidson — Biological Studies of Aphis rumieis L. 311 



question further, however, 1 hope to sliow with reference to the results of my 

 experiments that those obtained by the latter authors are by no means 

 conclusive. 



Ewing, working with Aphis avenae Fab., considers temperature is the 

 determining factor. The optimum temperature of 65° F. resulted in only 

 apterous forms being produced during 20 parthenogenetic generations. 



Klodnitzki obtained winged forms along with apterous forms in most 

 generations when breeding the dark green and brown varieties of Sipliono- 

 pliora (Macrosiphum) rosae Koch, in normal and abnormally low temperatures. 

 Similarly with Aphis hederae Kalt., over 35 agamic generations, winged forms 

 appeared in low temperatures as in normal temperatures. There was a 

 tendency for a. v. ? ? to produce winged forms. 



Shinji investigated the iniluence of food conditions on the production of 

 winged forms in Aphids. By growing cut stems of plants infected with 

 aphids, in sand moistened with solutions of certain chemical substances, he 

 obtained results which suggest that the percentage of winged forms produced 

 was influenced. This was especially the case with solutions of Mg. sulphate. 



The figures obtained are interesting, but a further investigation of the 

 subject is desirable. It is necessary to know the history of the Aphids 

 experimented with, and the number of the viviparous generation used. 

 Comparisons between the effect on the offspring of w. v. ? ? and a. v. ? ? 

 respectively should be observed. The varying individuality of the Aphids 

 concerned, relative to an inherent tendency to wing development, should be 

 known. Temperature and humidity factors must also be considered. 



It will be seen in my experiments that winged forms appeared in most 

 of the generations. Winged viviparous females produced as a rule only 

 apterous viviparous females, although in one or two cases (see text, fig. 1) 

 a few winged forms developed as well as apterous forms. Apterous viviparous 

 females, offspring of w. v. ? ? , usually produced a varying percentage 

 of winged forms, although sometimes only a. v. ? ? were produced. This 

 sequence was the same on different species of plants. 



Winged forms have been obtained on young succulent shoots of 

 Euonymus europaeus and apterous forms on " woody," non-succulent plants. 



Pood conditions, therefore, would appear not to be the deciding factor. 

 The tendency appears to be for a. v. ? ? to produce a mixed progeny of 

 w. V. + + and a. v. + +, or in some cases only a. v. ° +. W. v. ° +, on the 

 other hand, invariably produce a. v. ? ? , with ouly occasionally winged forms 

 in later generations. It is seen that when a plant, either the winter host 

 (^Euo'nymus), or an intermediate host (Beans), is infected, either with 

 a. V. ? ? or w. V. ? ? , and the Aphids allowed to reproduce freely on the 



