103 Psyche [June 



temperatures. In spite of the precautions observed in the present 

 experiments, at about the end of October and the first week of 

 November, 1920, when the tansy plants were still in apparent!}' 

 good condition, the aphids produced amphigonous individuals and 

 laid winter eggs, in the same manner as the insects of identical 

 species which were exposed to the more adverse weather conditions 

 in their natural environment outdoors. 



In the same greenhouse were a number of plants of Nicotiana 

 alata Otto et Fink. These had been observed by me since Sep- 

 tember, 1919, to be infested with Myzus persicce Sulzer. The 

 insects, which are a common greenhouse pest in this part of the 

 country, were probably descendants of parents that had been asso- 

 ciated with greenhouse plants for a long period of time, and thus 

 had been continually protected for generations from the drastic 

 effects of winter. These individuals of Myzus fersicce in the green- 

 house, which were under the influence of the same temprature con- 

 ditions as the tansy aphids, continuously reproduced parthenoge- 

 netically throughout the winter of 1919-1920 and of 1920-1921. , 



At the time the above experiments were conducted, there was no 

 facility available for a more accurate regulation of temperature 

 and other conditions. The simultaneous presence in the same place 

 of parthenogenetic forms of Myzus persicce, however, tends to 

 eliminate to some extent the possibility of adverse conditions exist- 

 ing in the greenhouse and bringing about amphigony in Macro- 

 siphum tanaceti. Another difficulty in the present experiments 

 was that I had no opportunity to work with material of identical 

 species for control. However, under natural conditions outdoors 

 in this locality, both Myzus persicce and Macrosiphum tanaceti be- 

 gin to produce winter eggs at about the same time of the year, in 

 the fall. 



In apparent contradiction to my findings on Macrosiphum tana- 

 ceti are the results reported by Slingerland (1893) in his work on 

 Myzus achyrantes Monell, which species is considered by Gillette 

 and Taylor (1908) as a synonym of M. persicce. On April 2, 

 1890, Slingerland isolated the nymph of a wingless, partheno- 

 genetic female, and within two years and ten months from that 

 date he succeeded in raising from his material sixty-two succes- 

 sive generations of parthenogenetic individuals. The work was done 



