268 FRANZ SCHRADER 
The only doubt which may exist arises from the question 
whether the same species is concerned in both countries. In 
this connection, A. C. Baker, of the U. 8. Bureau of Entomology, 
having gone over some of Williams’ English specimens, assures 
me that they are morphologically indistinguishable from the 
species occurring in America. We are therefore concerned with 
two lines of a species, which differ in their parthenogenetic 
behavior. 
That these lines or races are not strictly confined within definite 
geographical limits may be indicated by an exceptional occur- 
rence at Merton, England, where Williams found that over 34 
per cent of 287 specimens were males. He believes, however, 
that they may have been introduced with some recently acquired 
plants. Unfortunately, all the families raised from virgin fe- 
males of these exceptional white flies died before their sex could 
be determined, and no subsequent breeding experiments were 
made. I have not found the converse case to this in my work 
here, but think it perfectly possible that an occasional strain of 
parthenogenetic female producers may exist. 
Very few observations have been reported on the offspring of 
mated females. Williams succeeded in raising two very small 
broods from mated females which came from the exceptional 
Merton strain. In these broods, as in broods which I have raised 
from mated American females, both sexes were represented. Mr. 
Williams informs me that he never observed copulation in speci- 
mens of the ordinary English stock. The broods produced by 
females used in such experiments were always exclusively female, 
but, since it is questionable whether fertilization had taken place, 
no conclusions can be reached from such data. 
Summed up, we thus have the following: 
1. Trialeurodes vaporariorum has two races, one of which gives 
rise by parthenogenesis to males (America), the other to females 
(England). 
2. Mated females of the male producing race give rise to both 
SEXES. , 
The present work has been confined to the race occurring in 
America. I am indebted to Prof. E. B. Wilson and Dr. A. H. 
Sturtevant for aid and encouragement. 
