1929 ] Thelytoky or Arrhenotoky in Sclerodermus 119 
THELYTOKY OR ARRHENOTOKY IN 
SCLERODERMUS IMMIGRANS 
By John Colburn Bridwell, 
Glencarlyn, Virginia. 
Parthenogenesis is a common occurence among hymen- 
optera. Usually it is androgenetic, only males being produced 
by virgin females. This phenomenon has also been termed 
arrhenotoky. It is so general among hymenoptera as to lead 
many students of the group to believe that all the species 
of the order may breed in this way except for the few 
which have developed thelytoky, virgin females producing 
females. Certain Eupelmidse and Encyrtidse among the 
Chalcidoidea, and some Ichneumonidse have been bred 
through many generations without males appearing and 
have to all appearances entirely eliminated sexual reproduc- 
tion as a part of ontogeny. In other instances however after 
long periods of gynogenetic parthenogenesis, small numbers 
of males appear and it is far from certain that any of the 
species have become perfectly thelytokous. I know of no 
species, however, which produce large numbers of males 
and also produce females parthenogenetically. The notes 
by Dr. Keeler, 1929 (Psyche 36:41-44) on thelytoky in 
Scleroderma immigrans are so much at variance with my 
experience in breeding Sclerodermus 1 that I am convinced 
an error of observation has mislead him. 
The discussion of the biology of Sclerodermus immig- 
rans Bridwell and its endemic Hawaiian congeners may be 
found in the Proceedings of the Hawaiian Entomological 
Society 4 :291-305, 1920. In the course of the work recorded 
several thousand individuals of this species were reared un- 
der very close and long continued observation and among 
them were many known virgin females whose progeny in 
every instance were males. In many instances the lots of 
1 It may not be superfluous to note again that Sclerodermus is La- 
treille’s original spelling of this generic name and Scleroderma a wholly 
unnecessary emendation on the part of Westwood. 
