Vol. XXXII. May, 1917. No. 5. 



BIOLOGICAL BULLETIN 



STUDIES ON THE BIOLOGY OF 

 PARACOPIDOSOMOPSIS. 



I., DATA ON THE SEXES. 1 



J. T. PATTERSON. 



I. INTRODUCTION. 



According to Marchal ('04) and Silvestri ('06, '08) sex-deter- 

 mination in the polyembryonic chalcids is brought about in the 

 same manner as in the bee. It is well known that the fertilized 

 egg of the bee produces a female (queen or worker), while the 

 unfertilized egg gives rise to a male (drone). Marchal and 

 Silvestri believe that the fertilized egg of these parasitic hymenop- 

 tera produces a polyembryonic brood of females, while the un- 

 fertilized egg develops into a brood of males. This conclusion 

 has been widely accepted, not only because it is in harmony 

 with the Dzierzon theory of sex-determination in the bee, but 

 also because several different investigators have observed that a 

 polyembryonic brood usually does not contain individuals of 

 both sexes. The occasional appearance of a mixed brood has 

 been explained by the obvious and apparently logical assumption 

 that a fertilized and an unfertilized egg had been deposited in a 

 single egg of the host. The simultaneous development of two 

 such eggs would naturally produce a mixed brood of parasites. 



In a recent paper dealing with the development of the poly- 

 embryonic chalcid, Copidosoma gelechicz, the writer ('15) called 

 attention to the fact that it was difficult to explain the origin 

 of certain mixed broods of this species on the assumption that 

 two parasitic eggs carrying the opposite sex factors had been 



1 Contributions from the Zoological Laboratory of the University of Texas, 

 No. 130. 



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