346 



The Journal of Heredity 



broods. He does not give the numbers 

 of individuals for any of these broods. 



In commenting upon the data re- 

 corded by Bugnion for Ageniaspis, 

 Marchal points out that it is difficult 

 to account for the four broods in which 

 a large majority of individuals belong 

 to the one or the other sex. He believes 

 that such broods must arise from two 

 (or more) eggs. He further believes 

 that should two eggs, one fertilized and 

 the other not, be laid in the egg of the 

 host at slightly different times, the one 

 first deposited might gain the upper 

 hand in the matter of food, and thus 

 prevent all but a few of the individuals 

 arising from the second parasitic egg 

 from reaching maturity. 



During the past few years I have 

 been able to study in detail the poly- 

 embryonic broods of three distinct spe- 

 cies of parasitic hymenoptera. The first 

 species studied was Copidosoma gelc- 

 chiae, which is found in the larvae of 

 the Solidago gall moth, Gnorimoschcma 

 salinaris. This moth makes the ellip- 

 soidal galls on the stem of the marsh 

 goldenrod, Solidago senipcrvirens. The 

 second species investigated was Para- 

 copidosomopsis fioridanus, which lays 

 its egg in the egg of the common cab- 

 bage looper, Antographra brassicae. 

 Recently I have studied the broods of 

 Platygaster sp.,^ which is found in the 

 larvae of two dipterous gall-makers of 

 the mountain cedar (Sabina sabinoidcs). 

 The two hosts are JValshomyia texana 

 and Rhopalomyia sabinae. We shall 

 present the data on the sexes of these 

 three species in the order named. 



SEX RATIOS IN COPIDOSOMA 



A total of one hundred and sixty-two 

 broods of this species have been reared 

 and the sexes noted. Ninety of these 

 were female broods, sixty-two male, and 

 ten mixed. I shall here give only the 

 summary of these data, since the de- 

 tails have been published elsewhere 

 (Patterson, T5). On the per cent basis 

 these data show that 55.56% of all 

 broods are female, 38.27% male, and 



2 I am indebted to Dr. C. T. Brues, who kindly informs me that this species belongs to- 

 the genus Platygaster. I am also indebted to Dr. E. P. Felt for naming and describing the 

 two hosts here referred to. 



6.17% mixed. The total number of 

 individuals is 31,001, of which 63.41% 

 are females and 36.59% males. The 

 average number of individuals in fe- 

 male broods (198) is higher than in 

 male broods (175). However, the 

 range in the number of individuals in 

 the several broods (from 25 to 395 in 

 the female, and from 41- to 345 in the 

 male) is such as to indicate that the 

 average per brood is of little significance 

 in determining the true sex ratio for 

 the species. Obviously this must be 

 based on the number of male and fe- 

 male polyembryonic broods. It would 

 be easy to determine this ratio were it 

 not for the uncertainty of the origin 

 of some broods. If it be assumed, as 

 all previous investigators have done, 

 that each mixed brood is at least dizy- 

 gotic, then, in accordance with the law 

 of probability, some unmixed broods 

 must also be of dual origin. Worked 

 out on this basis, it is found that the 

 ratio of females to males is 106 to 76, 

 or a sex ratio of approximately 3 :2. 



The interesting point brought out in 

 the study of these insects is the ratiO' 

 of males to females in the ten mixed 

 broods. These are listed in the fol- 

 lowing table : 



Table I. — Mixed Broods of Copidosoma. 



Brood 



No. of 

 individuals 



Females 



Males 



* An incomplete brood, owing to the fact 

 that some of the larvae and pupae had been 

 destroj'^ed by a dipterous -larva. 



In each of the nine complete lots 

 listed in the table the number of fe- 

 males is greater than the number of 



