434 Journal of Agricultural Research voi. xv. No. s 



females confined with males in large sterilizing tubes have been observed 

 in copulation as many as four to seven times during a given hour. Mating 

 is probably best secured with the parasites confined in large screened cages 

 a foot or more in diameter. Large cages with plenty of light are cer- 

 tainly superior to glass tubes for this purpose, although mating will 

 occur in small shell vials. Under certain conditions males of Dia- 

 chasma tryoni have mated with females of D. fiillawayi. This may 

 be brought about by confining many fresh males of tryoni with a few 

 females of both tryoni and fullaivayi. The progeny from two fullawayi 

 females mated in this manner on June 29, 191 6, were all males. Evi- 

 dently these two species can not be crossed. 



Males are more abundant than are females. During 191 6 and 191 7, 

 16,845 males and 10,130 females were bred from fruit-fly material col- 

 lected in the field. Experiments conducted in the laboratory show 

 that mated females produce a varying proportion of male and female 

 progeny. From 1 1 mated females emerging on July 6 and 7 and August 

 24, 1 91 7, and immediately isolated into separate cages for oviposition 

 until death, the following progeny were secured: No. i, 13 males and 23 

 females; No. 2, 24 males andy females; No. 3, 19 males and 27 females; 

 No. 4, 5 males and 9 females; No. 5, 7 males and 21 females; No. 6, 14 

 males and no females; No. 7, 4 males and no females; No. 8, 49 males 

 and 10 females; No. 9, 16 males and 15 females; No. 10, 23 males and no 

 females; No. 11, 15 males and 2 females. In another case 25 freshly 

 emerged females were placed separately with males on July 13, 191 7, 

 and left until all had mated. From these a total of 189 males and 86 

 females was reared. Three females, known to have mated with vigorous 

 males four, five, and seven times, respectively, were given opportunity 

 to oviposit from August 9, 191 7, until death from three to four weeks 

 later. From these a total of 47 males and 24 females was reared. The 

 female which had mated seven times produced 14 males and 4 females. 

 Such data indicate the importance of other factors than mere successful 

 mating in the determination of sex proportion. 



Unmated females of Diachasma tryoni as well as the other two opiine 

 species treated herein are positively arrhenotokous. Ovipositing virgins 

 during 191 6 selected to prove this point consistently produced nothing 

 but males. 



Females may begin oviposition on the day of emergence, irrespective 

 of whether they have mated or not. The ovaries are well filled with 

 eggs, in a mature condition, at the time of emergence. Eggs are also 

 present in varying degrees of development (fig. 19). A dissection of the 

 ovaries of 24 females 24 hours old gave an average of 84 mature eggs 

 per female. The greatest number of mature eggs found in a single day- 

 old female was 125. Females which have been hibernating in the larva 

 stage from 3 to 12 months are fertile, mate and reproduce, but are not 



