442 



Journal of Agricultural Research 



Vol. XV, No. 8 



The pupa may be distinguished from the pupa of Diachasma tryoni by 

 the short antennae and ovipositor sheath. The ovipositor sheath extends 



beneath the body and up over the abdomen but 

 the tips do not reach as far forward as the tho- 

 rax. The pupa stage is sHghtly shorter than is 

 that of D. tryoni. 



Although the egg, lar\^a, and pupa stages are 

 slightly shorter than are those of D. tryoni, the 

 average period covering their combined devel- 

 opment is consistently shorter by 3t 04 days 

 (Table III). During the summer months this 

 combined period averages 15^ days and in- 

 creases to about 20K days in the winter. As 

 eggs are deposited by the female on the day of 

 emergence, the life cycle of this species covers 

 a distinctly shorter average period than does 

 that of its host. 



ADULT 



The emergence of the adult is similar to that of 

 Diachasma tryoni. Males likewise precede the 

 females by a day or more. The meconium is 

 immediately discharged, as in D. tryoni. The 

 pupal skin is extremely thin and difficult to see. 

 The general habits of mating are identical with 

 those of D. tryoni. The male emits a distinct 

 but rather delicate sweet odor. No odor can be 

 detected on the female . The p roportion of sexes 

 is better equalized than is the case with D. tryoni. 

 During 191 6 and 191 7 a total of 6,128 males and 

 4,715 females was reared from material collected in the field. This is a 

 percentage of 56.5 of males as compared with a percentage of 62.4 of 

 males of D. tryoni secured over the same 

 period. 



In confinement no conditions could be 

 obtained under which this species would 

 reproduce as favorable a proportion of 

 the sexes as occurs in the field. The best 

 results were obtained with females con- 

 fined in a large glass jar (9 by 15 inches). 

 In one experiment 25 males and 25 fe- 

 males were placed in such a jar imme- 

 diately upon emergence, kept in strong light, and daily given material 

 in which to oviposit. In three days' time mating and oviposition oc- 



Fig. 24. — Opius humilis: Molted 

 skin of first-instar larva, showing 

 head characters. Length i mm. 



Fig. 25. — Opius humilis: Mandible of mature 

 larva. Length 0.065 nun. 



