346 
Journal of Agricultural Research 
Vol. XXV, No. 8 
Platygaster, which emerge in relatively small numbers from an individual 
host specimen. For example, on an average 6.31 adults of P. hiemalis 
issue from a single host carcass; and the mixed broods frequently show 
a sex ratio such as five females and one male, or seven females and three 
males. The rearings of 100 parasitized puparia show that 20 contained 
no males (pure female broods); and of the 80 mixed broods 23 contained 
one male, 25 contained two males, 12 contained three males, and 20 
contained four or more males. In 71 of the 100 puparia the females ex¬ 
ceeded the males in number, in 24 the males exceeded the females, while 
from the other five host puparia the males and females were reared in 
equal numbers. Unpublished studies on Platygaster sp. are available in 
notes of the senior writer which show a similar sex ratio. 
Patterson (6, 7) has also pointed out the sex ratio of Platygaster felti 
Fouts, but in this species the average number of parasites (15 per brood) 
issuing from a single carcass is nearly three times as great as in P. hiemalis . 
P. felti oviposits one or two eggs in a single host egg and not from six to 
eight, as does P, hiemalis. The probabilities are that felti develops more 
than two parasites from a single egg, thus carrying the polyembryonic 
method of development beyond the twinning stage. 
With reference to the development of mixed broods in Platygaster felti , 
Patterson has proposed the theory that both sexes arise from a single egg. 
He believes that the most probable way that this will be found to occur 
is by the Bridges method of somatic nondisjunction of the sex chromosome 
during cleavage of the embryonic nuclei. 
The writers believe that the mixed broods of Platygaster hiemalis can 
be readily accounted for by the fact that both fertilized and unfertilized 
eggs are deposited in the host at the same time, 8 a condition which has 
been shown to occur regularly. The writers do not believe that this 
parasite controls insemination as the honeybee apparently does, but the 
short period of time required by the parasite to deposit a group of from 
six to eight eggs indicates the probability of the eggs passing the sperma- 
theca duct so rapidly during oviposition that all of the eggs do not receive 
a sperm. 
The writers believe also that the monembryonic development of some 
of the eggs of a group deposited by Platygaster hiemalis will account for 
the production of single males, or males in small numbers, in a mixed 
brood where females predominate, and similarly for single females or 
females in small numbers in a mixed brood where males predominate. 
In P, hiemalis the mixed broods more commonly yield a preponderance 
of females. To take a case in point, a common number of parasites 
reared in a mixed brood is 8, with a sex ratio of 6 females and 2 males. 
Studies of the number of eggs deposited by females in groups at the 
same time permit the writers to assume that in this instance 7 eggs 
were deposited in this group. Of the 7 it is also fair to assume that 4 
were inseminated and 3 were not inseminated. If 2 of the 7 eggs became 
aborted in the course of development, and these 2 represented a fertilized 
and an unfertilized egg, there would remain 3 fertilized and 2 unfertilized 
eggs to develop successfully. The 6 females and 2 males of the mixed 
brood taken as an example would therefore have been produced by the 
twinning of each of the 3 fertilized eggs and the monembryonic develop- 
9 This fact can be readily ascertained with accuracy by examining the eggs of a group deposited by the 
parasite. All the eggs of such a group are identically fixed and stained, and their smallness of size per¬ 
mits several eggs of the group to be contained side by side within a single section cut 6m thick. Under 
these conditions some of the eggs of a group show a sperm within while others show no sperm. 
