36 
Journal of Agricultural Research 
Vol. XXV, No. X 
In this diagram 12 Hessian fly eggs are represented in approximately 
the same position as they occurred on the wheat leaf. A vernalis female 
was allowed to visit these eggs twice. During the first visit the eggs 
marked with a cross were attacked. The dotted line plots out the 
course of the second visit, and the circles indicate the eggs attacked 
during this trip. During the second trip the female examined each of 
the eggs with the exception of the one at the extreme end, but she con¬ 
sistently refused to oviposit in any except two which had been omitted 
during the first trip. 
Experiments indicate that Platygaster vernalis lays only one egg 
during a single oviposition. This is the usual number found in reared 
material and in that collected in the field. In confirmation of this 
belief, it was found that 11 host eggs laid in confinement and dissected 
immediately after having been punctured by this species contained but 
one vernalis egg each. 
potential progenitiveness 
At the time of eclosion of the adults the eggs have reached their full 
development in size. In order to ascertain the average number of eggs 
contained in the ovaries, the eggs of 10 females were dissected out and 
counted. The count showed an average of 228.3 eggs per female, with 
a maximum of 290 and a minimum of 117. The eggs are so small and 
numerous that in order to count them it was necessary to spread them 
out in a liquid on an eye-piece micrometer disk ruled into 1 millimeter 
squares. By counting the eggs from one ovary at a time, accurate 
results were possible. 
length of life 
In order to obtain data on the length of life of the adult, 59 adults 
were divided into three groups subject to different conditions. Lot 1 
included 15 females and 4 males, placed in a large dry vial plugged with 
cotton and with a little sugar solution for nourishment. Lot 2 contained 
14 females and 8 males in small vials plugged with cotton and left in a 
saturated atmosphere, with water accessible. Lot 3 consisted of 15 
females and 3 males in small vials in a saturated atmosphere but with 
sugar solution for nourishment. The atmosphere for Lots 2 and 3 was 
kept saturated by placing the vials in a relaxing box. The results are 
summarized in Table II. The shortest length of life was 3 days and the 
longest 27 days; in Lots 1 and 2 the average length of life of the females 
exceeded that of the males; and the parasites left in a saturated atmos¬ 
phere with water available had the longest average length of life, namely, 
12.21 days. Throughout the experiment the temperature of the labora¬ 
tory in which it was conducted varied from 45 0 F. to 78° F., with an 
average temperature of 61 0 F. 
Extremely low or high temperatures undoubtedly have some effect on 
the length of life. Several adults, however, were subjected to a tem¬ 
perature of 24 0 F. ( — 4.45° C.) for a period of 5 hours without any 
noticeable ill effects. Adults subjected to heat expired within a minute 
at temperatures from 117.68° F. to 120.2° F. (47.6° C. to 49° C.). Short 
exposures to temperatures of 117.22° F., 116.60° F., and lower did not 
prove fatal. 
