July 7,1923 
Platygaster vernalis, Hessian Fly Parasite 
37 
Table) II. — Length of life of Platygaster vernalis adults 
[Lot 1 was kept in a dry atmosphere with sugar solution for nourishment; Lot 2 in a saturated atmosphere* 
with water; and Lot 3. in a saturated atmosphere, with sugar solution for nourishment] 
Number of adults. 
Length of life in days. 
Lot. 
Female. 
Male. 
Maximum. 
Minimum. 
Average. 
Female. 
Male. 
Total. 
I 
15 
4 
6 
3 
4-53 
3 
4.15 
2 
14 
8 
26.33 
3 
14.7 1 
9.61 
12.21 
3 
15 
3 
27 
3 
8.46 
8.89 
8-53 
OTHER BEHAVIOR 
When in confinement the adults crawled rapidly about but very seldom 
flew. They nearly always moved toward the light. When suddenly 
disturbed, they feigned death by drawing up the legs and antennae close* 
to the body and remaining in this attitude for a few seconds. In actual 
death, the antennae and legs are found stretched away from the body. 
When at rest, the body is usually held in a crouched position, but with 
legs and antennae not drawn as close to the body as when simulating 
death. 
For nourishment the adults readily take up sugar solution. When 
allowed to go a few days without water, they became very thirsty, as 
was demonstrated by the quickness with which they found a drop of 
water placed near them and the eagerness with which they accepted it. 
When emerging, the adult parasite gnaws a round or irregularly 
shaped exit hole through the cocoon and puparium. (PI. 3, F.) Some¬ 
times a few such holes in the host puparium are sufficient to permit 
all the adults within the host to escape. 
SEASONAL HISTORY 
To obtain data on the duration of the various stages of Platygaster 
vernalis under normal field conditions, dissections were made of the 
Hessian fly in various stages collected at intervals throughout the year. 
Such records were kept during 1918 at Carlisle, Pa., 1919 and 1920 at 
Mount Holly Springs, Pa.; and 1921 at New Windsor, Md. 
The lines on figure 2 show the maximum range of occurrence of each 
stage as determined by the earliest and latest records of their presence 
in the field, assembled from data collected during the four years men¬ 
tioned. The records of the occurrence of adults were obtained by sweep¬ 
ing, and those of the embryos from dissections of Hessian fly larvae after 
they had descended to the bases of the plants. Since Platygaster vernalis 
oviposits in the egg of its host, embryos of this parasite must have 
occurred in the field somewhat earlier than is indicated in the figure. It 
may be observed that the vernalis larvae spend considerable time within 
cocoons before pupating. Cage rearings, checked by field examinations 
made during the winter, show that the adults normally remain within 
the cocoons until early spring. The line representing this stage on the 
chart has not been extended farther than to September 27 for economy 
