HYMENOPTERA 



315 



distinctly crescentic in shape (Fig. 263A). Owing probably to an 



unfavorable location within the host, some parasite eggs fail to develop. 



Parasites continue their development from the blastula stage during 



the fall months (Fig. 263B), until in early winter they are in an advanced 



nu.p 



A B 



Fig. 263. — Platygaster. A, early blastula stage. B, later blastula stage, (am. 

 Trophamnion. {emb) Blastula stage of developing embryo, (host) Host tissue. {nu. 

 Paranuclear masses. 



emb 



embryo stage in which they exhibit larval characteristics (Fig. 264). 

 During this interval all the embryos that have arisen by the twinning 

 process become separated struc- 

 turally from each other, although 

 a twin pair may still be located 

 side by side. Each embryo is 

 found in an embryonic cavity, 

 the outer wall of which is the 

 trophamnion. During the devel- 

 opment of the embryo the tro- 

 phamnion is relatively thick and 

 contains many small or two large, 

 conspicuous paranuclear masses. 

 The parasites pass the winter as 

 well-formed embryos distributed 

 between the fat bodies of the host. 

 Meanwhile the host becomes fully 

 grown and encased in a puparium on the wheat plant. 



In the spring the parasites continue their development. The embryos 

 straighten out from their previous U-shaped form and are now recog- 

 nizable as young larvae. While this development is taking place, the 



Fit. 264 — Platygaster hiemalis. Embryo 

 {emb) within the trophamnion {flm. t) . 

 {nu. p) Paranuclear mass. 



