THE POLYEMBRYONIC DEVELOPMENT OF PLATYGASTER 
VERNALIS 1 - 
By R. W. Leiby, Assistant Entomologist , North Carolina Agricultural Experiment 
Station , and C. C. Hill, Assistant Entomologist , Cereal and Forage Insect 
Investigations , Bureau of Entomology , United States Department of Agriculture 2 
INTRODUCTION 
In a previous paper the writers (4) 3 referred to the desirability of demon¬ 
strating insect polyembryony in a species in which but a few individuals are 
developed from a single egg. The development of such a species was in part 
described for Platygaster hiemalis , a parasite of the Hessian fly. 4 It was found, 
however, that polyembryony was carried only to the point where twin parasites 
were produced from a single egg, thus demonstrating the simplest type of poly¬ 
embryony possible. 
A slightly more complex form of polyembryony will be described here for 
Platygaster vernalis (Myers), another parasite of the Hessian fly, in which an 
average of about eight individuals are developed from a single egg of the para¬ 
site. A knowledge of the development of this species will furnish a further 
clue to the more highly specialized forms of polyembryony in which as many 
as 150 to 2,000 individuals are produced from a single egg. 
Platygaster vernalis develops only in the mid-intestine of the host larva. The 
development of a closely related species, Polygnotus minutus Lindemann, which 
is also confined to the mid-intestine of the Hessian fly larva in France, has been 
described previously by Marchal ( 5 ). Marchal’s paper upon this insect is now 
difficult to obtain. However, his paper does not treat of the precleavage or 
cleavage stages of development in a sufficiently detailed manner to demonstrate 
polyembryony, but it does describe quite fully the organogeny of the embryos. 
There are also some indications that P. minutus and P. vernalis differ slightly 
in the details of their development, although it is difficult to determine this 
definitely, because the development of Marchal’s species is not illustrated with 
sufficient histological preparations. In the present paper, therefore, emphasis 
has been placed upon a study of microtomic sections, and the paper has been 
illustrated 5 from this viewpoint rather than upon gross examinations. 
RELATION OF PARASITE TO HOST 
The biology of P. vernalis with particular reference to its economic importance 
as a parasite of the Hessian fly, which is a serious pest of wheat, has been pre¬ 
viously dealt with by the junior writer (2). The adults emerge from their 
1 Received for publication April 22, 1924. 
2 The writers gladly acknowledge the continued interest shown by Dr. L. 0. Howard and W. R. Wal¬ 
ton in the studies reported in this paper. To Doctor Howard is due the chief credit for calling the atten¬ 
tion of American investigators to insect polyembryony. Our studies on the development of the Platygaster 
parasites of the Hessian fly were initiated at the direction of Mr. Walton. 
3 Reference is made by number (italic) to “Literature cited,” p. 839. 
* Phytophaga destructor Say. 
5 All of the illustrations of microtomic sections except figures C and D on Plate 1 were drawn by the 
senior writer. The remainder of the drawings were prepared by the junior writer. The photomicro - 
graphs were made by the photographer of the Bureau of Entomology. 
Journal of Agricultural Research, Vol. XXVIII, No. 8 
Washington, D. C. May 24, 1924 
Key No. K-130 
( 829 ) 
96038—241-10 
