PL AT Y G ASTER VERNALIS MYERS, AN IMPORTANT 
PARASITE OF THE HESSIAN FLY 1 
By Charles C. Hill 2 
Scientific Assistant, Cereal and Forage Insect Investigations, Bureau of Entomology, 
United States Department of Agriculture 
INTRODUCTION 
In the fall of 1914, W. R. McConnell and P. R. Myers undertook an 
exhaustive study of the Hessian fly (Phytophaga destructor Say) at 
Hagerstown, Md., with particular reference to its parasites. Since that 
time more or less consecutive records have been kept of the occurrence 
of one of these parasites, Platygaster vernalis Myers, 3 throughout the 
eastern wheat-growing region. In 1917 the laboratory at Hagerstown 
was transferred to Carlisle, Pa., and in this year the writer joined in the 
investigations. During the course of these studies P. vernalis was first 
recognized and described by Mr. Myers, 4 but this parasite was not studied 
intensively until 1918, when the writer undertook to discover the details 
of its life history. This work, with many interruptions, has continued 
to date. The present paper summarizes the data collected on this 
parasite since 1914. 
ECONOMIC IMPORTANCE 
From the standpoint of economic importance Platygaster vernalis 
stands first among the many species of parasites that normally attack 
the spring generation of the Hessian fly in the Middle Atlantic States. 
Percentages worked out for various species of Hessian fly parasites have 
shown that P. vernalis is more effective than any other species attack¬ 
ing the spring generation of the fly in this region. 
Table I.— Percentage of Hessian flies killed by Platygaster vernalis for the years IQI$ to 
IQ20, inclusive, together with the total puparia examined in order to obtain these data , 
with the average and total for the entire period 
Year. 
Percentage 
killed by 
vernalis. 
Number of 
puparia ex¬ 
amined. 
40. IO 
IS* 53 
iS -73 
19.99 
24.68 
2 7*34 
2,582 
2,285 
2,143 
6 , 93 ° 
2,297 
2,419 
1016. 
1017 . . . .... 
1018. 
y .. 
1020. 
y ... 
Average. 
23.89 
18,656 
1 Accepted for publication Aug. 15, 1922. 
2 The writer wishes to express his appreciation of the assistance rendered by the late W. R. McConnell 
and by P. R. Myers in contributing useful suggestions during the progress of the work and in helping 
to rear and determine much of the material used; he also wishes to thank Dr. R. W. Leiby for helpful 
criticisms, Messrs. R. M. Pouts and H. D. Smith for the determination of many of the parasites, and 
Miss Esther Hart for the drawings of the adult, head, and antennae. 
* Order Hymenoptera, superfamily Serphoidea, family Platygasteridae. 
4 Myers, P. R. a new American parasite op the hessian fey (mayetioea destructor say). In 
Proc. U. S. Nat. Mus., v. 53, p. 255-257* 1917. 
( 31 ) 
Journal of Agricultural Research, 
Washington, D. C. 
adv 
Vol. XXV, No. 1 
July 7,1923 
Key No. K-zog 
