PROCEEDINGS OF THE 



ENTOMOLOGICAL SOCIETY OF WASHINGTON 



VOL. 24 MAY 1922 No. 5 



A PRELIMINARY ACCOUNT OF TWO SERPHOID 

 (PROCTOTRYPOID) PARASITES OF THE HESSIAN FLY. 



Bv CHAS. C. HILL, Bureau of Entomology. 

 INTRODUCTION 



The Serphoids (Proctotrypoids), (Polygnotus) Platygaster 

 vernalis Myers and (Polygnotus) Platygaster hiemalis Forbes, 

 two important parasites of the Hessian fly, Phytophaga destruc- 

 tor Say, have been confused in the past as the same species by 

 entomologists of this country. Although Webster (19) 2 pre- 

 dicted more than one species of Polygnotus as being involved 

 with the Hessian fly, it was not until 1917 when Myers (27) 

 published his description of Polygnotus vernalis ^ that two sepa- 

 rate species were definitely distinguished. Recently, however, 

 many inquiries concerning them have arisen among workers on 

 the Hessian fly because of the similarity in appearance of their 

 adult stages and the lack of information concerning their 

 respective life histories. It has, therefore, been deemed 

 advisable to publish without further delay a brief treatise on 

 these two species rather than to await the completion of the 

 more exhaustive investigations under way. 



In a- recent article on the genus Platygaster Latreille by 

 Fouts (29), the genera Polygnotus Forster and Platygaster 

 Latreille are declared synonymous, with priority given to Platy- 

 gaster Latreille. Both species under discussion, therefore, 

 rightly belong to the genus Platygaster. 



In the following account the life history observations were 

 made on material reared in confinement from carefully de- 

 termined adults. Nearly all the phases of development were 

 also obtained from the field for comparison and checking of 

 results. 



HISTORY 



Herrick (1) in 1841 was the first investigator to record the 

 occurrence in this country of a parasite which oviposited into 



'The author wishes to express his appreciation for kindly criticisms lu 

 Mr. V. R. Myers, Mr. A. B. Gahan and Dr. R. \Y. I.eilu. 



-Reference is made hy number (italic) to Bilil'nuraphy, p. 115. 



