SERPHOID AND CHALCIDOID PARASITES OF THE HESSIAN" FLY 9 



involved in this instance, but in the absence of specimens the facts 

 given by Pospjelov are too meager to warrant a definite conclusion. 

 All specimens from Russia seen by the writer have been hiemalis, 

 but there appears to be no good reason why zosine should not occur 

 there also. 



The studies, in France by Paul Marchal, of polyembryonic develop- 

 ment in what he supposed to be Polygnotus mdnutus in reality deal 

 with Platygaster zosine, as will be shown in the discussion of the 

 latter species. 



In a recent paper Hans Blunck states that specimens reared by him 

 from Mayetiola phalaris in Pomerania were identified by Ch. Fer- 

 riere, of the British Museum, as being probably Platygaster hiemalis 

 Forbes, and that others from the same rearing were sent to L. Biro, 

 of Budapest, who identified them as Polygnotus minutulus Dalla 

 Torre. According to Blunck the material identified by Biro was 

 later seen by Ferriere and found to be the same species as that which 

 he had called Platygaster MemaUs. As already pointed out, these 

 two names refer to the same species, and although the present writer 

 has seen none of Blunck's material, it is highly probable that the 

 identification as P. hiemalis is correct. 



The many references to hiemalis in American literature were satis- 

 factorily reviewed in a paper by Hill in 1922. In some instances the 

 species may have been confused with zosine, but for the most part 

 the records since the Forbes description have probably been based 

 on correct identifications. Many of the references add only new dis- 

 tribution records. Webster has given some account of attempts at 

 introduction of the species from one part of the country into another, 

 and various authors have made more or less important contributions 

 to a knowledge of its life history, but ft was not until the careful 

 work done at the Carlisle (Pa.) laboratory of the Bureau of Ento- 

 mology was published in a series of papers by Hill and Leiby between 

 1922 and 1926 that the life history and importance of the species in 

 America was understood. This information is well summarized in 

 the paper by Hill in 1926. 



HOSTS AND LITE HISTORY 



Platygaster hiemalis has long been known as a primary, internal, 

 gregarious parasite of the hessian fly and only recently has been re- 

 corded by Hans Blunck as a primary parasite of Mayetiola phalaris 

 Barnes. 



It is said to deposit from 1 to 8 eggs in a single egg of its host, 

 Development may be either monembryonic or by process of twinning 

 and always takes place in the body cavity of the host larva instead 

 of in the mid intestine as in the case of P. zosine. When full grown 

 the larvae form individual cocoons closely crowded together within 

 the host puparium, and as many as 23 parasites have been known to 

 emerge from a single puparium. 



This species attacks the fly in the autumn. Oviposition takes place 

 in eggs of the overwintering generation of the fly, but the embryonic 

 development is retarded and development of the larva does not take 

 place until midsummer of the following year. The parasites pupate 

 in late July and early August and by the first of September are ready 

 to emerge as adults. According to' Hill (1926) its seasonal history 



