10 MISC. PUBLICATION 174, U.S. DEPT. OP AGRICULTURE 



may be greatly modified by climatic conditions, as illustrated by the 

 fact that in the spring-wheat area of northern New York many adults 

 emerge in the spring and are thus enabled to take advantage of the 

 principal egg-laying period of the host in that region. In Oregon 

 hiemalis is said by L. P. Rockwood, in correspondence, to have two 

 generations per year, the first in the late spring and the other in the 

 fall. 



DISTRIBTTIOX 



This species, as has already been shown, occurs in Europe as well 

 as in Xorth America, and it is also said to occur in Xew Zealand. 

 In Xorth America it is probably generally distributed throughout 

 the wheat-growing region of the United States and Canada, with the 

 possible exception of California. According to Webster (1907). an 

 attempt was made to introduce it into California, but it has never 

 been recovered in any of the extensive collections of fly material 

 since made in that State. Definite records of its occurrence have 

 been obtained from practically all the other wheat-growing States 

 of the United States, and also from Ontario and Manitoba in Canada. 



Its distribution in Europe is less definitely known. Specimens 

 from England, from Breslau in Germany, and from the vicinities 

 of Moscow and Leningrad in Russia have been seen by the writer. 

 If statements by Lindeman, Spassky, and other Russian writers are 

 correct, the species also occurs in the Province of the Don Cossacks 

 in southern Russia. Blunck records it from Pomerania in Prussia. 

 These few records indicate as wide a distribution for the species in 

 Europe as in Xorth America, although there are not enough records 

 to warrant the definite assumption that the distribution is as general 

 there as in America. 



The species is recorded as a parasite of the fly in Xew Zealand by 

 David Miller and. together with Pleurotropis epigonus* is credited 

 by him with controlling the fly. 



IMPORTANCE 



Platygaster hiemalis is believed to be the most efficient parasite of 

 the hessian fly in Xorth America, and it no doubt plays an important 

 role in the control of the pest in certain parts of Europe also. In 

 Xorth America it is practically the only parasite that attacks the 

 fall generation of the fly. Hill (1926) states that in the Middle At- 

 lantic States over a period of 9 years an average of 28 percent of the 

 flies of the fall generation were parasitized by it. It is also said to 

 be a very efficient enemy of the fly in the Pacific Xorthwest. 



PLATYGASTER ZOSIXE WALKER 



(Fig. 2) 



Platygaster zosine Walker. Ent. Mag. 3: 266, 1836: Myers. U.S. Natl. Mus. 

 Proc. 53 : 255, 1917 ; Kieffer. Das Tierreicb. y. 48. p. 817. 1926. 



Polygnotus zozini Marclial. Ann. Soc. Ent. France 66: 93. 1897; Ashmead, 

 Psyche 8: 137, 1S97. 



Polygnotus minutus Marclial (not minutus Lindeman"). Ann. Soc. Ent. France, 

 66: 91. 1897; Ashmead, Psyche 8: 138. 1897; Howard. Science (n.s.) 7: 248, 

 1898 : Marchal. Bui. Soc. Ent. France 1903 : 90 ; Marchal. Compt. Rend. Soc. Biol. 

 [Paris] 56: 468, 1904; Howard. Science (n.s.) 24: 814, 1906; Marchal, Notice 

 sur la travaux scientifiques, p. 47, 1912. 



