y 



extreme north, notably in Minnesota, and in Manitoba and the North- 

 west Territories in Canada. The Isosomas do not attack the grain 

 plants in the fall, and thus we have a natural division between the two, 

 which is applied in the discussion of these insects in the following 

 pages. 



The Oscinids are not destructive in this country alone, as allied 

 species have long been a serious pest in England, France, Germany, 

 and Sweden. The f rit-lly ( Oscinisfrit Linn.), is some years especially 

 destructive in Europe. The gout-fly ( Chlorops tseniopus Meigen) and 

 the W'heat bulb-fly {Ilyleimjia coarctata Fallen) are both more or less 

 injurious to small-grain crops in England. 



In the preparation of this bulletin the writer has been greatly aided 

 by Dr. Howard and his corps of assistants, both in the Department of 

 Agriculture and also in the United States National Museum, and by Dr. 

 S. A. Forbes in kindly and promptly placing the notes and collections 

 of the Illinois State Laboratory of Natural History at the author's 

 disposal. The writer is also indebted for specimens to Dr. James 

 Fletcher, entomologist and botanist for the Dominion of Canada, and 

 for similar favors received from Prof. F. L. Washburn, State ento- 

 mologist of Minnesota. 



THE GENUS ISOSOMA. 



The grass and grain joint-worm flies belonging to this genus are 

 widely distributed in America, some of the most important ranging 

 from the Atlantic to the Pacific coasts and from Canada southward 

 probably as far as the grains, wheat, rj^e, and barley are grown. 



The genus Isosoma is known to inhabit Europe, Africa, Madeira, 

 St. Vincent, Australia, and Tasmania. In Europe it ranges over 

 Russia, Switzerland, Germany, Austria, and Italy. When the insect 

 faunas of Asia and Central and South America come to be better 

 understood, we shall in all probability find that species occur in those 

 countries also. 



These insects belong to the Chalcididse, a family of parasites whose 

 normal food is other insects in one or more stages of their develop- 

 ment. For a long time entomologists refused to believe that the 

 species of Isosoma and their allies were exceptions to this supposed 

 rule, and Harris firmly believed that Isosoma hordel was a parasite 

 and not the true depredator in barley straw. Dr. Asa Fitch after- 

 wards established the fact of phytophagic habits in I. hordei as well 

 as in several other species, but English and European entomologists 

 were not wholl}' convinced, at least not all of them, up to as late as 

 1882. When the writer began the study of grain-infesting Isosoma 

 in 1884, comparatively little was known of the habits of some of our 

 most common species, and the establishing of the fact of dimorphism 



