17 



and, besides, the fields were closely watched for Isosoma grande. On 

 June 2, liftj-one days after, I found a female of Isosoma grande in the 

 inclosure and in the act of ovapositing- in the now full-grown wheat 

 plants. Others were obseryed similarh" engaged during the follow- 

 ing fortnight, and when the straw was ripened it was cut off and 

 placed in glass jars. I had thus again reared the one supposed species 

 from the other. During the following winter man}" adults were reared 

 from these straws, but all were of the one form (/. t /•it lei Rile}^), and 

 I had reared the two forms twice from each other, leaving now no 

 further doubt that they were simply two generations of the same 

 insect, besides showing that as the spring generation is without wings 

 and can not fly from one field to another, a simple rotation of crop on 

 the part of farmers would result in keeping the insect so reduced in 

 numbers as to place it out of necessary consideration as a wheat- 

 destroying insect. 



In all of my own rearings of both forms of this species I did not 

 secure a single male, and of the large number reared at the Depart- 

 ment of Agriculture at Washington, from material furnished b}^ me, 

 but three individuals of this .sex were obtained. "• 



riley's name, isosoma tritici, inval,id. 



In a more recent stud}" of these insects, * Dr. L. O. Howard found 

 that the species described by Dr. Fitch as Isosoma tritici was a valid 

 one. This being the case, Riley's name must no longer be used, and 

 the later one, Isosoma grande, thus covers both. Doctor Howard has 

 given the name mimitimi to the wingless spring form, and this name 

 will hereafter be used in this paper. 



LIFE HISTORY. 



The insect passes the winter in the center of the straw, just above 

 the joint, in the pupal stage. Rarely an adult will emerge in late 

 autumn, but if kept indoors others will appear during December, the 

 most during January, showing that thej^ are ready to appear during 

 the first settled warm weather in spring. In further proof of this, I 

 have found that as the winter advances the}' require less time indoors 

 in which to develop than if the straws are brought in in December, 

 thus showing that, while subject to all of the influences of winter, they 

 are undergoing a change that carries them nearer to maturity. With 

 the settled spring weather they eat a round hole in the straw and 

 make their way forth. As males are few they rarely pair, if at all, 

 but are ready to begin oviposition as soon as out of the straw. They 



« Report U. S. Comm. Agr. 1886, p. 573, footnote. 



& Grass and Grain Joint-worm Flies and their Allies, Tech. Ser. 2, Piv. Ent., 

 U. S. Dept. Agr. 



7327— No. 42—03 2 



