79 



NATURAL HISTORY OF THE WHEAT STALK WORM. 



After carefully looking over what has been written of our American 

 species of Isosoma, to which the Joint-worm belongs, and a comparison 

 of the Wheat-stalk insect with the others both in structure and habits, 

 I am convinced that it is a new species, and have named it Isosoma 

 Allynii as at the head of this article. I do not expect to give here a 

 scientific description, but would refer the reader to the pages of the 

 Canadian Entomologist for that, as I believe it best here to give only so 

 much of a description of the different stages and manner of work as 

 will enable any one to recognize the insect. The manner of work has 

 already been given, so that we will begin with 



THE LARVA. 



In size, shape and color, this is almost identical with the larva of 

 Isosoma Hordei. It is a small yellow or pale-orange footless worm, 

 about .15 of an inch long, rather slender, and tapering slightly towards 

 either end. 



Under the better pocket-lenses a distinct tranverse head may be seen 

 on one end of the body, armed beneath with a pair of brown jaws. 

 Though footless, when in motion, it seems to push out little projections 

 along the sides of the body by the aid of which, and a wriggling move- 

 ment, it is capable of some progression. These are found on the inside 

 of the stalks usually just above a joint, occasionally more than one in 

 a place, but generally if there is more than one in a stalk they are 

 in different internodes. In a previous part of this article I have stated 

 that they are seldom found in the space between the upper joint and 

 the head. I have "found a very few of the grass form in that position, 

 but cannot recall now finding any of the Wheat-stalk worms in that 

 position. When about to pupate they are generally very close to the 

 joint. 



THE PUPA. 



This is at first pale yellowish but finally jet-black, shinning, from, 

 .10 to .12 of an inch long by about .02 of an inch wide. The pupa that 

 formed in the summer, or rather that produced the flies in the summer, 

 were in various parts of the gnawed chamber, but I notice those in the 

 stubble the last of November are pretty well down in the tissure of the 

 joint. In position, the pupa rests with the head upward. 



The time of change from larva to pupa has been spoken of before. 

 I cannot say just what time that change took place, with those not 

 hatching out during the summer, for my observations on my specimens 

 were not carried beyond August 30th, when a number of them were still 

 in the larva state. Some further examinations were made in the 

 grasses, but not in the wheat till the last of November, when all remain- 

 ing were found to be pupse. Of those that went through with all of 

 their changes during the summer, none were observed as pupa up to 

 July 8th, and July 20th a few perfect insects were observed. At tliis 

 season, then, the pupal period did not last more than 13 days, and per- 

 haps much less than that. 



