27 
The adult insect is a minute, black, four-winged fly, measuring in 
leneth from an eighth to less than a quarter of an inch, and closely 
resembles in appearance its own Hymenopterous parasites and also the 
parasites of the Hessian fly and like insects. The galls usually occur 
in groups of three or four, and sometimes in large numbers together, 
greatly deforming and weakening the stem. 
On cutting these galls open they will be found to contain when 
mature the joint-worm larva, yellowish white in color, with its jaws 
or mouth-parts tipped with brown. In the larval and pupal stages 
this species resembles its ally, the straw-worm, /sosoma tritici. This 
species is believed to be single-brooded, and to hibernate in its galls in 
the wheat stems in the larval stage, transforming to pupa and adult 
insect in the following spring or early summer. 
THE WHEAT STRAW-WORM (lIsosoma grande, Riley). 
This insect (figs. 14, 15, 16) is very closely allied to the joint-worm. 
It is distinguished, however, by its habit in living free within the hol- 

Mah or, 
Fai 
i ‘ek 
rt 

Fig. 14.—Wheat straw-worm (Jsosoma grande); a, female inserting her eggs; b, section of wheat stem 
showing point reached by oviposition; c, pupa; much enlarged, c, more enlarged (after Riley). 
low stems or culms of wheat, and producing no gall or deformation in 
the walls of the stem, as do the former species. Its work within the 
stem is indicated by the eaten and torn inner surface, and as a rule it 
does not occur in as great numbers as does the joint-worm. It win- 
ters in the stem in the pupal stage instead of the larval stage, as does 
the joint-worm, and is double-brooded. 
Difference in appearance of the two broods.—The adults of the two 
broods of this insect are quite dissimilar in appearance, and have been 
described as distinct species. The adults, consisting of both sexes 
coming from the over-wintered pup, are rather minute, and the 
females are wingless or with the wings greatly aborted and function- 
less. The eggs of this brood are deposited about the last of April or 
early in May near the embryo head of the wheat, which at this season 
132 
