INSECTS INJURIOUS TO SMALL GRAINS 



137 



woody in character, and contains from 3 or 4 to 20 or more yel- 

 lowish larvae, about one-eighth inch long when full-grown. These 

 larvae remain in the straw until the following spring, when they 

 issue as adults and commence again the life cycle in the new crop. 

 The damage is done by the worms cutting off the sap supply 

 from the head, causing it to become shortened, containing 

 comparatively few kernels, and such kernels as develop are apt 

 to be small and shriveled from lack of nourishment. Also because 

 of the brittlcness of the straw high winds are apt to break much 

 of it down." Gossard. 



The presence of the pest is always indicated at threshing by 



FIG. 99. Wheat straw-worm (Isosoma grande Riley): a, ventral view; b, side 

 view of larva; c, antennae; d, mandible; e, anal segment, ventral view; /, 

 adult female; g, fore-wing; h, hind-wing; i, aborted wing. (After Riley.) 



short, hard bits of straw, containing the larvae, which are carried 

 out with the grain instead of going over in the straw. It has 

 usually been considered necessary to separate and burn these, 

 but Professor F. M. Webster finds that the larvae in them are 

 probably killed in threshing, as he has been unable to rear 

 adults of cither the joint- worm or its parasites from such bits of 

 straw. 



Control. A rotation of the wheat crop is of primary impor- 

 tance in the control of this pest, and where wheat is not planted 

 on the same land and is sown as far from that of the previous 



