400 JOURNAL OF'ECONOMIC ENTOMOLOGY [Vol. 9 



as long or longer than the three preceding segments taken together. 

 The face of /. iritici is somewhat longer and the abdomen broader 

 posteriorly, that is it is not quite as tapering as in /. vaginicolum . 



Most of the adults of /. vaginicolum appear during the month of 

 May. At this time they may be found laying their eggs in the base of 

 the leaf-sheath just above one of the joints, usually near the middle of 

 the stem. Three or four or often as many as fifteen or twenty eggs 

 may be laid close together and when the larvte begin to develop the 

 leaf-sheath becomes more or less swollen. Each larva is enclosed in a 

 firm little oval cell from a quarter of an inch to three eighths of an inch 

 long. The swelling and hardening of the walls of the sheath presses 

 on the stem in such a way as to prevent the sap from flowing through 

 it readily and the plants become stunted and produce only small, 

 poorly-developed heads. If the plants are badly affected or if they 

 are infested early, they may produce no heads at all or the heads may 

 never develop far enough to burst from the protecting leaf -sheath. 

 In some fields eighty to ninety per cent of the wheat stems are infested 

 and the crop loss will amount to from fifty to seventy-five per cent. 

 I have seen some fields so badly injured that they were not considered 

 worth the harvesting and the whole crop was a total loss. If the 

 larval cells are very close to a joint they often cause conspicuous knots 

 and the stem becomes much distorted. These swollen and distorted 

 stems resemble very much the stems that have been injured by I. 

 tritici, but a careful examination will show that the cells occur only in 

 the leaf-sheath, whereas the larvie of /. triiici are found in the walls of 

 the stem of the plant. 



The larvse remain in the stems throughout the summer, fall and 

 winter, and pupate in their cells during April and May. Most of the 

 adults issue in May and early June. 



I have found Isosoma vaginicolum only in the dry farm region. /. 

 grande, which occurs with it there, has a much wider distribution, being 

 found commonly in the wheat fields in the irrigated districts as well. 

 In the well-tilled, well- irrigated fields, however, the injury that the 

 wheat straw worm does is not as important or noticeable as it is in the 

 dry farm regions, where the loss of the young plants due to the work of 

 the first generation of larvae, and the hardened thickened walls of the 

 stems, due to the presence of the summer brood of larvse, affects very 

 seriously the quantity and quality of the yield of wheat. The effect 

 of the work of this insect in the wheat fields in this state is similar to 

 the conditions described by Webster and Reeves in Circular 106 of 

 Bureau of Entomology. 



I have found, both in Utah and California, that if a very young 

 plant is attacked by the larvse of the second generation it maj^ be 



