136 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



The Wheat Joint-worm * 



For the last sixty years the joint-worm has been known as 

 a serious pest of wheat throughout the wheat-growing region 

 east of the Mississippi River, the damage varying from a 

 slight injury which is hardly noticeable, and which may escape 

 observation for several years, to an almost total destruction of 

 the crop. 



The adults appear in April, May, or early June, according to the 

 latitude, and are small black, four- winged flies about one-eighth 

 inch long, with the joints of the legs and feet yellow. They look 



something like 

 small, winged black 

 ants (Fig. 99) and 

 curiously enough 

 belong to a family 

 whose members are 

 almost all parasitic 

 on other insects, so 

 that before they had 

 been thoroughly 

 studied they were 

 thought to be para- 

 sites of the Hessian 

 fly. The females 



lay their eggs in the stems, generally selecting the uppermost 

 joints that have appeared at that time. " The young worms 

 develop rapidly, each in a little cavity within the straw. Often 

 knots, swellings, and twistings occur in the straw at the point 

 of infestation; again there is little sign of the insect's presence 

 except a slight discoloration or a little deviation of the fibres 

 and grooves of the straw from their natural course. When the 

 infested section is split with a knife it is found to be brittle and 



* Isosoma tritici Fitch. Family Chalcididce. See J. S. Houser, Bulletin 

 226, Ohio Agr. Exp. Sta.; and F. M. Webster, Circular 66, Bureau of Ento- 

 mology, U. S. Dept. Agr. 



if, 



FIG. 98. a, wheat-straw affected by joint-worm; b, 

 adult as seen from above. (After Riley.) 



