122 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



slight injury which is hardly noticeable, and which may escape 

 observation for several years, to an almost total infestation 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. 102) 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 parasites of the Hessian fly. The females 

 lay their eggs in the stems, generally selecting the uppermost 



joints that have ap- 

 peared at that time. 

 " The young worms 

 develop rapidly, each 

 I 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 



wheat-straw affected by joint-worm; except a slight discol- 

 6, adult as seen from above. (After Riley.) or&i[on Qr & ^^ d& _ 



viation 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 woody in character, and contains from 3 or 4 

 to 20 or more yellowish 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 cut- 

 ting 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 brittleness 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 

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



