4 BULLETIN 808, U. S. DEPARTMENT OF AGRICULTURE. 



festation, as the plants are thus made much more top-heavy. As the 

 growing larvae consume proportionately large amounts of sap, the 

 developing wheat kernels are constantly robbed of their nourish- 

 ment and suffer accordingly. 



A field of wheat badly straw-fallen usually is attributed to the 

 depredations of the Hessian fly by the average farmer, and very 

 often the fly is wrongly credited year after year, in the States east 

 of the Mississippi River, with serious and widespread injury that is 

 chargeable to the jointworm. 



HOST PLANTS. 



During repeated trials covering a number of years this species was 

 never induced to breed in any plant but wheat. It never has even 



Fig. 1. — The wheat jointworm (HarmoUta tritici) : Adult female. 

 Greatly enlarged. (The head is tilted back somewhat so as to 

 show the groove in front.) (Author's illustration.) 



been observed to attempt oviposition in any other plant. The stems 

 of barley and rye particularly do not differ greatly from wheat, but 

 they seem to be distasteful to tritici. 



LIFE HISTOKT. 



There is only one generation a year. The adults (fig. 1) emerge 

 in May and deposit their eggs in the stems of growing wheat just 

 about the time the heads begin to appear. The life of adults lasts 

 from a few days to a week or more, depending upon the temperature. 

 The eggs (fig. 2, a, 5) hatch in about 10 days. The larvae mature in 



