ENTOMOLOGY 187 



field to compact the earth and prevent any flies which may mature 

 from issuing. 



The regular practice of a system of rotation in the growth of 

 crops is of the utmost importance in avoiding damage. Its value 

 may -be offset at times by invasion from neighboring fields of wheat 

 on other farms, but usually comparative freedom from attack will 

 result and the benefit will extend to the other crops coming in the 

 system adopted in checking the insect enemies of these at the same 

 time. 



The supplemental fall brood antedating the principal brood 

 will come to nothing if all volunteer wheat be plowed under or de- 

 stroyed within a few weeks after its appearance. This is of especial 

 value in the North, where spring wheat is grown, and where the 

 brood developed on the volunteer wheat may be the principal means 

 of carrying the insect through the winter. 



The Wheat Midge. The wheat midge is another dipterous en- 

 emy of wheat, allied to the Hessian fly and the wheat bulb-worm by 

 belonging to the same order of insects, but is entirely distinct in ap- 

 pearance and habit. The adult insect is a very minute gnat or 

 midge, not exceeding one-tenth of an inch in length and varying in 

 color from orange to yellow, but tarnished or slightly smoky-tinged 

 on the back above the wings. 



The injury occasioned by this insect to wheat and allied grains 

 is by its orange-yellow larvae or maggots to the forming embryos in 

 the wheat heads. The milky juice is extracted by these larvae from 

 the young kernels without any apparent gnawing of the surface, 

 causing the grain to shrivel and the heads to blight and be imper- 

 fectly filled. On occasions of unusual outbreaks of this insect the 

 crop is sometimes completely ruined, and occasionally the losses over 

 whole States have averaged from two-thirds to three-fourths of the 

 entire yield, or amounting to many millions of dollars. Damage to 

 this extent is, however, unusual, and the wheat midge, while ranking 

 as one of the chief insect enemies of the w r heat crop, is commonly 

 much less dreaded than the Hessian fly or the chinch bug. 



The period of attack of this insect in early summer depends 

 very much on the season, being retarded by cold and hastened by 

 warmth. Ordinarily the fly appears about the wheat by the middle 

 of June, and is present depositing its eggs for two or three weeks. In 

 wet seasons it may even remain in evidence until the middle of Au- 

 gust. Dryness is inimical to it, and unusual moisture is very favor 

 able for its operations. It is especially active on cloudy days and 

 at night. Wheat grown in low, moist land is therefore more subject 

 to injury, and if unusually dry weather prevails during the period 

 when the fly is depositing its eggs, little injury is done to the wheat 

 crop, and, correspondingly, a wet season at the same period is liable 

 to result in greater loss on account of this insect. 



The exceedingly minute, oval, nearly cylindrical eggs, pale red 

 in color, are deposited singly or in clusters to the number of ten in 

 the crevices in the wheat heads, most often at the extremity of the 

 head, and usually in the crevices and openings which lead to the 



