120 INSECT PESTS OF FARM, GARDEN AND ORCAHRD 



appear, if planting be delayed until after that time, but little of the 

 wheat will be injured. Dry weather in late summer and early 

 fall will delay the appearance of the flies, even with normal tem- 

 perature conditions, and the further south, the later 'they appear. 

 From experiments being conducted by the U. S. Bureau of Ento- 

 mology, Professor F. M. Webster states that the following dates will 

 probably be found safe for sowing wheat in average seasons: in 

 northern Michigan soon after the 1st of September; in southern 

 Michigan and northern Ohio, about September 20th; in southern 

 Ohio after the first week in October; in Kentucky and Tennessee, 

 October 10th to 20th; in Georgia and South Carolina, October 

 25th to November 15th. The exact time will also depend upon 

 altitude as well as latitude. 



A rotation of the wheat crop compels the flies when they emerge 

 from the stubble to travel in search of the young wheat plants. 

 Should storms or heavy winds occur, the frail little flies will be de- 

 stroyed in large numbers, whereas if they found wheat immedi- 

 ately available the mortality would be small. 



a b c e 'd 



FIG. 101. Hessian fly: a, egg, greatly enlarged; b, section of wheat-leaf 

 showing eggs as usually deposited less enlarged; c, larva; d, pupa 

 taken from puparium or "flaxseed" e, c, d, e, much enlarged. (After 

 Webster and Marlatt, U. S. Dept. Agr.) 



Inasmuch as most of the spring brood remain in the stubble 

 in the flaxseed stage after harvest, if the fields be then burned 

 over, large numbers will be destroyed. This may be done by cut- 

 ting the grain rather high at harvest, and then mowing the weeds 

 and grass and allowing them to dry a few days before burning. 



