THE DIPTERA 313 



as by this time the plants may be a number of inches high, the eggs 

 can be laid at different heights on the plant, and the larvae will pass down 

 to the joints immediately below the leaves on which the different eggs 

 are laid. Feeding at these joints continues during the spring and the 

 flax-seed stage is reached at or before harvesting time. Some of the 

 flax-seeds will be in the straw cut and harvested while many more will 

 remain in the stubble and the flies emerge from the flax-seeds during the 

 early fall as already indicated, ready to attack the fall-planted wheat as 

 soon as it comes up. 



In regions where the wheat is planted in the spring, the insect winters 

 in the flax-seed stage in stubble and volunteer wheat, and the adults 

 appear in May. The second generation quickly follows the first, particu- 

 larly in wet seasons, and there seems to be no period of delay such as 

 occurs during midsummer in the fall-wheat regions. 



Control. The Hessian Fly has numerous parasites which are undoubt- 

 edly of much value, as where great loss occurs these insects are few in 

 number. It is so often the case, though, that the fly is abundant, that 

 parasites can not be relied upon and other measures, largely preventive 

 in their nature, must be taken. 



It is evident that, if fall planting can be delayed until the adults 

 which appear at that time are gone, the crop will be protected from 

 attack. To carry out this plan, however, latitude, elevation and humid- 

 ity perhaps, as well, must be taken into consideration. Investigations 

 along this line, though far from complete, now indicate that it is generally 

 safe to plant wheat in northern Michigan after the first of September: 

 in southern Michigan and northern Ohio, about the twentieth of that 

 month: in southern Ohio, after October 7: in Kentucky, after October 

 15 : and in Georgia, from the last week in October to the middle of Novem- 

 ber. Thus in general, the farther south, the later the planting date 

 should be, though very high land in any region can probably be planted 

 earlier than low land if the area and elevation are sufficient to give it the 

 more northern conditions. 



The rotation of crops is also of advantage, driving the flies elsewhere 

 to lay their eggs and making them more liable to destruction while 

 en route. 



Many of the flax-seeds are left in the stubble at harvesting and 

 any method of destroying these is beneficial. Where the grain is cut 

 rather high and a mowing machine is then run over the field, cutting 

 the stubble as close as possible, burning this cut stubble after a few days' 

 drying is effective. Unfortunately, however, the general custom of 

 planting grass and clover in such fields, to come up as the grain progresses 

 toward harvesting, too often makes this control impracticable. 



Volunteer wheat as it is called, coming from grain scattered through 

 and around the wheat fields by accident, starts early and provides plants 



