THE DIPTERA 



329 



placed around their stems close to the ground (Fig. 349) and usually 

 give good results. These disks may be cut by hand from ordinary tar 

 paper, though where many are required, the use of a cutting stamp is 

 advantageous. The piece is usually cut six-sided for economy of the 

 paper, and from one corner a cut to a little beyond the center is made 

 and also a short cut crossing this at the center, giving four points between 

 which the stem is passed. The disk is then pushed down to the ground. 

 In cultivating later, care should be taken to brush off any dirt which 

 gets on the upper side of the disk as in such cases the fly often attacks 

 the plant. The destruction of all the refuse of the plants on harvesting 

 the crop, and also of all mustard and other cruciferous plants near by, 

 is desirable to prevent further increase of the insect there before winter. 



Various other treatments have been suggested but have not given 

 entire satisfaction. The tar-paper disks are not entirely effective as 

 protectors, and to apply them carefully requires time, but they give the 

 best results of any control method thus far discovered. 



Recently, one ounce of corrosive sublimate dissolved in 10 gal. of 

 water, poured around the bases of the plants, has given quite good results. 



FIG. 350. Adults of the Onion Maggot (Hylemyia antiqua Meig.), twice natural size. 

 (From Britton, Eleventh Rept. Ent. Conn. Agr. Exp. Sta. 1911.) 



The Onion Maggot (Hylemyia antiqua Meig.) is often a serious pest, 

 mining in the bulbs .and quickly causing their decay. Like the Cabbage 

 Maggot, it is a European insect but has been known in the United States 

 for many years and is now widely distributed. Details of its life history 

 are not as well known as could be desired, but it is probable that the 

 insects pass the winter as pupae and perhaps as adults also. The flies 

 (Fig. 350) lay their eggs on the onions soon after they come up in the 

 spring, and these hatch in a few days forming whitish maggots which 

 attack the bulbs and feed during a period varying according to weather 

 conditions for from 2 to 4 or 5 weeks, after which they pupate in the 

 ground, or, occasionally, in the outer layers of the onion itself. During 

 the summer, this stage continues about 2 weeks, after which the adult 

 flies appear and in about 10 days begin to lay eggs for a second generation. 



In some parts of their range there are probably only two genera- 

 tions a year, but elsewhere there seem to be three. The injury caused 

 by this insect when abundant is sometimes large, entire fields con- 



