DIPTERA OR TRUE FLIES. 



239 



The larvae live in the roots of plants and set up decay. The 

 most important are the following : the Onion Fly (Phorb/a 

 cepeiarum) ; the Cabbage-root Flies (P. Jjrasaicii', A. rarlicum, and 

 A. floralis) ; and the Wheat-bulb Fly (Hyleinijia coarctata). 



The Onion Fly (Phorbia cepbtoeum). 



One of the most serious difficulties the onion-grower has to 

 contend with is the Onion Fly, whose larvae cause the maggot 

 in onions and their speedy decay. The onion fly is an ashy- 

 grey fly with black bristles and hairs, and with three black 

 stripes on the thorax ; the abdomen has a row of large black 

 spots along it ; the face is silvery-white, and the antennte are 

 black ; the female has a yellow face, and is generally more 



Fig. 134. — Onion Fly (Phorbm ccpetorum). 

 a and b, Larva, nat. size, and magnified ; c and d, puparia ; e, imago. 



oohreous in colour. The onion fly appears in April and May, 

 and has several broods during the year. The female lays her 

 ova near the young onions, and later on in the year on the 

 onion itself. The young maggots at once eat the young onion 

 below ground, and later feed inside until they are quite 

 hollowed out. Some plants are killed rapidly, but large onions 

 remain some time in a diseased state. When young onions are 

 attacked the maggots pass rapidly along the row. When an 

 older onion is destroyed, if the maggots are not mature they 



