216 



DIPTEEA OE TRUE FLIES. 



The Onion Fly (Phorbia cbpetorum). 



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

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

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

 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-whjtCj and the antennae are 

 black ; the female has a yellow facej and is generally more 

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

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

 ova on the neck of the young onions, and later on in the year 



Pia. 108. — Oniok Flt (PhorUa cepetorum) . 

 a and b. Larva, nat. size, and magnified ; c and d, puparia : e, imago. (Whitehead.) 



on the onion itself. The young maggots at once eat their way 

 into the onion and feed off its contents until it is quite hollowed 

 out. Small plants are usually killed rapidly, but large onions 

 remain some time in a diseased state When an onion is 

 destroyed, if the maggots are not mature they leave it and pass 

 to the next onion through the ground. Pupation takes place in 

 the ground, and in the decaying onions, — the pupa being in a 

 chestnut-brown puparium case, as in ail the Proboscidea. At 

 the end of the year the larvae of the last brood all pupate, and 

 pass the winter as pupae in the ground, some few being har- 



