DIPTERA OR TRUE FLIES. 



219 



ing the young plant: they lie lengthways up the plant, and 

 reach one-fourth of an inch in length.^ The puparia are found in 

 May, from which the fly comes out in July. The imago is very 

 likp the Onion Fly: the thorax is 

 greyj with pale sides and with 

 stripes al)ove ; abdomen ashy -grey 

 with an indistinct dorsal stripe ; 

 legs black with pale tibiae ; abdomen 

 hairy. The female is entirely ashy- 

 grey, posterior and middle femora 

 and tibisB pale. The attack often 

 follows on fallow land, and it has 

 been noticed to occur after the land has been dressed with pond 

 mud. Probably couch-grass harbours this fly. Where it is prev- 

 alent, as in some Fen districts, the seed should be sown thickly. 



The Mangold Wubzbl Fly (Chortophila (Psgomyia) bet*). 



Amongst the pests common to Mangolds and Beets the Wurzel 

 Fly is perhaps the most important. This insect is an ashy- 



FiG. 110. — Wheat-bulb Fly 

 5, Larva ; c, puparium 



Fig. 111. — Mangold Fly (Chortophila ietCB). 



1 and 2, Male, nat. size, and mag. ; 3 and 4, female, nat. size, and mag. ; 5 and 6, 

 larva, nat. size, and mag. , 7 and 8, puparium, nat size, and ma^. (Whitehead.) 



grey fly with black bristles, very similar to the Onion Fly in 

 general appearance. They occur as early as May, when they 



' Some now and then reach one-third of an inch in length. 



