DIPTERA OR TRUE FLIES. 



241 



The Cabbage Fly (P. hrassiva-) is 



-The Cabbage-root Fly (Phorhia 

 brassicK) 



spring as well as puparia. 

 ashy-grey, and hatches 

 from the puparium in 

 about three weeks : the 

 male has a black stripe 

 down the abdomen and 

 three on the thorax. 

 The fly galls on tur- 

 nips must not be con- 

 fused with those of 

 the Turnip-Gall Weevil 

 (Ceutm-hynchus sulcicol- 

 lis). The Eadish Fly 

 {A. floralis) has a spiny maggot; A. radicum (fig. 133, 4), a 

 yellowish grub with two black points at the end of the tail. 



Prevention and Treatment — Little can be done when the 

 grubs are once installed 

 in a plant. Where cab- 

 bages are grown year 

 after year on the same 

 land, the soil is sure to 

 become contaminated 

 unless cleaned annual- 

 ly ; for this gas-lime, or, 

 better, vaporite, is re- 

 commended. Dibbling 

 in the plants with a 

 little soot and lime is 

 a good deterrent ; and 

 broadcasting the same 

 over young plants not only keeps off these flies but slugs as 

 well. All the diseased cabbage stalks and roots ought to be 

 burnt, instead of being put up in heaps to rot, when many of 

 the grubs will escape and pupate. Card discs are sometimes 

 used, as shown in fig. 136, to prevent egg-laying. 



Q 



Fig. 136.— Card disc to prevent Ego-layikq 

 OF Cabbage Fly. 



