yo Second Report on Economic Zoology. 



Life-history of the Cabbage Eoot Fly. 



The fly Phorhia hrassicas (Fig. 9, a), tlie parent of the Cabbage 

 lioot-maggot, belongs to the family of two-winged insects (or Dvptcra) 

 known as Anihomijidai. It in general resembles a " house-fly," but is 

 rather smaller in size ; its body is about a fourth of an inch long. The 

 male is dark ashy -grey with three broad dark stripes on the surface 

 of the thorax and a wide dark dorsal stripe on the abdomen, dilated 

 at the upper margin of each segment, which is marked with a narrow 

 transverse dark stripe ; the whole body is bristly and the eyes nearly 

 meet in the middle of the head ; the legs are black and very bristly, 

 with a prominent tuft of bristles at the base of each hind femur 

 below. The female is paler ashy -grey, with very indistinct thoracic 

 and abdominal stripes, often absent, and the eyes are widely separate, 

 and the apex of the abdomen is pointed. The female has not such 



Fig. 9. 



a, The Cabbage K^ut I'ly {Flwrbia brasska', Bouche) ; b, the imparium. 



marked characters as the male, and can only be identified by the 

 specialist. 



The flies appear first of all at the end of April and on to May. 

 I have seen them in warm weather as early as April 20th. They 

 also occur in June, and successive broods appear later. Certainly 

 two and probably three generations occur during the year. If there 

 are no cabbages to oviposit on then they place their eggs on wild 

 crucifer roots. 



The female creeps down into the earth around the plants and 

 places her eggs in clusters close to or upon the roots, using the 

 extensile ovipositor to aid her in this process. At other times they 

 are laid (if the ground is firm and close) on the soil close to the 

 plants. Apparently fifty-five is the normal number of eggs laid by 

 each female (Slingerlaud). 



