1904]. 



The Cabbage Root Fly. 



353 



Professor M. V. Slingerland has done very much to dispel 

 this confusion*, both by making clear points in the biology and 

 showing how the pest may be combated with reasonable 

 chances of success. 



The adult fly measures about J in. long, and there are 

 differences between the sexes. The male is dark ash grey, 

 and has three dark stripes on the upper surface of the thorax ; 

 a similar black stripe runs down the abdomen, each segment 

 of which has also a narrow transverse black stripe. The body 

 generally is distinctly bristly. The eyes almost meet on the 

 top of the head. The legs are black and bristly, and as a 

 characteristic each hind femur (thigh) has at its base a tuft 

 of bristles. The female fly is paler in colour ; the dark stripes 

 are fainter or absent ; the eyes do not occupy so much of the 

 head there being a distinct space between them ; the abdomen 

 is pointed. 



The egg is very small but visible to the naked eye, whitish 

 in colour, and narrow oval in shape. The larvae or maggots 

 are white or whitish-yellow and legless ; the head end is 

 pointed, and has two dark curved mouth hooks ; the hind end 

 is truncate, and the last segment carries on its middle two 

 dark spiracles ; all round the edge of this last segment are 

 twelve little projections, which can be seen on examination 

 with a good lens, the two lowest being larger, and forked, this 

 latter peculiarity being characteristic of the species. When full 

 grown the maggot measures J in. ; it becomes a pupa under 

 cover of its last moulted skin, the puparium or case being light 

 or dark brown in colour and oval in shape. 



The females lay their eggs close to the plant, choosing, 

 it may be, a crack in the soil by which they can get below 

 the surface, so that the eggs may be laid as close to the plant 

 as possible. In a week or more, according to the weather, 

 the eggs are hatched, and the maggots first of all gnaw the 

 external layers of the young roots, and then make and occupy 

 galleries in the cortex of the main root. Sometimes the lower 

 part of the stem is invaded, in which case the pith is tunnelled. 

 The maggots have been taken tunnelling in the leaf stalks of 



* Bull. 78, Nov., 1S91. Cornell Univ. Exp. Station. "The Cabbage Root 

 Maggot," by M. V. Slingerland. 



