F. W. Dry 83 



6. The several broods of the Midge do not succeed each other too 

 quickly or overlap too much for it to be impossible, by choosing the right 

 time, to make a census for each brood in an area such as that in which 

 I worked. 



II. Life-history of the Swede Midge. 



The life-history of the Swede Midge and the distortion which it 

 causes to the swede plant are described by Mr T. H. Taylor in Cabbage- 

 Top in Swedes 1 . The following short account is based on that in 

 Mr Taylor's paper. 



The flies are first found in swede fields in June. The eggs are laid 

 in strings and clusters mostly near the base of the leaf-stalks, but some 

 on the leaf-blades ; the younger leaves are almost always the ones to 

 be attacked. The eggs hatch in about four days and the maggots feed 

 on the superficial tissues. The larval stage lasts about three weeks. 

 When full grown the maggots go down into the ground and the flies 

 come out, in the case of the summer broods in from two to three weeks. 

 The normal number of broods for the season appears to be three, although 

 in the hot summer of 1911 there were four broods. The winter is spent 

 in the soil. 



Mr Taylor describes and figures the distortion to the plant caused by 

 the maggots. (Cf. figs. 2 and 3, Plate XVIII, of the present paper.) 

 He says " In three or four days after the larvae have started to feed the 

 plant begins to show signs of being damaged. The stalks of the affected 

 leaves become swollen, and bending sharply inwards across the top of 

 the plant, press upon and compact the terminal bud. Moreover, the 

 leaf-blades, at those areas where the larvae are feeding, become 

 delicately crumpled, thus resembling the leaves of a savoy cabbage." 

 Mr Taylor also proved that the Swede Midge was one cause of what 

 he calls "many-neck" in swedes, that condition in which the plant 

 has several necks or main shoots instead of the single one of a normal 

 plant. 



My own observations agree with Mr Taylor's account. I think, 

 however, that in 1913 the time elapsing between the maggot's entering 

 the soil and the emergence of the fly was often as long as a month. 

 It will be seen that in this paper I am concerned only with the crumpled- 

 leaf condition, and not with " many-neck." Besides the Swede, Brassica 



1 Publications of the Yorkshire Council for Agricultural Education, No. 82. 



6—2 



