INSECTS. 



177 



the leaves die. In June the maggots creep out of the 

 leaves, and become pupse in the soil. The flies quickly 

 escape, and two or three generations follow one 

 another in the year. As, however, the leaves are 

 now larger, the later generations only efi"ect a small 

 amount of damage. Preventive Measure : Close sow- 

 ing of the turnips, so that even if many are killed 

 there will still be enough young plants. The Cabbage 

 Root-eating Fly (A. radieum) and the Radish Fly 

 (A. floralis) live as fleshy, wrinkled, dirty white 

 maggots with black dots, in the underground parts 

 of turnip, cabbage, horseradish, radishes, etc. They 

 lead a similar life to the 

 Cabbage Fly {A. brassicce), 

 the cylindrical, smooth, 

 yellowish-white maggot of 

 which lives in the under- 

 ground parts of cabbage, 

 turnip, and rape. The roots 

 attacked swell here and 

 there (Fig. 116), and later 

 on decay ; the leaves of 

 the infested plants first 

 become of a dull leaden 

 colour and then wither. 

 Entire fields of cabbage, 

 rape, or turnips, are often 

 destroyed by cabbage fly 

 maggots. The insect passes 

 the winter in the pupa 

 state ; the flies appear early 

 in the spring, and usually 

 twice more later on. It is therefore most desirable 

 to pull up and burn the infested plants as soon as 

 possible. A proper rotation of crops should also be 

 practised. [The Onion Fly (A. ceparum) maggot feeds 

 within the bulbs of stored onions. The male fly is 

 grey, the female yellow.] 



N 



Fig. 116. — A turnip infested by the 

 Cabbage Fly: A, swellings; G, tunnels. 



