117 



They commence injury by gnawing the outer layers of the 

 young roots, afterwards making tunnels inside the main 

 root; they may also invade the low^er part of the stem. 

 The pupas are about 4 in. long, oval in form, a light or 

 dark brown and are found in the soil close to the plants. 

 x\s regards preventive measures early plants have the best 

 chance of success as they become well set before the bulk 

 of the Flies appear. Earthing the soil around growing 

 plants IS valuable as it causes the development of fresh 

 rootlets, v\iiich serve to replace those already destroyed 

 by the maggots. A cupful of paraffin well mixed with 

 each bucketful of sand, sprinkled round the plants once 

 a week until good growth is made, is to be recommended 

 and it acts as a deterrent, driving the Flies elsewhere. 

 Dusting the young plants with soot is said to be effective 

 and is well worth trial. In Aimerica tarred felt paper discs, 

 slipped round the stems of the young plants and pressed 

 fiat on the ground are strongly recommended. They are 

 said to afford eflicient protection to young plants against 

 the Flies laying eggs thereon. Experiments are being 

 conducted under my direction to test the value of these 

 discs, and if they prove satisfactory, their low cost and 

 the simiplicity of the method will argue strongly in their 

 favour. \\^hen the crop is infested m^uch benefit is derived 

 by pulling up and burning all infected plants as soon as 

 noticed. Furthermiore, all cabbage stumps should be up- 

 rooted straight away and not left to decay; by these 

 means large numbers of larv^ are destroyed which would 

 otherwise escape into the soil to pupate. In very severe 

 infestations I vvould strongly advise discontinuing grow- 

 ing cabbages for one year, and replacing with peas and 

 beans or other distantly related crops. Unless some such 

 course be taken bad infestations may continue for several 

 years in succession, owing to the large num.ber of pup^ 

 the soil contains during the winter, after the season is over. 

 Such pupae are very hard to get rid of as soil dressings 

 such as lime or gas lime are of very little value. Digging 

 over the soil exp>oses considerable numbers of pupae to 

 the attacks of insectivorous birds, while over large areas 

 deep ploughing might possibly effectively bury a large 

 proportion of themi. 



The Onion Fly {Hylc7Jiia cepeto77m?) (^17) is closely 

 related to the Cabbage Fly and is a common pest wherever 

 onions are grown ; it is a greyish Insect very like the 



