ii6 



larvse are white or greenish maggots which mine the leaves 

 of those plants. There may be several larvae in a leaf and 

 by their devouring the middle layers of tissues transparent 

 patches result, covered only by the upper and lower 

 epidermis. After a while these patches become browm and 

 the functions of the leaves are very greatly reduced. The 

 larvse turn into yellow^ or yellow-brown pupa:^ shaped some- 

 what like minute barrels, and are found sometimes in the 

 leaves but mostly in the soil. The Insect w^inters in the 

 pupa buried a few inches beneath the ground. This fact 

 is of value wdth regard to preventive measures and deep 

 trenching in winter betw^een the original row^s and burying 

 the soil therein containing the pupae will destroy many 

 of the Flies w^hich w^ould otherw-ise emerge. The mixing 

 of gas lime with the soil adds to the effectiveness of this 

 measure. Screening the young plants with cheap muslin 

 when first put out protects them from the Flies until they 

 are w^ell established, and less liable to suffer severely from 

 the Insect. Picking off and burning the mined leaves will 

 destroy the larvae, but in bad attacks the depletion of the 

 foliage by this method would be too great. All infected 

 celery tops should be burnt and not cast aside on refuse 

 heaps. Theobald recommends spraying with nicotine; a 

 useful formula is i oz. of 98 per cent, nicotine, and ^ lb. of 

 soft soap to 10 gallons of water. Various preparations of 

 nicotine are obtainable and so long as the above propor- 

 tions are maintained it matters very little which is used 

 (15). It is best to spray in the evening and when the 

 foliage is not too dry, the spray is said to soak through 

 the epidermis and kill a large number of the larv^. 



The Cabbage Root Fly {Chortofhtla brassicae) (7' is 

 one of the worst pests of cabbage and cauliflowers, and 

 may also attack radishes, turnips, swxdes and stocks. 

 Growth of the affected plant is checked, the leaves flag and 

 discolour, the roots are largely destroyed, and the plants 

 die. The Fly is an ashy-grey Insect not unlike the House 

 P ly in general appearance and measures about 4in. long. 

 The winter is passed through in the pupa stage and the 

 first brood of Flies appear in April or the beginning of 

 May and there are most probably three generations in a 

 year. The eggs are visible to the naked eye, and are laid 

 close to, or on the plant, usually iust below the surface of 

 the soil. The larvae are typical Fly maggots,, w^hite or 

 pale yellowish, and about Jin. in length when mature. 



