250 



DIPTEEA OR TRUE FLIES. 



stops oviposition. If possible, it is advisable to sow the seed 

 sufficiently thinly, so as not to necessitate thinning until late in 

 the season. Purifying the beds in winter with gas-lime or 

 vaporite is also valuable as a preventive of future attack. 



Family TRYPETIDiE. 



The Celery Fly (Acidia heraclei). 



The blistered leaves we see so often on celery and parsnips 

 are caused by a small fly which belongs to the family T)-y- 



PiG. 143.— Ckleby Fly {Arhilix lieradci). 

 1, Ima,L;(> ; 2, larv.T, mag. ; 3, piiita, iiat. size ; 4, leaf mined by lanii?. 



pefidir — flies which have mottled or ornamented wings. On 

 examining a blister, we find, within, one or more white larvfe 

 feeding on the soft mesophyll layer between the upper and 



