DIPTEEA OK TRUE FLIES. 225 



that the carrots get blighted, and this for two reasons — ^first, 

 we bruise the plants in thinning them, and thus release the 

 smell ; and secondly, by loosening the earth around we expose 

 the carrots more readily to the fly. We should remember in all 

 these pests that the eggs must be laid on the plant, as the 

 larvae cannot travel far. 



Prevention and Remedies. — When thinning is necessary, we 

 should broadcast over the plants sand or ash in which a small 

 quantity of paraffin has been mixed, about a pint to a bushel 

 of sand. This destroys the smell, fills in the crevices, and 

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

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

 the season. Purifying the beds in winter with gas-lime is also 

 valuable as a preventive of future attack. 



The Celery Fly (Tbphritis onopordinis). 



The blistered leaves we see so often on celery and parsnips 

 are caused by a small fly which belongs to the family Try- 

 petidce — flies which have mottled wings. On examining a 

 blister, we find, within, one or more white larvae feeding 

 on the soft mesophyll layer between the upper and lower 

 epidermis, thus clearing out the green mass of the leaf and 

 leaving behind a pale blistered patch. The grubs are the 

 larvae of the so-called Celery Fly, which is a small pale-brown 

 fly, with wings mottled with dark brown, and with green 

 eyes. It lays its eggs on the celery leaf, and the young 

 larvae at once burrow into the interior. They are found 

 hovering over the celery plants as early as April, but the 

 majority come out in June. The pale blisters become brown, 

 and inside these diseased spots the white larva may turn 

 to a yellowish-brown puparium. There are several genera- 

 tions in the year. Some puparia are found in the earth, 

 especially during the winter months. The larvae go on 

 working in mild winters as long as the celery is in the 



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