==Celery Fly.==—­The apparent blisters in Celery leaves are spots deficient of leaf-green, which the larva of the Celery Fly has eaten.  Dusting newly-planted Celery with lime or soot may do something to prevent the fly from laying its eggs, but the most certain preventive is to boil half a pound of coal tar in one gallon of water for twenty minutes, add fifty gallons of clear water, and syringe the plants about noon once or twice from the middle to the end of June.  When once the grub has made a home, it should be crushed by pinching the leaf between the finger and thumb, or the injured portions of the leaves should be cut out and burned.  In doing this it must always be remembered that the leaves are as much needed by the plant as the roots, and every leaf removed tends to diminish the vigour of the plant.  Our illustration shows the Celery Fly (formerly known as =Tephritis onopordinis=, but now called =Acidia heraclei=) natural size and magnified.  This fly is also destructive to the leaves of Parsnips, and is named =onopordinis= from its habit of frequenting the Cotton Thistle (=Onopordon Acanthium=).  The larva is white to very pale green, the fly is shining tawny.  An Ichneumon Fly detects the larva of the Celery Fly in the Celery and Parsnip leaves, and lays its eggs in the body of the larva.  These parasites, named =Alysia apii=, assist in reducing the numbers of the Celery Fly.

[Illustration:  Celery fly and larva =Acidia heraclei=]

All Celery refuse should be destroyed by fire.  Infested ground may, if suitable, be trenched, bringing the subsoil to the surface and burying the top soil containing the pupae.  Frequent rough digging and the exposure of fresh surfaces to be searched by birds will also do something to abate the number of this pest.  But in bad cases it will be necessary to resort to gas-lime, which poisons the pupae and eventually benefits the soil, although in the season immediately following its use crops may be less satisfactory than usual.

==Onion Fly.==—­Onions are frequently attacked by the larvae of the Onion Fly, and in some instances the entire crop is destroyed.  Our illustration shows the natural size of the fly and maggot, with magnified representations of both.  The fly lays six to eight eggs on an Onion plant, generally just above the ground.  These eggs hatch in from five to seven days, according to the temperature, and the maggots at once burrow into the Onion.  The result is soon visible in the discoloration of the leaves which turn yellow and begin to decay.  Several generations of the insect, the scientific name of which is =Phorbia cepetorum=, appear in the course of a single season.  A close ally is the Cabbage Root Fly (=P. brassicae=), the destroyer of Cabbage roots.

[Illustration:  Onion fly and larva =Phorbia cepetorum=]

Among the numerous methods of preventing attack and of destroying the grubs the following are worth attention:—­