There are many species of leaf miner flies in the UK, and they can affect a wide range of vegetable and flowering plants, both indoors and out.
For example: Aquilegia, Chrysanthemums, Lilac, Tomatoes and Sweet Peppers to name but a few.
The adults are small, dark-coloured flies around 6mm (¼")long, some have yellow markings, and they emerge in April to late May, mate, and commence egg laying, on or into the upper or lower surfaces of leaves and hatch about a week later.
Second generation mines occur in July, with adult emergence in August.
Adult Leaf Miner
Larvae are grubs about 12mm (½")long, usually white in colour, and feed on the tissue between the leaf surfaces.
These feed in two stages; the sap feeding stage, and the tissue feeding stage.
In the sap feeding stage the 12mm (½")long white larvae feed just above the lower leaf surface.
Leaf Miner larvae
In the tissue feeding stage they begin feeding just below the upper leaf surface,this creates the distinctive mined trails across the leaf surface.
As the larvae grow the mined trails become wider.
Larvae feed for two to three weeks before pupating.
Typical leaf damage
Pupation of the 1st generation occurs in June, followed shortly by the emergence of the adult fly.
Third generation larvae, present by mid-August, pupate in the mines and overwinter, emerging the following spring.
Generations may overlap due to the extended period of egg laying and long larval development.
Spraying with BHC will keep it under control, or by using the parasitoid wasp diglyphus isaea.
This tiny wasp stings the leaf miner while it is its mining and paralyses it.