Celery Leaf Mining Fly
Celery Leaf Mining Fly, Celery Fly, Hogweed Picture-Wing Fly
Celery Leaf-Mining Flies look like small, light brown fruitflies. They possess a yellow-tan thorax and are only 5mm. Adults active during winter tend to be darker in appearance, described as almost entirely black. They're attracted to large vegetable gardens, allotments and open countryside, typically where there is a lot of the host plant being grown. They can be a pest of Celery and Parsnip, and most damage is caused by the larvae which communally mine tunnels within vegetable leaves, making crops bitter-tasting.
Their intrusive way of feeding can make vegetables taste bitter.
Adults: Flies are light brown in the summer, but black in the winter. They are only 5mm big. The thorax is a shiny yellow-orange or black. They can be found mating on the host plant leaves during April and May. Larvae: White and maggot-like, they reach up to 8mm. Eggs: Tiny, white and oblong-shaped. Difficult to see with the naked eye.
Blotchy leaf mines in foliage that fade brown and dry out. Brown dried-+out flowers Bitter tasting vegetables. Flies can be spotted mating leaves early spring.
It's suggested to grow plants beneath an insect-proof mesh. It's advised to rotate crops every year, and by doing so, infection by overwintering pupae will be less likely. Pick off any leaves that have been mined or have eggs on them. Likewise, pinch out any infested parts of the plant. Plants should be checked regularly during summer, and deeply infested leaves burnt when growing season terminates to destroy any persisting pupae.
Unfortunately, there are currently no chemical treatments available that will give effective control over this pest.