Onion Fly
Delia antiqua
Onion Fly
The Onion Fly is ash-grey and looks a lot like a common housefly. The larvae are most problematic in gardens and allotments because they bore the bulbs of onions, garlic and leek. If you find an infestation, it should be removed and disposed of as soon as possible to prevent another generation from hatching the following year. Wilting and yellow foliage is one of the main symptoms.
Traits

Onions, garlic, shallots and leeks may be damaged and made inedible as a result of an onion fly infestation.
Appearance
The onion fly is ash-grey in colour and looks a lot like a common house fly. The legs are a dark black colour while their wings are transparent.
The females are slightly different and lack the longitudinal stripe that the males have down their abdomen.
The eggs are white and laid in groups on the shoots, leaves or bulb of the plant.
Larvae is also white and cylindrical in shape.
Symptoms
Leaves turn yellow
Wilting
Rotten bulbs
Hollowed out bulbs
Plant death
Activity
Diurnal
Personality
Order
Diptera
Family
Anthomyiidae
Metamorphosis
Complete
Distribution
North America, Western Europe, Russia, Central Asia, China, Japan and Korea
Biological treatment
You can buy insect proof netting that will protect any of the flies getting to the plant, preventing them to lay their eggs.
Chemical treatment
You can use insecticides on your soil to provide effective control, this will kill any living larvae
Attracts
Bulbous plants