Onion Maggots
Delia antiqua or onion fly maggot damage the bullbs of onions, garlic, chives, shallots, leeks and flowering plants.
The onion fly itself has an ash-grey body and resembles a housefly. The male has a longitudinal stripe on the abdomen.
When plants are attacked, the leaves start to turn yellow and the bulbs rot quickly, especially in damp conditions.