The onion fly (Delia antiqua) is a major pest that infests onions, shallots, and leeks. Currently not present in Australia, its introduction could severely impact the onion industry. Strong biosecurity measures are crucial for preventing its entry and establishment.

The adult fly is mobile during egg-laying, while maggots and pupae can overwinter in hosts and spread via contaminated soil or infested plants. Early detection is crucial, as once the fly infests the bulb, no treatments can resolve the issue.

This fact sheet provides an overview of the effects of onion fly infestation, its spread and identification.