Allium leaf miner has two generations a year:
- First generation female flies lay eggs on the stems or base of leaves during March and April
- The second generation repeats the process in October to November, this generation is usually the most damaging
The maggots bore into the foliage, stems or bulbs of their host plants and, after a couple of weeks, are fully fed and ready to turn into brown pupae. Pupation takes place mainly within the stems and bulbs during summer and winter but some pupae may end up in the soil, especially where plants have rotted off.