In Manitoba, onion losses from maggot infestations have generally not been economically significant over the last decade. The onion maggot overwinters in Manitoba soil in the pupal stage.
Pupae are brown, oval and slightly larger than a grain of wheat.
When the weather warms up in the spring, pupae develop into adults, which emerge in late May to early June. Adult - These greyish flies can be seen in dandelions along field borders and resemble common house flies. The main difference is that the onion maggot has larger legs and a narrower abdomen. Adult flies can mate at 6 days old and eggs are laid three to four days later. The females, which are larger then males, have a life span of 30 days.