Onion Maggot

Diptera: Anthomyiidae
(Delia antiqua)


Onion root maggot flies are hump-backed gray-brown flies, about 1/3 inches long resembling small house flies. Magots are creamy-white, legless, and only 0.4 inches. The onion maggot is the most damaging insect pest of onions throughout the northern areas and if not controlled, it can prevent the production of the marketable crop.

Life Cycle

Onion maggots have four life stages: egg, larva (maggot), pupa, and adult (fly). Onion maggots spend the winter as small brown pupae in the soil. In spring, the pupae develop into adults and mate when they are 6 days old. Females lay up to 200 eggs during their lifetime. Female flies seek out onions to lay eggs around the base of the onion seedlings. Maggots, after emerging, crawl beneath the leaf sheath and enter the bulb. They can attack the onion at any stage of development and feed within the plant for about two to three weeks. When the maggot becomes fully grown it leaves the onion and pupates in the soil. Onion maggots have about three generations each year.

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Although onion maggots are an early-season pest of onion plants, they can cause damage throughout the season. Onion plants are most vulnerable to the first generation of onion maggot during the seedling stage, and larval feeding may kill the seedlings. The second generation of onion maggot feeds on the stem and developing bulb that causes wilted rotten foliage and misshapen bulb which makes the crop unsuitable for the market. At the end of the season, the third-generation onion maggot feeding can lead to storage rots.

Biological Control