Onion maggot

Adults of Delia species are small gray flies that are somewhat smaller than house flies. When at rest, they keep their wings folded one over the other. Larvae are creamy white, legless maggots about 0.4 inch (10 mm) long. Microscopic examination is required to distinguish between species. The flies lay eggs in the soil surface near the germinating plants. Larvae feed on the developing seedling and, in the case of the onion maggot, on the expanding bulb. Mature larvae pupate in the soil. There are several generations per year. Maggots prefer soils heavy in organic matter where they can survive and move to seeds. Seed corn maggots occur throughout California garlic and onion production areas. Onion maggots are more restricted to cooler coastal climates. Maggots are primarily a pest of onions and do not generally cause economic damage to garlic.