Onion Maggot
Delia antiqua
Soil Pests & Nematodes High Risk 6-8 mm (adults); up to 8 mm (larvae)
📖 Description
The onion maggot is a serious pest of allium crops throughout temperate regions of the Northern Hemisphere. The larvae tunnel into bulbs, feeding on the fleshy scales and introducing bacteria that cause soft rot. First-generation larvae are the most damaging, as they attack young seedlings and can destroy entire plantings. The pest is particularly troublesome in areas with a history of continuous allium production, as populations build up in the soil over successive seasons. Onion maggots are attracted to the volatile compounds released by damaged onion tissue, making thinned or injured plants especially vulnerable to attack.
⚠️ Symptoms to watch for
- Wilting and yellowing of seedling onion plants,Maggots found inside bulbs and at the root plate,Rotting bulbs with foul odor from secondary bacterial infection,Seedling death in early spring plantings,Lodging (falling over) of affected plants
🩹 Treatment
- Cover seedlings with floating row covers immediately after planting (organic),Apply beneficial nematodes (Steinernema feltiae) to soil for larval control (organic),Use chlorpyrifos soil drench at planting in areas with chronic infestations (chemical),Apply diazinon granules at planting time (chemical)
🌿 Organic treatments
- Cover seedlings with floating row covers immediately after planting,Apply beneficial nematodes (Steinernema feltiae) to soil for larval control
🧪 Chemical treatments
- Use chlorpyrifos soil drench at planting in areas with chronic infestations,Apply diazinon granules at planting time
🛡️ Prevention
- Rotate allium crops to a different garden area for at least 3 years,Destroy crop residues immediately after harvest to eliminate pupation sites,Use row covers from planting until first generation flight ends,Plant later in the season to avoid first-generation egg-laying
🪴 Affected plants
- Onions,Garlic,Leeks,Shallots
🦋 Natural predators
- Ground Beetles,Rove Beetles,Parasitic Wasps,Birds
🌱 Host plants
- Allium cepa,Allium sativum,Allium porrum,Allium cepa var. aggregatum
🔄 Lifecycle
- Onion maggots produce two to three generations per year depending on latitude.
- They overwinter as brown pupae in the soil near the base of previous host plants.
- First-generation adults emerge in early spring and lay eggs at the base of young allium seedlings.
- Larvae feed for 2-3 weeks before pupating in the soil.
- Second and third generations follow through the summer, with later generations typically less damaging than the first.
- The complete lifecycle takes about 4-6 weeks.
📅 Season
- Early Spring to Fall (first generation most damaging)
🔎 Appearance
- Onion maggot adults are small, grayish flies that resemble houseflies but are slimmer, with longer legs and a more hunched posture.
- They have large reddish-purple eyes and dark stripes on the thorax.
- Larvae are creamy white, legless maggots with a tapered head end and a blunt rear end featuring two dark breathing tubes (posterior spiracles).
- Pupae are brown, oval, and about 5-7 mm long, found in the soil near the base of host plants.
- Eggs are white, elongated, and laid in clusters at the base of the plant or in soil cracks.
💥 Damage level
- High
🔁 Reproduction rate
- Moderate
🗺️ Geographic regions
- North America
- Europe
- Asia
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