Egg - Each white elongate egg has a rough surface and is about 1 mm in length.
Larva - This 12-segmented, white to yellow-white maggot is 5 to 7 mm long when mature. It is legless and tough skinned with a sharply pointed head and a rounded tail.
Pupa - The last larval skin hardens to form a puparium (about 5 mm long) in which the pupa develops. The ivory puparium gradually turns reddish-brown as the pupa matures.
Host Plants - Although it feeds primarily on decaying organic matter, the seedcorn maggot infests roots and/or seeds of over 47 kinds of plants. In North Carolina, it is a pest of bean, pea, cucumber, melons, onion, corn, pepper, potato, and other vegetable crops.
Damage - Seedcorn maggots damage newly planted seeds by feeding on seed contents often leaving empty shells and resulting in poor germination. Seedlings which do emerge are tall and spindly with few leaves. They rarely mature or mature late because of poor seed quality. Occasionally, seedcorn maggots tunnel in seedling stems. Either type of feeding allows entry of disease-causing organisms.
Life History - In North Carolina, all stages of the seedcorn maggot can be found throughout the winter. Further north, however, these insects overwinter in the soil as pupae. Adult flies emerge from puparia at night or early in the morning and push themselves up to the soil surface. For a variable length of time, adults feed on nectar and honeydew. At the end of this period, each fertilized female begins laying an average of 270 eggs, singly or in small clusters, in moist soil. Freshly distributed soil, fields with decaying seed or crop remnants, and/or organically fertilized soils are all attractive to ovipositing female flies.
Eggs hatch in 7 to 9 days depending on temperature. Newly hatched larvae tunnel in seeds or other decaying vegetable matter. Maggots remain active at temperatures as low as 4.4 degrees C (40 F). They develop through three larval stages. After feeding for 1 to 3 weeks, the larvae burrow as deep as 18 cm in the soil to pupate. Pupation may last 7 to 26 days or all winter.
In the eastern U.S., three to five generations of seedcorn maggots develop each year. Generations which occur during spring and fall are the most abundant and destructive. During summer, only a limited number of adults survive.
Combination fungicide-insecticide seed treatments or soil-applied insecticides can be used to prevent seedcorn maggot damage. For up-to-date recommendations, consult the current North Carolina Agricultural Chemicals Manual.
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