|Crop Knowledge Master|
Delia platura (Meigen)
|Seed corn Maggot|
Jayma L. Martin Kessing, Educational Specialist
Ronald F. L. Mau, Extension Specialist
Department of Entomology
Seedcorn maggots can be serious pests of sown seeds of beans and maize. Additional crops attacked include cabbage, corn, cucumber, green beans, lettuce, onion, peas, seed potatoes, spinach and other crucifers.
This pest is of European origin but is now found throughout most of southern Canada and the mainland US. It is common throughout Hawaii from sea level to 6,500 feet (Hardy, 1981).
Damage is usually caused in the spring when the larvae or maggots burrow into seeds or seedlings. Larvae begin feeding on germinating seeds or organic matter soon after hatching. Partially decayed seeds, injured seeds, or poorly healed potato pieces are favorite foods. Larvae feed within and destroy the seed. Failure of seed germination or seedling emergence is usually the first sign of infestation.
Attacked beans that sprout often show a "Bald-headed" condition (a plant without primary leaves) or severely damaged primary leaves. This results in stunted plants, deformed beans and reduced yields.
Corn seedlings damaged by this pest are weak and sickly. Typical symptoms are curling, drying, or dead leaves.
Seed potatoes are often attacked if they are bruised, decaying, or diseased. Damage to these fields usually covers large areas and occasionally most of the field. When there is heavy feeding of maggots, replanting may be necessary.
Development of seedcorn maggots from egg to adult occurs in 21-40 days. Depending on climatic conditions, there are 1-5 generations per year (Higley & Pedigo, 1984).
Eggs are deposited close to seeds in soil where there is abundant organic matter, seeds, or plant seedlings. Recently worked soil tends to be favored for egg deposition. Adult females lay an average of 100 eggs over a 3-4 week period. Eggs are elongate, pearly white, with a reticulate pattern. Under normal field conditions, eggs hatch in 2-4 days.
Larvae are small maggots, yellowish white to dirty yellow, legless, and measuring approximately 1/5 inch in length and 1/25 inch in girth in their later stages. Seedcorn maggots have three larval stages. Larval development is completed in 12-16 days.
Mature larvae pupate in the first 2-3 inches of soil a short distance away from the host plant. Pupae are tan to brown and less than 1/4 inch long. They are approximately three times as long as wide. The pupal stage lasts from 7-20 days, depending on temperature.
The grayish brown adult flies are about 1/5 inch long and are often mistaken for small houseflies. Adults may live for 4-10 weeks.
Young larvae are active after emergence. Although occasionally found alone, they usually occur in masses of up to 100 larvae. Feeding begins as soon as a food source is found.
Adults feed upon the nectar of flowers of a number of cultivated and wild plants. Adults are active in the mid-morning, especially when temperatures are between 60û-85ûF. They are inactive at night. Strong winds and rain reduce adult activity. The fly may frequently be seen hovering over plants upon whose flowers they feed on and other objects. Their flight pattern is a series of hovering and darting in different directions. They are attracted to odors from alcohols and sweet, fermenting substances (Reid, 1940).
The greatest damage occurs in cool, wet seasons and in soils containing large amounts of organic matter.
A preventive measure against seed corn maggot infestation is to plant when the soil and weather promotes rapid germination. Planting in highly organic soils, wet soils, or during wet weather periods should be avoided whenever possible as this often leads to increased problems. If using manure, let it age and incorporate it thoroughly into the soil. Severely damaged stands may be reseeded with little danger of reinfestation.
Dragging a chain behind the planter during seeding removes the seed row moisture gradient that attracts oviposition by adult flies. This practice significantly reduces seedcorn maggot damage.
Sanitation practices such as removal of flowering weeds from outlying areas to eliminate nearby food sources for adult flies and removal of sweet smelling substances decreases the attractiveness of an area to these flies. However, this action also reduces nectar sources for beneficial insects.
Because much of its life cycle is passed protected underground, seedcorn maggots do not appear to have a great number of natural enemies (Reid, 1940). Isolated incidences of predation by spiders and birds upon adults, and fungus diseases on the larvae have been reported. However, none of these predators are considered significant in controlling seedcorn maggot populations.
The best way to prevent damage to potatoes is to plant well suberized or healed potato seed pieces. Areas and equipment used for cutting and storing seed pieces should be disinfected and free from damaging bacteria and diseases.
Preventive treatments with insecticides is the only effective way of controlling these maggots in most seeds. Either a granular or seed treatment may be used. Seed treatment is one of the least expensive and most effective treatments for control of seedcorn maggot. The use of some fungicides has reduced seed piece damage and subsequent maggot damage.
Brooks, A. R. 1951. Identification of the Root Maggots (Diptera: Anthomyiidae) Attacking Cruciferous Garden Crops in Canada, with Notes on Biology and Control. Can. Entomol. 83(5): 109-120.
Flint, M. L. 1985. Seedcorn Maggot, Hylema platura. pp. 36. In Integrated Management for Cole Crops and Lettuce. University of California Publication 3307. 112 pages.
Hardy, D. E. 1981. Hylema (Delia) platura (Meig.) pp. 36-38. In Insects of Hawaii. A Manual of the Insects of the Hawaiian Islands, Including Enumeration of the species and Notes on Their Origin, Distribution, Hosts, Parasites, etc. Volume 14, Diptera: Cyclorrhapha IV, series schizophora, section calyptratae. The University Press of Hawaii. Honolulu. 491 pages.
Higley, L. G. and L. P. Pedigo. 1984. Seedcorn Maggot (Diptera: Anthomyiidae) Population Biology and Aestivation in Central Iowa. Environmental Entomology. 13(5):1436-1442.
Hill, D. S. 1983. Delia platura (Meig.). pp. 402. In Agricultural Insect Pests of the Tropics and Their Control. 2nd Edition. Cambridge University Press. Cambridge, London, New York, New Rochelle, Melbourne, Sydney. 746 pages.
Reid, W. J. 1940. Technical Bulletin No. 723. Biology of the Seed-Corn Maggot in the Coastal Plain of the South Atlantic States. United States Department of Agriculture Washington, DC.
Retan, A. E. 1983. Extension Bulletin 1225. Seedcorn Maggot. College of Agriculture and Home Economics, Washington State University, Pullman.