Onion Maggot

species: Delia (=Hylemya) antiqua common names: onion maggot hosts: onions notes:

Agriculture and Agri-Food Canada Insect Identification Sheet No. 41 March 1981

Onion Maggot

Delia (=Hylemya) antiqua (Meigen)

The onion maggot is a serious pest of onions wherever they are grown in Canada, especially in British Columbia, Ontario and Quebec. It attacks only onions and leeks.

Injury:

In the spring, when the onions are small, the larvae feed by burrowing through lower stems and roots, resulting in wilting and death to the plant. A single larva frequently destroys a dozen or more plants before it matures. When larger onions are attacked, the bulb of the onion is often hollowed out. Though the plant may survive, growth may be distorted or rotting may set in.

Life History:

Onion maggots overwinter in the pupal stage, with adult flies emerging from the middle of May to the end of June. Adults resemble the common housefly but are slightly smaller (6 mm) and pale grey. The elongate white eggs are laid in the soil at the base of onion plants. The creamy white larvae emerge within 1 week, and reach a length of 7 mm when full grown. From the middle of June to the end of July the larvae enter the soil to pupate. The pupae are chestnut brown and resemble grains of wheat. Within a week adult flies emerge. There are two generations in most provinces, or a full first and a partial second. Somearial even a partial third generation is produced in a long mild fall.

Pest Management:

To reduce infestation, all cull onions should be removed from onion fields as onion maggots frequently overwinter in them. For more information contact your provincial Department of Agriculture.

THE FOLLOWING (UNTIL OTHERWISE NOTED) IS FROM: GERBER, H.S. 1983.
MAJOR INSECT AND ALLIED PESTS OF VEGETABLES IN BRITISH COLUMBIA.
MINISTRY OF AGRICULTURE AND FOOD.

Onion Maggot, Delia (=Hylemya) antiqua (Meigen)
A major pest wherever onions are grown in British Columbia. It is specific to onions.

Vegetables Attacked:

Onion

Injury:

Maggots feed on sets, seedlings, transplants, and developing onions. Several small plants may be killed by a single maggot boring into the main stem or bulb. Plants that are killed develop a grey overcast, wilt, turn pale green to yellow, and characteristically remain in place within the row. Established plants are damaged but not usually killed. Maggots enter the base of developing bulbs. Feeding damage causes bulbs to be misshapen and permits the entry of decay organisms and other species of maggots.

Insect:

All life stages are similar in color, size and shape to those of the cabbage maggot (see page 48).

Life History:

There are three generations a year. Pupae overwinter in the soil. Flies emerge from early to mid-May. Eggs are laid in the soil beside the onion plant. Maggots hatch within one week, crawl down the developing bulb, and enter the basal plate. They feed by rasping the plant tissue with a pair of hook-like mouthparts. Maggots mature in two to three weeks and pupate in the soil near the host plant. Flies emerge in about two weeks.

Monitoring:

If a monitoring service is available in your area, it would be advisable to hire it. If not, apply control sprays as indicated in the current Vegetable Production Guide for Commercial Growers. The onion fly resembles other flies so closely, that it is impossible for an untrained person to identify it.

Control:

Control is preventive; treatments must be applied before damage occurs. Against maggots, insecticides are applied and incorporated into the soil prior to planting or seeding; against flies, they are applied at regular intervals to the foliage and soil surface. Timing, rates, and method of insecticide application depend on whether the onions are spring-seeded or transplanted from fall-seeded onions. Culls should be buried or disposed of in a sanitary land fill.