Agriculture and Agri-Food Canada Insect Identification Sheet No.
41 March 1981
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.
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.
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.
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.
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.
All life stages
are similar in color, size and shape to those of the cabbage
maggot (see page 48).
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.
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.
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.