Cabbage Maggot

species: Delia (=Hylemya) brassicae
common names: cabbage maggot
hosts: cole crops, cruciferous weeds
notes:

Agriculture and Agri-Food Canada Insect Identification Sheet No. 31 1977 Cabbage Maggot Delia (=Hylemya) brassicae (Bouche) The cabbage maggot is a destructive pest of cabbage, cauliflower, broccoli, Brussels sprouts, radish and turnip in Canada.

Injury:

The larvae feed on the roots and often leave them riddled with tunnels. The injury to the roots results in stunted growth or death of the plants. Severe wilting of the leaves, particularly during dry weather, is the first sign of attack.

Life Cycle:

The cabbage maggot overwinters in the pupal stage and in late May or in June the adult flies begin to emerge. They are gray with black stripes on the thorax and, although smaller, resemble houseflies. Their life span is 2 to 5 weeks during which the females mate and lay their eggs. The small, white eggs are laid in the soil near the plants and hatch in 3 to 7 days. After hatching, the legless, white larvae burrow down to the plant roots to feed on them for 3 to 4 weeks. When fully grown, about 6 mm (1/2 in.) long, the larvae usually move away from the roots and form brownish protective cases, or, in the soil at depths of 5 to 1 3 cm (2 to 5 in.). If the soil is very dry, they may remain in the roots to pupate. After pupation, 2 to 3 weeks are required before flies emerge from the puparia and work their way up out of the soil to produce a new generation. In Canada, the pest usually produces two or more generations annually. Maggots that form puparia late in the summer or in the fall remain in the pupal stage for the winter, with the flies emerging the following spring.

Pest Management:

Follow provincial recommendations for control of the cabbage maggot.

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.

Cabbage Maggot, Delia (=Hylemya) brassicae (Bouche) The most common species of root maggot in Southern British Columbia it is a particularly serious pest of cabbage, cauliflower, radish, and rutabaga. It only attacks species in the mustard or cabbage family.

Vegetables Attacked:

Cole crops: Broccoli, Cauliflower, Radish, Brussels Sprouts, Kale, Rutabaga, Cabbage, Kohlrabi, Turnip

Injury:

Larvae or maggots feed by tunneling in the roots. Plants may be killed, weakened, or stunted and yields reduced. Plants that are killed, wilt, have a gray overcast, and remain in place in the row unlike those severed at ground level by cutworms. A small amount of tunneling in rutabaga or radish lowers the grade or renders the crop unmarketable. Feeding damage by the cabbage maggot causes roots to be misshapen and allows the entry of decay organisms and other species of maggots.

Insect:

The adult is a two-winged, ash-grey fly with black stripes on the mid-section. It is half the size of a housefly, but has longer legs. Larvae are white, legless maggots. They are wedge-shaped with dark feeding-hooks at the pointed front end. The pupae are 6 mm long, oval, hard shelled and dark brown.

Life History:

There are two to three generations a year. Pupae overwinter in the soil near the roots of the host plant. Adult flies emerge in the spring and crawl to the surface. They fly close to the ground near host plants and lay elliptical white eggs on the stems or in nearby crevices in the soil. Eggs hatch in three to seven days. Maggots enter the roots and feed by rasping the plant tissue with a pair of hook-like mouthparts.
They mature in three to four weeks and Pupate. Flies emerge in two to three weeks.

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. In some areas the cabbage maggot is resistant to some organophosphate insecticides.