White root maggot, legless, up to 1/3 inch long.
Onion.
Burrows into bulbs.
Northern United States.
Onion maggots overwinter as pupae in the soil. As temperatures rise in early spring pupae mature into adults and emerge from the soil. Females begin to lay eggs in less than two weeks. Females may lay about 200 eggs in less than two weeks in three separate groups. When plants are young eggs are deposited around the base of the onion, but as plants mature and precipitation drops, females deposit eggs directly on the leaves and, bulbs or roots, in cases where mature onions are left to dry in the field. Larvae hatch from the eggs in a couple days and bore into plant tissues. Larvae feed on the onion plant for about 2-3 weeks before pupating in the soil. Three generations occur annually in Virginia.
If applying manure, let it age and mix it throughly into the soil. Rototill ground at least 2 weeks before planting. Plow under crop debris immediatley after harvest to prevent use of plant remnants as overwintering sites. Onion maggot infestations can be prevented by covering the seedbed with cheesecloth or screening placed immediately after seeds are sown. Covering should extend at least 6 inches on either side of the seed row. Individual cones made of screeen can be placed over young plants and can be stacked and set aside for use in subsequent years.
Apply diatomaceous earth to the base of the plants.
Treat with a registered insecticide at planting time.
Notice: Because pesticide labels can change rapidly, you should read the label directions carefully before buying and using any pesticides. Regardless of the information provided here, you should always follow the latest product label when using any pesticide. If you have any doubt, please contact your local Extension agent or pesticide dealer for the latest information on pesticide label changes.
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Prepared by Alexandra Spring and Eric Day (Modified from a publication by the USDA)