Delia spp. (Cabbage Maggot)
The Delia Maggot - cabbage maggot (Delia radicum) is a very damaging insect to cool-season plants like cabbage, broccoli, cauliflower, Brussels sprouts, radishes, rutabagas, turnips, etc. The first signs of maggot damage are the wilting of leaves. At this point the roots should be checked for maggots.
The Delia Maggot emerges in cool weather over a period of to 2-3 weeks. This exposes transplants and seedlings to a prolonged egg-laying period (up to 30 days) and there are usually 3 to 4 generations per year. The flies first emerge and mate during May after they have overwintered in the soil in the pupa stage. Once the white maggots emerge they move to the root zone for feeding, either damaging or destroying the root system. In 20-30 days they have matured and are ready to pupate again. After 10-14 days the adult files emerge.
Due to the variation in length of the developmental stages and the emergence of adults in the spring Delia maggots can be present for much of the growing season. The high temperatures in July and August and diseases reduce the populations. However in September and October more maggot damage on fall crops will occur due to the cooler weather.
Information was excerpted from the University of Maine.