Abstract
Damaged bulbs left in the field following harvest were the major food source for overwintering populations of Delia antiqua (Meigen). Numbers of pupae overwintering in the field soil ranged from 0.06 million (boiler onions) to 0.67 million (bulb onions) per ha. Flies emerged from at least 95% of these pupae in the spring. Approximately 400 flies (about 0.1% of the total spring population) emerged from piles of onions culled from each ha of harvested crop. Unfavorable conditions within cull piles and the inability of larvae to establish on undamaged volunteer plants in the spring indicate that neither of these sites are important sources of D. antiqua infestations.