Onion maggots (Delia antiqua) can cause severe production losses in onion fields in New York State, with losses reaching levels near 100% in the absence of control measures. Onion growers in New York State apply an organophosphorus insecticide (Lorsban) as a seed drench at planting time, or an insect growth regulator (Trigard) incorporated in the seed pellet, in an effort to control larval feeding damage to onion seedlings from first generation maggots. The effectiveness of soil insecticides is limited to this first generation, and second and third generation onion maggots are not controlled by soil insecticides.