A new improved diet, supplemented with fine sand, onion juice and distilled water, prevented diet from hardness and cracking, and resulted in a successful mass rearing of Delia antiqua (Meigen) and Delia platura(Meigen) for the larval development. Optimal dose of $cobalt^{60}$ gamma ray was 3 kilo-rad for sufficient sterilization of pupae of D. antiqua and D. platura. Mature sperms were not found in testes of the treated D. antiqua and D. Platura, but well-developed sperms were observed in normal males. Release of sterile onion flies efficiently lowered the percentage of damaged garlic plants in greenhouse.