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To clarify tissues susceptible to chill injuries in the pupae of the onion maggot, Delia antiqua (Diptera : Anthomyiidae), 5 d old non-diapausing pupae (ND5) were subjected to a non-freezing temperature of -20℃, with or without prior acclimation at 5℃. Cold acclimation of pupae for 8 d or longer substantially decreased the mortality after exposure to -20℃ for 5 d. Analysis of the morphology of dead pupae suggested that they died at two discrete developmental stages : after formation of the adult morphology (type 1), and at a stage indistinguishable from ND5 in appearance (type 2). The two types of death were differentially induced by changing the period of -20℃ treatment. A majority of pupae exhibited type 1 death after a 2 d treatment, whereas type 2 death was predominant after a 12 d treatment. Regarding the type 1 death, pharate adults appeared to have died because they failed to emerge from the puparial case. Possibly, the neuromuscular system was impaired by the short term chilling at -20℃. On the other hand, the Malpighian tubules were seriously damaged by long term chilling at -20℃, and this is thought to be the cause of type 2 death.