The purpose of this research was to determine if ??-irradiation of lepidopteran pupae in oxygen would have a greater effect in either preventing adult emergence or in the successful development of F1 life stages than ??-irradiation of pupae in air. Pupae of the citrus fruit borer, Ecdytolopha aurantiana (Lima) (Lepidoptera: Tortricidae), were irradiated in either 100% oxygen or in normal air. In each experiment, thirty 10 d-old pupae of E. aurantiana in each of 4 replicates were treated with either 0, 100, 200 or 300 Gy of ?? radiation. After irradiation the percent emergence of adults, and the percent viability of F1 eggs and larvae were compared with the corresponding results of irradiation in air. The results showed that irradiation of the pupae in pure oxygen significantly reduced the adult emergence and egg hatch compared to irradiation of the pupae in air. Thus irradiation in oxygen of pupae with 300 Gy completely prevented emerged adults from producing eggs. Therefore, irradiation of E. aurantiana pupae with 300 Gy in oxygen is a viable candidate as a phytosanitary treatment. In contrast, irradiation in air of pupae with 300 Gy resulted in 5% egg hatch, although 100% of these larvae died as first or second instars. Therefore based on the criterion of 100% mortality of F1 larvae, 300 Gy in air can also be considered to be a viable candidate for a phytosanitary treatment. These results indicate that the dose required for (PI) treatment may be reduced by increasing the oxygen gas content in fruit packages or containers.