Do modified atmospheres used in commodity packaging alter the efficacy of irradiation as a phytosanitary treatment?

Irradiation as a phytosanitary treatment (IPT) prevents the spread of invasive pest insects in agricultural products. A current barrier to IPT is development of generic radiation doses that effectively kill or sterilize all pests across commodities. 400 Gy is a USDA-approved generic dose that can be applied to all insects except Lepidoptera pupae and adults, and 150 Gy has been approved for all Tephritid fruit flies. Development of additional generic doses <400 Gy will contribute to preserving commodity quality while helping to prevent irradiators with high dose uniformity ratios (DUR) from exceeding the current FDA limit of 1000 Gy for IPT. Many commodities are transported in modified atmospheres with low oxygen content. Irradiation in low oxygen may affect treatment efficacy, a potential challenge for developing generic irradiation doses. We tested the effects of low oxygen on irradiation treatments of the cabbage looper, Trichoplusia ni. We irradiated larvae, early pupae, and pharate adults (late pupae) at 50, 100, 150, 200, 400, 600, and 800 Gy under both anoxic and normoxic atmospheres. Anoxia increased survivorship and adult emergence for all tested life stages and irradiation doses.  However, for both normoxic and anoxic treatments, the fertility at high doses of radiation (>400 Gy) was negligible. Future work will involve irradiation in atmospheres with a range of reduced oxygen (0-20 kPa) and increased carbon dioxide (0-10 kPa) to mimic the range of controlled and modified atmospheres used in commodity packaging.