Low oxygen atmosphere enhances post-irradiation survival of Trichoplusia ni

Phytosanitary irradiation (PI) is increasingly being used for disinfesting fresh commodities from insect pests of quarantine concern. The development of generic doses of irradiation that can be applied to broadly control all pests within a particular family, order, or even all insects across commodities and packaging types could facilitate greater use of PI. Many commodities are stored in controlled or modified atmospheres that are low in oxygen to preserve commodity quality and extend shelf life, but low-oxygen environments have been shown to affect radiotolerance in some insects and more work is needed to understand the impact of this oxygen-effect on radiotolerance for both the development of generic doses and to increase the acceptance of irradiation as a treatment by the fresh commodity industry. Here we show that irradiation of cabbage looper, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae), in anoxic atmospheres (0 kPa aPO2) increases radiotolerance compared to irradiation in normoxic atmospheres (21 kPa aPO2) last instar larvae, true pupae and mature pupae (pharate adults) when considering the emergence of healthy-looking, viable adults as the critical metric. Of the 3 stages irradiated, the last instar larvae were most susceptible to irradiation, followed by pupae, with pharate adults 24-48 h prior to emergence (sometimes referred to as late pupae) being the most tolerant stage. When pharate adults were irradiated in anoxia, healthy-looking adults emerged at absorbed doses of 784-789 Gy whereas no healthy-looking adults emerged at the same doses in normoxia. Effects of anoxia on reproduction of irradiated female pharate adults were subtle. A few F^sub 1^ larvae hatched at doses estimated to be 585-591 Gy, suggesting that more work is needed to determine whether 400 Gy is an adequate generic dose to control late pupae of T. ni.