Low oxygen atmosphere enhances post-irradiation survival of Trichoplusia ni (Lepidoptera: Noctuidae)

Authors: LOPEZ-MARTINEZ, GIANCARLO - University Of Florida; Meagher, Robert - Rob; JEFFERS, LAURA - Animal And Plant Health Inspection Service (APHIS); BAILEY, WOODWARD - Animal And Plant Health Inspection Service (APHIS); HAHN, DANIEL - University Of Florida

Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2016
Publication Date: 10/3/2016
Citation: Lopez-Martinez, G., Meagher Jr, R.L., Jeffers, L., Bailey, W., Hahn, D. 2016. Low oxygen atmosphere enhances post-irradiation survival of Trichoplusia ni (Lepidoptera: Noctuidae). Florida Entomologist. 99(2):24-33.

Interpretive Summary: Ionizing radiation is a phytosanitary treatment to control risks associated with trade of fresh fruits and vegetables. Commodity producers wish to irradiate fresh product stored in modified atmosphere packaging to increase shelf life and delay ripening. However, irradiating insects in anoxia increases radiation tolerance and regulatory agencies are concerned that modified atmosphere packaging will decrease the efficacy of radiation doses recommended to neutralize insects. A study was conducted by a scientist from USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology, Gainesville, Florida, in collaboration with scientists from the University of Florida and USDA-APHIS to assess the impact of lowered atmospheric oxygen on the radiation tolerance of the cabbage looper moth, a common leaf-eating pest. The results show that irradiation of cabbage looper in anoxic atmospheres increases radiation tolerance compared to irradiation in normal atmospheres. Of the 3 stages irradiated, the last instar larvae were most susceptible to irradiation, followed by pupae, with late pupae being the most tolerant stage. It was found that a moderate dose of irradiation coupled with anoxia will kill most but not all larvae. It is concluded that a more refined protocol for anoxia/irradiation is needed before it can be used in a commercial setting.

Technical Abstract: 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 F1 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.