Effects of Low-Oxygen Environments on the Radiation Tolerance of the Cabbage Looper Moth (Lepidoptera: Noctuidae)

Abstract

Ionizing radiation is used as a phytosanitary treatment to mitigate risks from invasive species associated with trade of fresh fruits and vegetables. Commodity producers prefer to irradiate fresh product stored in modified atmosphere packaging that increases shelf life and delays ripening. However, irradiating insects in low oxygen may increase radiation tolerance, and regulatory agencies are concerned modified atmosphere packaging will decrease efficacy of radiation doses. Here, we examined how irradiation in a series of oxygen conditions (0.1-20.9 kPa O2) alters radiotolerance of larvae and pupae of a model lepidopteran Trichoplusia ni (Hubner) (Diptera: Noctuidae). Irradiating in severe hypoxia (0.1 kPa O2) increased radiation tolerance of insects compared with irradiating in atmospheric oxygen (20.9 kPa O2). Our data show irradiating pharate adult pupae at 600 Gy in moderately severe hypoxia (5 kPa O2) increased adult emergence compared with irradiation in atmospheric oxygen (20.9 kPa O2). Our data also show that in one of the three temporal replicates, irradiating T. ni larvae in moderately severe hypoxia (5 kPa O2) can also increase radiotolerance at an intermediate radiation dose of 100 Gy compared with irradiating in atmospheric oxygen conditions, but not at higher or lower doses. We discuss implications of our results in this model insect for the current generic doses for phytosanitary irradiation, including the recently proposed 250 Gy generic dose for lepidioptera larvae, and temporary restriction on irradiating commodities in modified atmosphere packaging that reduces the atmosphere to < 18 kPa O2.

Hypoxic environment protects cowpea bruchid (Callosobruchus maculatus) from electron beam irradiation damage

“…(B)). Such priming effect of pre‐hypoxia for better withstanding of incoming stresses have also been reported in other insects, including apple maggot, oriental fruit moth, Angoumois grain moth, Indian meal moth and cabbage looper …”

Critical PO2 as a diagnostic biomarker for the effects of low‐oxygen modified and controlled atmospheres on phytosanitary irradiation treatments in the cabbage looper Trichoplusia ni (Hübner)

“…They found that at an intermediate dose of 100 Gy cabbage looper larvae irradiated in <0.1 kPa O 2 had ~82–85% survival to adulthood, larvae irradiated at 5 kPa O 2 had ~20–25% survival to adulthood, and those irradiated at 10, 15, and 21 kPa O 2 (normoxia) did not survive to adulthood. Thus, moderate hypoxia at 5 kPa O 2 had a small radioprotective effect that was only a fraction of the radioprotective effect observed at <0.1 kPa O 2 . When treated at the higher radiation dose of 200 Gy all cabbage looper larvae irradiated in atmospheres of 5–21 kPa died, but there was still ~15–20% survival to adulthood in caterpillars irradiated at <0.1 kPa O 2 .…”

“…Thus, moderate hypoxia at 5 kPa O 2 had a small radioprotective effect that was only a fraction of the radioprotective effect observed at <0.1 kPa O 2 . When treated at the higher radiation dose of 200 Gy all cabbage looper larvae irradiated in atmospheres of 5–21 kPa died, but there was still ~15–20% survival to adulthood in caterpillars irradiated at <0.1 kPa O 2 . Given that only four studies have been published on irradiation in atmospheres with intermediate levels of hypoxia (2–15 kPa O 2 ), more work is clearly needed to determine the extent to which modified atmosphere packaging may alter the efficacy of phytosanitary irradiation treatments, as well as the levels of oxygen at which radioprotective effects may be induced.…”

“…However, this combination of phytosanitary irradiation with low‐oxygen modified atmosphere packaging is of concern to regulators because severe hypoxia (<1 kPa O 2 ) is known to increase insect radioprotective responses and decrease radiation‐induced mortality in a wide range of insects . For example, survival of the cabbage looper moth Trichoplusia ni (Hübner) was increased from 0% adult emergence when last‐instar caterpillars were irradiated at 100 Gy in normoxia (the partial pressure of O 2 in ambient normal air at sea level is 20.9 kPa) to more than 80% adult emergence when caterpillars were irradiated at the same dose in extreme hypoxia <0.1 kPa O 2 …”

“…However, because both oxygen and carbon dioxide levels were altered by the commercial modified atmosphere packaging bags in the three studies described above, the relative contributions of low oxygen levels versus high carbon dioxide levels to changes in susceptibility to radiation are unclear. Condon et al . exposed last‐instar cabbage looper caterpillars to a range of controlled hypoxic environments including <0.1, 5, 10, 15, and 21 kPa O 2 (normoxia) prior to and during irradiation at a range of doses from 0 to 200 Gy, while keeping CO 2 levels less than 2 kPa over the trials.…”