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)

BACKGROUND: Phytosanitary irradiation is a sustainable alternative to
chemical fumigants for disinfesting fresh commodities from insect pests.
However, irradiating insects in modified atmospheres with very low oxygen
(<1 kPa O2) has repeatedly been shown to increase radioprotective
response. Thus, there is a concern that modified atmosphere packaging
could reduce the efficacy of phytosanitary irradiation. One hurdle slowing
the widespread application of phytosanitary irradiation is a lack of
knowledge about how moderate levels of hypoxia relevant to modified
atmosphere packaging of most fresh commodities (3-10 kPa O2) may affect
phytosanitary irradiation treatments. Therefore, we hypothesize that
critical PO2 (Pcrit), the level of oxygen at which an insect’s metabolism
becomes impaired, can be used as a diagnostic biomarker to predict the
induction of a radioprotective response. RESULTS: Using the cabbage looper
Trichoplusia ni (Hübner), we show that there is a substantial increase in
radiation resistance when larvae are irradiated in atmospheres more
hypoxic than their Pcrit (3.3 kPa O2). These data are consistent with our
hypothesis that Pcrit could be used as a diagnostic biomarker for what
levels of hypoxia may induce radioprotective effects that could impact
phytosanitary irradiation treatments. CONCLUSION: We propose that the
relationship between Pcrit and radioprotective effects could allow us to
build a framework for predicting the effects of low-oxygen atmospheres on
the efficacy of phytosanitary irradiation. However, more widespread
studies across pest species are still needed to test the generality of
this idea.