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)

Abstract

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 O 2 ) 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 the modified atmosphere packaging of most fresh commodities (3-10 kPa O 2 ) may affect phytosanitary irradiation treatments. Therefore, we hypothesize that critical PO 2 (P crit ), 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 P crit (3.3 kPa O 2 ). These data are consistent with our hypothesis that P crit 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 P crit 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.

Radioprotective Effects on Late Third-Instar Bactrocera dorsalis (Diptera: Tephritidae) Larvae in Low-Oxygen Atmospheres

“…Since there is a small difference in LD 99 values of 1.1 Gy (1.95% of the radiation doses) between the treatments in 4% and 6% O 2 (Table 3), more precise research is required to reduce the range of critical values, for example, by conducting radiation testing in 4.5% or 5% O 2 atmospheres. Similarly, radioprotective effects have been observed in other fruit insects irradiated at <3-5% O 2 levels, such as A. suspensa [33], C. capitata [34], Z. cucurbitae [13], D. suzukii [35], G. molesta [36], O. nubilalis [37], and T. ni [22,23]. Furthermore, all these results support the APHIS' (Animal and Plant Health Inspection Service, United States Department of Agriculture) changes to administrative requirements, wherein the minimum O 2 level was reduced from 18% to 10% for conducting PI treatments [22,41].…”

“…The third-instar larvae were irradiated in a series of O 2 levels with the same dose to compare the relative tolerance between treatments, and the prevention of adult emergence was selected as the common efficacy criterions [4,9,11,31,32]. Radiation tolerance in insects is modified by the oxygen level and increases in low-oxygen atmospheres; in particular, insects irradiated in very low oxygen (<1% O 2 ) have repeatedly been shown to have an increased radioprotective response [10,23]. In our study, an increased radiotolerance of B. dorsalis in low-oxygen environments (0%, 2%, and 4% O 2 ) was confirmed by comparing mortality rates using two-way ANOVA (Table 1), the estimated minimum doses for 100% mortality by linear regression after ANCOVA (Table 2, Figure 1), and LD 99 by probit analysis ( Table 3, Figures 1 and 2).…”

“…In order to define the critical threshold of radioprotective effects, radiation treatments in a series of oxygen levels should be carried out and the dose-response data subjected to statistical analysis to determine the statistically significant differences in radiotolerance [22,23]. The probit model is commonly used to analyze dose-response data [38,40]; however, the values of the slope obtained in this research (Table 3) are unequal, which means that the regression lines are unparallel, whereas they were parallel when Srimartpirom et al treated B. dorsalis in MAP [11].…”

“…Although reduced effects of radiation have been validated by several studies that conducted radiation treatment in <3-5% O 2 atmospheres, most of them performed comparisons between ambient air and pure nitrogen or MAP, whereas the difference in radiation effects was insignificant [23]. In addition, the PI treatment efficacy was not reduced when fruit flies were treated under hypoxia [12].…”

“…In addition, the PI treatment efficacy was not reduced when fruit flies were treated under hypoxia [12]. Therefore, more research is required to determine the critical O 2 levels that may cause radioprotective effects for insects and at which point the efficacy of the recommended doses for commercial PI treatment may decrease when conducting treatments in low-oxygen environments [21][22][23]. Thus, the objective of this research was to investigate the critical O 2 level (threshold value) that may induce radioprotective effects for late third-instar B. dorsalis larvae and to estimate the radiation dose that compensates for this reduced efficacy.…”