Modified Atmosphere Does Not Reduce the Efficacy of Phytosanitary Irradiation Doses Recommended for Tephritid Fruit Flies

Abstract

Phytosanitary irradiation (PI) has been successfully used to disinfest fresh commodities and facilitate international agricultural trade. Critical aspects that may reduce PI efficacy must be considered to ensure the consistency and effectiveness of approved treatment schedules. One factor that can potentially reduce PI efficacy is irradiation under low oxygen conditions. This factor is particularly important because storage and packaging of horticultural commodities under low oxygen levels constitute practices widely used to preserve their quality and extend their shelf life. Hence, international organizations and regulatory agencies have considered the uncertainties regarding the efficacy of PI doses for insects infesting fresh commodities stored under low oxygen levels as a rationale for restricting PI application under modified atmosphere. Our research examines the extent to which low oxygen treatments can reduce the efficacy of phytosanitary irradiation for tephritids naturally infesting fruits. The effects of normoxia (21% O2), hypoxia (~5% O2), and severe hypoxia (< 0.5% O2) on radiation sensitivity of third instars of Anastrepha fraterculus (sensu lato), A. ludens (Loew), Bactrocera dorsalis (Hendel), and Ceratitis capitata (Wiedemann) were evaluated and compared at several gamma radiation doses. Our findings suggest that, compared to normoxia, hypoxic and severe-hypoxic conditioning before and during irradiation can increase adult emergence and contribute to advancement of larval development of tephritid fruit flies only at low radiation doses that are not used as phytosanitary treatments. With phytosanitary irradiation doses approved internationally for several tephritids, low oxygen treatments applied before and during irradiation did not increase the emergence rates of any fruit fly species evaluated, and all treated insects died as coarctate larvae. Thus, the findings of our research support a re-evaluation of restrictions related to phytosanitary irradiation application under modified atmospheres targeting tephritid fruit flies.

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

“…The estimated LD 99.9968 values can be used as the minimum dose for PI treatment if they are validated by large-scale confirmatory tests [32,38], and our LD 99.9968 data (80.6 (76.3-85.6) Gy) ( Table 3) are very close to the values (84.1 (73.6-99.3) Gy) that were estimated and validated by Zhao et al [4]; thus, a maximum radiation dose of 14 Gy can compensate for radioprotective effects during the PI treatment of oriental fruit fly. This explains why no radioprotective effects were observed when a radiation dose of 116 Gy (31.9 to 35.4 Gy higher than the LD 99.9968 estimates) was applied to late third-instar B. dorsalis larvae under severe hypoxia (0.3 ± 0.02% O 2 , 21.6 ± 0.1% CO 2 ) [12].…”

“…Commercial PI treatment in MAP or controlled atmospheres is more complicated [39]. The minimum applied dose should be equal to or higher than the maximum dose in the confirmatory tests; therefore, it is much greater than the LD 99.9968 estimates, and radioprotective effects are not observed as a result [12,21,31]. Moreover, although the treatment efficacy is reduced by low-oxygen atmospheres, it is increased by the presence of CO 2 , low temperature, and the long duration of modified atmosphere treatment after radiation treatment [11,12,32,38].…”

“…Phytosanitary measures, including fumigation, temperature, and irradiation treatments, are currently used for shipped commodities, and the use of phytosanitary irradiation (PI) treatment has increased in recent years due to its advantages over other treatments; as a result, the global volume of different fresh products was approximately 30,000 tons in 2017 [3,4,[7][8][9]. In order to develop treatment schedules and facilitate the application of PI treatment, many kinds of tephritid fruit fly third-instar larvae have been used for conducting radiotolerance and confirmatory studies, such as the oriental fruit fly, B. dorsalis [4,[10][11][12]; the Mediterranean fruit fly, Ceratitis capitata Wiedemann [10,12]; the melon fly, Zeugodacus cucurbitae Coquillett [10,13]; and Z. tau Walker [14]. Currently, the International Plant Protection Convention (IPPC) is discussing draft standards related to irradiation treatment for B. dorsalis, Z. tau, and the genus Anastrepha to formulate international standards, as an annex to International Standard for Phytosanitary Measures (ISPM) No.…”

“…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]. 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].…”

“…In order to develop treatment schedules and facilitate the application of PI treatment, many kinds of tephritid fruit fly third-instar larvae have been used for conducting radiotolerance and confirmatory studies, such as the oriental fruit fly, B . dorsalis [ 4 , 10 , 11 , 12 ]; the Mediterranean fruit fly, Ceratitis capitata Wiedemann [ 10 , 12 ]; the melon fly, Zeugodacus cucurbitae Coquillett [ 10 , 13 ]; and Z. tau Walker [ 14 ]. Currently, the International Plant Protection Convention (IPPC) is discussing draft standards related to irradiation treatment for B .…”