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

SIMPLE SUMMARY: The oriental fruit fly Bactrocera dorsalis Hendel is a highly invasive fruit fly that causes extensive damage to many fruits and vegetables. Irradiation treatment is an economically effective and promising treatment measure. However, treatment efficacy is affected by the presence of low oxygen, i.e., mangoes are treated in modified atmosphere package. In order to investigate the reduced (radioprotective) effects on insects and determine its critical O(2) level, third-instar B. dorsalis larvae were irradiated by X-rays at the doses of 8 to 64 Gy with intervals of 8 Gy. The treatments were conducted under ambient air or low-oxygen atomospheres (0%, 2%, 4%, 6%, 8% O(2) and nitrogen). No adult emergence from treatments at 64 Gy in pure nitrogen or 56 Gy under other atmospheres, resulted in significant difference in tolerance. The results from statistical analyses indicate that differences in tolerance to radiation were significant in 0% and 2% O(2) but insignificant in 4%, 6%, and 8% O(2) environments when compared with radiation in ambient air. Therefore, the critical threshold is an O(2) level of ≥4% and <6%, but a maximum radiation dose of 14 Gy can compensate for the radioprotective effects when the oriental fruit fly is treated in low-oxygen atmospheres. ABSTRACT: Ionizing radiation creates free radicals, the effect of which is enhanced by the presence of oxygen; a low oxygen level produces radioprotective effects for insects compared with irradiation in ambient air. Modified (controlled) atmosphere packaging is used for maintaining quality and shelf-life extension; therefore, treatment efficacy may be affected, and there is a need to determine the critical O(2) levels that may cause radioprotective effects. Late third-instar Bactrocera dorsalis (Hendel) larvae were irradiated in bags filled with ambient or low-oxygen air (0%, 2%, 4%, 6%, 8% O(2)) and were exposed to radiation doses of 8 to 64 Gy with intervals of 8 Gy. Efficacy was measured by the prevention of adult emergence. Dose–response data on mortality (failure of adult emergence) were analyzed via two-way ANOVA (analysis of variance), ANCOVA (analysis of covariance), and probit regression. The difference in radiotolerance was only significant in 0% O(2) atmospheres through two-way ANOVA; therefore, the 95% confidence limits (CLs) of lethal dose ratios at LD(99) were used to determine significant differences between treatments at different O(2) levels. The differences in radiotolerance were significant in 0% and 2% O(2) but insignificant in 4%, 6%, and 8% O(2) environments when compared with radiation in ambient air. The critical threshold of radioprotective effects for late third-instar B. dorsalis larvae is an O(2) level of ≥4% and <6%, but a maximum radiation dose of 14 Gy can compensate for this effect during phytosanitary irradiation treatment.