Synergistic integration of Citrus aurantium essential oil and gamma radiation: A strategy for optimizing radiation in the effective control of Sitophilus oryzae and Tribolium castaneum

The management of stored-grain insect pests, Sitophilus oryzae and Tribolium castaneum, can be enhanced through combined gamma radiation and plant-derived essential oils. This study assesses the potential of Cobalt-60 γ-radiation together with Citrus aurantium essential oil (CAEO) as an alternative to synthetic fumigants. Lethality was assessed for single γ-radiation treatments, applied at 20 doses (100-2000 Gy at 3.98 kGy/h), and CAEO fumigation at five concentrations (16.66-100 µL/L air). Combined effects were evaluated using sublethal CAEO concentrations (S. oryzae: LC₅: 8.87 µL/L air; LC₁₀: 15.40 µL/L air; T. castaneum: LC₅: 6.45 µL/L air; LC₁₀: 15.68 µL/L air) with sublethal γ-radiation doses (S. oryzae: LD₅: 260 Gy; LD₁₀: 305 Gy; T. castaneum: LD₅: 598 Gy; LD₁₀: 710 Gy). After 72 h, mortality rates for S. oryzae following single γ-radiation treatments were 14% (100–500 Gy), 82% (600–1000 Gy), and 100% (1100-2000 Gy), while for T. castaneum, they were 2% (100–500 Gy), 16.4% (600–1000 Gy), 34.8% (1100-1500 Gy), and 84% (1500-2000 Gy). CAEO alone induced 12-50% mortality. Combined treatments significantly increased mortality (66-86% for S. oryzae and 44-58% for T. castaneum), demonstrating synergistic effects and notably reducing the required radiation dose by ~4-fold for S. oryzae and ~3-fold for T. castaneum. For S. oryzae, LD_5(γ) combined with LC_5(CAEO) and LC_10(CAEO) yielded synergism indices of 0.489 and 0.469, while LD_10(γ) combinations produced indices of 0.492 and 0.474. For T. castaneum, LD_5(γ) with LC_5(CAEO) and LC_10(CAEO) resulted in synergism indices of 0.482 and 0.530, and LD_10(γ) yielded 0.560 and 0.567 in combination. The radiation doses in this study remained well below the IAEA’s recommended 1000 Gy threshold for stored-grain pest disinfestation. Combining sublethal radiation doses with CAEO enhanced insect mortality, suggesting that lower radiation doses could be used effectively, potentially reducing concerns about high-dose irradiation and offering a sustainable alternative to synthetic fumigants for managing stored-grain pests.