The essential oils isolated by hydrodistillation from Thuja orientalis unripe fruits exposed to gamma radiation at dose levels of 0, 1, 3, and 5 kGy were analyzed by GC–mass spectrometry (MS) and assessed for their insecticidal activities on Trogoderma granarium Everts. The results showed slight changes were observed in the chemical composition of essential oil. The results showed that irradiated oil treatments induced higher toxicity to larvae of T. granarium than unirradiated oil with LD50 values (41.5, 54.2, and 87.1 μl/larva), and LD90 values (122.8, 207.5, and 314.7 μl/larva) for irradiated oil with 5.0, 3.0, and 1.0 kGy, respectively compared with unirradiated oil (LD50 = 153.8 μl/larva) and (LD90 = 622.8 μl/larva) by contact method. The same trend was obtained in the fumigant assay, the irradiated oil treatments with 3.0 and 5.0 kGy increased the toxicity to larvae of T. granarium than unirradiated oil with LC50 values were 280.7 and 183.6 μl/L, and LC90 values were 1171.6 and 687.4 μl/L, respectively compared with unirradiated oil (LC50 = 449.4 μl/L) and (LC90 = 1656.1 μl/L). The results showed also, that at 0.063 and 0.126 μl/cm2, the irradiated T. orientalis with 5.0 kGy, showed strong repellent activity against T. granarium larvae with the percentage repellency 100% (Class V) compared with the unirradiated oil (23.3 and 53.3%) after 2 h treatment. While at 0.252 μl/cm2, all three irradiated T. orientalis essential oil doses caused complete repellence for T. granarium larvae compared with the unirradiated oil (90%) after 2 h treatment. The present findings indicated that gamma radiation improves the insecticidal efficacy of T. orientalis essential oil and could be successfully used for the management of this insect pest.
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