Basil oil fumigation increases radiation sensitivity in adult Sitophilus oryzae (Coleoptera: Curculionidae)

The biological activity of basil (Ocimum basilicum L.) oil vapor was tested against the stored product pest rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae). Adult weevils were exposed to seven different concentrations of basil oil ranging from 0.12 μl/ml-0.60 μl/ml in Petri dishes and mortality was assessed at 3, 4 and 5 d post treatment. Mortality increased with increasing exposure time and basil oil concentration. At 3, 4 and 5 d post treatment, the LC50 values were 8.14, 6.50 and 4.91 μl/ml of basil oil, respectively. S. oryzae was also exposed to 0.12 or 0.24 μl/ml basil oil and irradiated at 20, 40, 60, 80, 100 or 120 Gy in Petri dishes before mortality assessment at 5 d post treatment. The effectiveness of irradiation treatment against S. oryzae was enhanced by exposure to basil oil. S. oryzae exposed to 0.12 and 0.24 μl/ml of basil oil were 4.1 and 5.3 times more sensitive to irradiation, respectively, compared to control weevils treated only with irradiation. The effect of basil oil and irradiation on mortality was synergistic when used in combination against S. oryzae in packaged rice. The type of rice package affected treatment efficacy. In paper rice packages, 78% mortality was observed with 2.5 μl/ml basil oil and a radiation dose of 200 Gy at 5 d post treatment. In plastic packages, 100% mortality was achieved with 0.83 μl/ml basil oil and a radiation dose of 200 Gy at 5 d post treatment. Basil oil has potential as a synergist to lower the radiation dose required to control phytosanitary pests.