Radiosensitization of rice weevil Sitophilus oryzae using combined treatments of essential oils and ionizing radiation with gamma-ray and X-Ray at different dose rates

Authors: HOSSAIN, F - Institut National De La Recherche Scientifique (INRS); Follett, Peter; SHANKAR, S - Institut National De La Recherche Scientifique (INRS); BEGUM, T - Institut National De La Recherche Scientifique (INRS); SALMIERI, S - Institut National De La Recherche Scientifique (INRS); LACROIX, M - Institut National De La Recherche Scientifique (INRS)

Submitted to: Radiation Physics and Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2020
Publication Date: 11/20/2020
Citation: Hossain, F., Follett, P.A., Shankar, S., Begum, T., Salmieri, S., Lacroix, M. 2020. Radiosensitization of rice weevil Sitophilus oryzae using combined treatments of essential oils and ionizing radiation with gamma-ray and X-Ray at different dose rates. Journal of Radiation Physics and Chemistry. 180. Article 109286. https://doi.org/10.1016/j.radphyschem.2020.109286.
DOI: https://doi.org/10.1016/j.radphyschem.2020.109286

Interpretive Summary: The stored grain pest rice weevil, Sitophilus oryzae, received a combination disinfestation treatment of eucalyptus essential oil or tea tree essential oil and irradiation by gamma or x-ray source at different dose rates in rice. Irradiation at sublethal doses greatly enhanced the fumigation toxicity of the plant essential oils. Gamma irradiation at high dose rates appeared to have greater synergistic effects than gamma irradiation at a lower dose rate and x-ray irradiation. Plant essentail oils such as eucalyptus and tea tree are highly toxic to rice weevil, with or without irradiation, and may provide an alternative for control of stored product pests to standard fumigation with methyl bromide or phosphine.

Technical Abstract: Stored product pests such as the rice weevil, Sitophilus oryzae (Coleoptera: Curculionidae) can be controlled in bulk and packaged grains by ionizing radiation ('-radiation or X-ray radiation) and plant essential oils, used in combination or alone, as an alternative to standard chemical fumigantion. Irradiation source and dose rate may be a factor in enhancing the effect of plant essential oils. The effects of '-radiation at three dose rates (10.445, 4.558, and 0.085 kGy/h) and X-ray irradiation at two dose rates (0.76 and 0.19 kGy/h) in combination with Tea tree (Melaleuca alternifolia) and Eucalyptus (Eucalyptus globules) essential oils (EOs) on the short-term mortality of S. oryzae was evaluated. Adult weevils on rice in Petri dishes were fumigated with 10 µL/mL EOs and then irradiated with a dose of 100, 250, 500, or 750 Gy. The results showed that the combined treatment of Eucalyptus or Tea tree EOs with '-irradiation or x-ray irradiation increased the mortality by 3–6 times as compared to irradiation treatment alone. The LD90 values for Eucalyptus EO plus ' irradiation treated samples were 250.6, 252.8, and 522.4 Gy at dose rates of 10.445, 4.558, and 0.085 kGy/h, respectively, whereas the LD90 values for Tea tree EO plus '-irradiation were similar at 250.1, 255.07, and 574.3 Gy dose rates, respectively. The lowest dose rate of '-irradiation had the lowest efficacy in the combination treatment for both EOs. For the combined treatment of Eucalyptus or Tea tree EO with X-ray irradiation, LD90 values were 746.02 and 737.1 Gy with Eucalyptus EO and 632.03 and 615.5 Gy with Tea tree EO, at dose rates of 0.76 and 0.19 kGy/h, respectively. Overall, combination treatment LD90 values were significantly higher (p < 0.05) (less effective treatment) for x-ray than for '-ray irradiation. Unlike '-irradiation, the dose rate of X-ray irradiation did not affect efficacy in the combined treatments. Gamma or low energy X-ray irradiation and plant EOs such as Eucalyptus or Tea tree EOs applied alone or in combination, are effective insecticidal treatments. However, our results suggested that synergistic effects with EOs against S. oryzae in rice may be higher (lower LD90 values) for '-radiation than X-ray treated insects.