Comparing the biological effectiveness of low energy 100 kV and high energy 5 MeV X-rays against Oriental fruit fly (Diptera: Tephritidae)

Authors: Follett, Peter; FEZZA, T. - Animal And Plant Health Inspection Service (APHIS); Ladizinsky, Nicolas; Liang, Peishih

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/16/2024
Publication Date: 8/2/2024
Citation: Follett, P.A., Fezza, T.J., Ladizinsky, N.C., Liang, P. 2024. Comparing the biological effectiveness of low energy 100 kV and high energy 5 MeV X-rays against Oriental fruit fly (Diptera: Tephritidae). Journal of Economic Entomology. 117(5):1815-1822. https://doi.org/10.1093/jee/toae169.
DOI: https://doi.org/10.1093/jee/toae169

Interpretive Summary: Irradiators with radioactive isotope sources such as Cesium-137 and Cobalt-60 are commonly used for phytosanitary irradiation to control insects in exported fruit and for sterile insect release programs to sterilize insects. Since 9/11, there are institutional initiatives to replace isotope sources with lower-energy X-ray sources due to concerns about radiological terrorism. High energy X-ray irradiators are generally thought to be the same as isotope irradiators such as Cobalt-60, and Hawaii has a commercial high energy x-ray facility that treats fruit for export. But there is also interest in using lower energy systems for various purposes. The question arises whether the biological effectiveness of x-rays at different energies and dose rates is the same as for isotopic irradiators, e.g., cobbalt-60. We showed that 100 kV x-rays (low energy) were more effective than 5 MeV x-rays (high energy) against Oriental fruit fly. It is important that research to develop phytosanitary irradiation treatments that may become internationally approved protocols and widely used commercially provide reliable and repeatable efficacy. The relative biological effectiveness of irradiation using low energy X-rays may be machine energy level and dose rate dependent and therefore x-ray energies around 100 kV should not be used to develop regulatory phytosanitary irradiation treatments.

Technical Abstract: Radionuclide irradiators (137Cs and 60Co) are commonly used for phytosanitary irradiation to control insects in exported fruit and for sterile insect release programs to sterilize insects. There are institutional initiatives to replace radionuclide sources with lower-energy X-ray sources due to concerns about radiological terrorism. Questions remain about whether the biological effects of low-energy X-rays are comparable to Y-rays since different energies and dose rates may cause different effects. We compared adult emergence and performance in Oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritdae), after irradiation of third instar larvae with 100 kV or 5 MeV X-rays at 20 and 40 Gy in replicated studies. At 20 Gy, adult emergence rate was significantly lower after irradiation with 100 kV compared to 5 MeV X-rays, indicating higher efficacy at the lower energy. In a follow-up study, a comparison was made between a slow (0.24 Gy min-1) and fast (3.3 Gy min-1) dose rate using 100 kV x-rays. The slow dose rate showed significantly higher adult emergence than the fast dose rate, indicating lower efficacy, but flight ability was poor in both treatments. The relative biological effectiveness of irradiation using low energy X-rays may be machine energy level and dose rate dependent and therefore x-ray energies around 100 kV should not be used to develop regulatory phytosanitary irradiation treatments.