X-ray based sterilization of larvae of the navel orangeworm (lepidoptera:pyralaide) for sterile insect technique

Authors: Haff, Ronald - Ron; Ovchinnikova, Inna; Liang, Peishih; Mahoney, Noreen; Gee, Wai; Gomez, Joseph - Jose; Toyofuku, Natsuko; Jackson, Eric; Hnasko, Robert; LIGHT, DOUGLAS - Former ARS Employee

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2020
Publication Date: 6/20/2020
Citation: Haff, R.P., Ovchinnikova, I., Liang, P., Mahoney, N.E., Gee, W.S., Gomez, J., Toyofuku, N., Jackson, E.S., Hnasko, R.M., Light, D. 2020. X-ray based sterilization of larvae of the navel orangeworm (lepidoptera:pyralaide) for sterile insect technique. Journal of Economic Entomology. 113(4):1685-1693. https://doi.org/10.1093/jee/toaa111.
DOI: https://doi.org/10.1093/jee/toaa111

Interpretive Summary: Sterile Insect Technique (SIT) is a pest control strategy in which insects are produced in large numbers, sterilized by irradiation, then released in the wild to compete with the indigenous population. The suitability of adult male Navel orangeworm (NOW) for use in SIT has been established for both high energy gamma and low energy x-ray sterilization. In either case the units in which irradiation dose is measured are the same, with the unit of measurement being Grays (Gy). However, research regarding sterilization of NOW larvae by gamma irradiation indicated non-suitability due to high mortality. Here, NOW larvae were irradiated with x-rays and results compared to those for gamma irradiation. Small and medium sized larvae were irradiated to doses up to 50 Gy then paired with non-irradiated colony mates and observed for mortality, then for the sterility of surviving insects as determined by the presence or absence of fertilized eggs. Small larvae experienced 77% mortality at a dose of 30 Gy, vs. 20% for non-irradiated control. At 40 Gy, mortality reached 98%. Of surviving small larvae at 30 Gy, 29% of insect pairs produced fertilized eggs. While presence of red eggs does not guarantee viability, the absence does guarantee infertility (as is appropriate for SIT) and was thus the measure used here. For large larvae, no red eggs were produced at 40 Gy, but mortality was 73%. These results are consistent with reported results for gamma irradiation of NOW larvae where sterility was observed somewhere between the 30 Gy and 60 Gy data points, but mortality was high. This confirms the lack of suitability of NOW irradiated in the larval stage, whether by gamma or x-ray, and supports the hypothesis that x-ray and gamma treatments are biologically equivalent at equal doses.

Technical Abstract: The suitability of adult male Navel orangeworm (NOW), Amyelois transitella (Walker) for use in Sterile Insect Technique (SIT) has been established for both high energy gamma (>1MeV) and low energy x-ray (90 keV) sterilization. However, research regarding sterilization of NOW larvae by gamma irradiation indicated non-suitability due to high mortality. Here, NOW larvae were irradiated with 90 keV x-rays and results compared to those for gamma irradiation. Small and medium sized larvae were irradiated to doses up to 50 Gy then paired with non-irradiated colony mates and observed for mortality, then for the sterility of surviving insects as determined by the presence or absence of fertilized eggs. Small larvae experienced 77% mortality at a dose of 30 Gy, vs. 20% for non-irradiated control. At 40 Gy, mortality reached 98%. Of surviving small larvae at 30 Gy, 29% of insect pairs produced fertilized eggs. While presence of red eggs does not guarantee viability, the absence does guarantee infertility (as is appropriate for SIT) and was thus the measure used here. For large larvae, no red eggs were produced at 40 Gy, but mortality was 73%. These results are consistent with reported results for gamma irradiation of NOW larvae where sterility was observed somewhere between the 30 Gy and 60 Gy data points, but mortality was high. This confirms the lack of suitability of NOW irradiated in the larval stage, whether by gamma or x-ray, and supports the hypothesis that x-ray and gamma treatments are biologically equivalent at equal doses.