Dose response of coconut rhinoceros beetle (Coleoptera: Scarabaeidae) to 92 kV x-ray irradiation

Authors: JENKINS, DANIEL - University Of Hawaii; WATANABE, SHIZU - University Of Hawaii; Haff, Ronald - Ron; MELZER, MICHAEL - University Of Hawaii; Jackson, Eric; Liang, Peishih

Submitted to: Journal of Applied Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2021
Publication Date: 8/26/2021
Citation: Jenkins, D.M., Watanabe, S., Haff, R.P., Melzer, M.J., Jackson, E.S., Liang, P. 2021. Dose response of coconut rhinoceros beetle (Coleoptera: Scarabaeidae) to 92 kV x-ray irradiation. Journal of Applied Entomology. 145(10):1039-1049. https://doi.org/10.1111/jen.12930.
DOI: https://doi.org/10.1111/jen.12930

Interpretive Summary: The Coconut Rhinoceros Beetle (CRB) is an invasive beetle that is recently threatening coconut palm trees on the island of Oahu. Stakeholders are searching for methods to prevent the beetles spread beyond the limited known infestation sites with hopes of eradication. Sterile Insect Technique (SIT) is an insect control strategy in which large quantities of the target pest are sterilized and released to compete with the wild population. To determine the suitability of x-ray irradiation as a physical control method for CRB, either through SIT or through direct irradiation of naturally infested materials in the field, we conducted irradiation studies on all life stages of CRB using 92 keV x-rays. Eggs and larvae were highly susceptible to radiation at all tested doses, though adults required larger doses to render them incapable of reproducing. At exposures near 50 Gy sterilized adults nevertheless were observed to survive for more than a month, suggesting SIT may be a viable control approach for this beetle. Similarly these results may facilitate discovery of hidden breeding sites in the wild by tagging and releasing sterilized adults. While larvae were highly susceptible to x-ray irradiation, irradiation would probably not be an effective tool for field control due to rapid attenuation of radiation energy (exponential decay coefficients ranging from about 0.3 – 0.6 cm-1) in the organic nesting materials we tested, and the tendency for coconut rhinoceros beetle adults to burrow and oviposit deep in mulch (1 m or more).

Technical Abstract: To determine the potential suitability of x-ray irradiation as a physical control method for invasive Coconut Rhinoceros Beetle (Oryctes rhinoceros L., 1758), either through sterile insect technique (SIT) or through direct irradiation of naturally infested materials in the field, we conducted dosimetry studies on all life stages of coconut rhinoceros beetle using 92 keV x-rays. Eggs and larvae were highly susceptible to radiation at all tested doses (down to about 2 – 5 Gy), though adults required larger doses (at least 50 Gy) to render them incapable of reproducing. At exposures near 50 Gy sterilized adults nevertheless were observed to survive for more than a month, suggesting SIT may be a viable control approach for this beetle. Similarly these results may facilitate discovery of hidden breeding sites in the wild by tagging and releasing sterilized adults. While larvae were highly susceptible to x-ray irradiation, irradiation would probably not be an effective tool for field control due to rapid attenuation of radiation energy (exponential decay coefficients ranging from about 0.3 – 0.6 cm-1) in the organic nesting materials we tested, and the tendency for coconut rhinoceros beetle adults to burrow and oviposit deep in mulch (1 m or more).