Confirmation of Oryctes rhinoceros nudivirus infections in G-haplotype coconut rhinoceros beetles (Oryctes rhinoceros) from Palauan PCR-positive populations

Authors: TANAKA, SHUNSUKE - Tokyo University Of Agriculture & Technology; Harrison, Robert - Bob; HIROSHI, ARAI - Tokyo University Of Agriculture & Technology; KATAYAMA, YUKIE - Tokyo University Of Agriculture & Technology; MIZUTANI, TETSUYA - Tokyo University Of Agriculture & Technology; INOUE, MAKI - Tokyo University Of Agriculture & Technology; MILES, JOEL - Retired Non ARS Employee; MARSHALL, SEAN - Agresearch; KITALONG, CHRISTOPHER - Palau Community College; NAKAI, MADOKA - Tokyo University Of Agriculture & Technology

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2021
Publication Date: 9/20/2021
Citation: Tanaka, S., Harrison, R.L., Hiroshi, A., Katayama, Y., Mizutani, T., Inoue, M.N., Miles, J.E., Marshall, S.D., Kitalong, C., Nakai, M. 2021. Confirmation of Oryctes rhinoceros nudivirus infections in G-haplotype coconut rhinoceros beetles (Oryctes rhinoceros) from Palauan PCR-positive populations. Scientific Reports. https://doi.org/10.1038/s41598-021-97426-w.
DOI: https://doi.org/10.1038/s41598-021-97426-w

Interpretive Summary: The coconut rhinoceros beetle is an important insect pest of coconuts and other palm tree crops on islands in the Pacific Ocean. The use of chemical insecticides to kill this pest can have negative ecological, environmental, and health consequences. A naturally occurring insect virus has been used in the past to kill coconut rhinoceros beetles without the problems associated with chemical insecticides, but a new strain of this beetle has been identified that causes more palm damage and appears to be less susceptible to the virus. In this study, the prevalence of the beetle virus in adults of the new beetle strain in Palau was studied, and the infectivity and genome sequence of beetle virus from the new strain were determined and compared to the beetle virus stock that is normally used to kill the beetle. Virus was found in most of the adults from the new beetle strain. This virus was less infectious and exhibited genetic differences with the standard beetle virus stock. This information will be of interest to those in academia, government, and industry who work on coconut rhinoceros beetle and are trying to develop environmentally-friendly forms of insect control.

Technical Abstract: The coconut rhinoceros beetle (CRB), Oryctes rhinoceros, is a pest of palm trees in the Pacific. Recently, a remarkable degree of palm damage reported in Guam, Hawaii, Papua New Guinea and Solomon Islands has been associated with a particular haplotype (clade I), known as “CRB-G”, which can be distinguished by a molecular marker in the mitochondrial gene. In Palau Archipelago, it was reported that CRB-G and other haplotype (clade IV) belonging to the CRB-S cluster coexisted in the field. In this study, more than 75% of pheromone trap-captured adults of both of haplotypes were OrNV-positive by PCR. There was no significant difference in OrNV prevalence between the haplotypes. In tissues of PCR-positive CRB-G specimens from Palau, viral particles were observed by transmission electron microscopy. Hemocoel injection of CRB larvae with crude virus homogenates from these tissues resulted in viral infection and mortality. However, the OrNV isolates from Palauan beetles exhibited a lower level of viral production and longer larval survival times compared to OrNV isolate X2B, a typical isolate used for biological control of CRB in the Pacific. The full genome sequences of the Palauan and X2B isolates were determined and found to be closely related to each other. These results suggest that CRB adults in Palau are infected with a less virulent virus.