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

Shunsuke Tanaka,Sean D G Marshall,Robert L Harrison,Yukie Katayama,Hiroshi Arai,Joel Miles,Tetsuya Mizutani,Madoka Nakai,Maki N Inoue,Christopher Kitalong

doi:10.1038/s41598-021-97426-w

Abstract

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”. In the Palau Archipelago, both CRB-G and another haplotype (clade IV) belonging to the CRB-S cluster coexist in the field. In this study, more than 75% of pheromone trap-captured adults of both haplotypes were Oryctes rhinoceros nudivirus (OrNV)-positive by PCR. No significant difference in OrNV prevalence between the haplotypes was detected. In PCR-positive CRB-G tissue specimens from Palau, viral particles were observed by electron microscopy. Hemocoel injection of CRB larvae with crude virus homogenates from these tissues resulted in viral infection and mortality. OrNV isolated from Palauan-sourced CRB was designated as OrNV-Palau1. Both OrNV-Palau1 and OrNV-X2B, a CRB biological control isolate released in the Pacific, were propagated using the FRI-AnCu-35 cell line for production of inoculum. However, the OrNV-Palau1 isolate exhibited lower viral production levels and longer larval survival times compared to OrNV-X2B in O. rhinoceros larvae. Full genome sequences of the OrNV-Palau1 and -X2B isolates were determined and found to be closely related to each other. Altogether these results suggest CRB adults in Palau are infected with a less virulent virus, which may affect the nature and extent of OrNV-induced pathology in Palauan populations of CRB.

Highlights

Coconut palms, often referred to as the “tree of life”[1] in the Pacific, provide numerous benefits to human society
There was no significant difference between the prevalence of Oryctes rhinoceros nudivirus (OrNV) in Coconut rhinoceros beetle (CRB)-G and CRB-S (χ2 test, χ2 = 0.191, p = 0.662)
A majority of the field-captured O. rhinoceros adults (60%) were CRB-G, and 77.5% of both haplotypes were OrNV-positive by PCR detection (Table 1) in Palau, which is consistent with a previous r eport[9]

Summary

Introduction

Often referred to as the “tree of life”[1] in the Pacific, provide numerous benefits to human society. As the meristem of palm is in the crown, burrowing activity commonly damages developing palm fronds, which generally display a characteristic “V-shaped” notching pattern once unfurled. This feeding action leads to reductions in both coconut palm growth and nut production due to a reduction of photosynthesis efficiency, and can cause death if the meristem itself is d amaged[2]. In the Palau archipelago of Micronesia, the population of CRB is a distinctive mixture of both CRB-G and CRB-S adults analyzed by P CR9 This implies that the new CRB-G haplotype can invade other countries and regions occupied by other CRB haplotypes.

Methods

Results

Conclusion