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

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.

Diverse Host Immune Responses of Different Geographical Populations of the Coconut Rhinoceros Beetle to Oryctes Rhinoceros Nudivirus (OrNV) Infection

“…Resistance to OrNV in the CRB-G mitochondrial lineage has been proposed because of an absence of OrNV infection in wild-caught insects from this haplotype group and the results from laboratory bioassays investigating the susceptibility of adult O. rhinoceros from the Guam population of this lineage to orally administered OrNV ( 2 ). However, our recent studies demonstrate the high incidence of virus in wild-caught O. rhinoceros across the region regardless of their mitochondrial lineage ( 1 ) and detection of OrNV in the CRB-G mitochondrial lineage in the Solomon Islands ( 6 ), the Philippines ( 7 ), and Palau ( 8 ). Interestingly, harmonious topologies of both host and OrNV strains provide evidence of codivergence of OrNV strains with their O. rhinoceros hosts across the Pacific ( 7 ).…”