Coconut rhinoceros beetle in Solomon Islands: a tale of two invasions

The coconut rhinoceros beetle (CRB) (Oryctes rhinoceros) was accidentally introduced into Samoa with planting material more than a century ago. During the last century, CRB has spread to several other Pacific and Indian Ocean islands and is considered to be a major pest of coconut and other palms. In 2015 CRB was discovered in a small outbreak in Honiara, Guadalcanal, Solomon Islands. This was the first record of CRB from Solomon Islands. Following delimitation surveys and a public awareness programme CRB presence was confirmed beyond Honiara. Later in 2015, CRB was also reported from the Shortland Islands in the Western Province with other islands surveyed from 2015 to 2020. Where CRB presence was confirmed, beetles were collected and analysed for haplotype and presence of the classical biological control agent, Oryctes rhinoceros nudivirus (OrNV) with a distribution map and timeline of invasion subsequently developed. The initial populations belonged to two distinct variants: CRB-G (clade IA) in Honiara and CRB-S (clade II) in Shortland Islands; no OrNV was originally detected in either population. Despite control efforts, by 2020 CRB-G had spread to islands in eight provinces and CRB-S had spread to islands in seven provinces. Additionally, CRB-S and CRB-G have been found to co-occur on several islands. In 2019, OrNV was detected from field collected CRB from Guadalcanal and has since spread to Malaita Island. In both cases the virus was detected where CRB-G and CRB-S cooccur. The two haplotypes appear to have spread following patterns of air and sea movement between the point of origin (CRB-G from Honiara and CRB-S from the Shortland Islands) to other islands/provinces. The monitoring of CRB dispersal, coupled with local observations during field surveys, has allowed tracking of invasion pathways and allowed biosecurity measures and pest management recommendations to be tailored to specific outbreaks.