Finding the next biological control agent for coconut rhinoceros beetle in the Pacific

A new haplotype (CRB Clade I) of coconut rhinoceros beetle, Oryctes rhinoceros, is invading the Pacific, threatening coconut and oil palm production. Historically, coconut rhinoceros beetle has been controlled successfully by its co-evolved pathogen, Oryctes rhinoceros nudivirus (OrNV), which was introduced to the Pacific in the late 1960s. However, these new invaders are resistant to the original biocontrol strain of OrNV and are causing intense damage to coconut palms in the affected countries. Screening new strains of OrNV against invasive CRB populations is a first step to finding a solution for this serious pest. Here we present results from bioassays conducted in the Solomon Islands and Papua New Guinea using two new OrNV strains: V23B and Dug42. Adult CRB were dosed orally with droplets of OrNV solution diluted with sugar water then kept individually for up to 6 weeks. Beetles in the control group were fed droplets of sugar water. All beetles were fed pieces of sugar cane and checked regularly, at least every 2-3 days. Deaths were recorded as they occurred and dead beetles dissected to collect gut samples. At the end of each bioassay, all surviving beetles were killed and dissected to collect gut samples. All gut samples were preserved for PCR analysis and histology to determine beetle haplotype and presence/absence of OrNV infection. Strain V23B showed strong virulence (50% mortality) against CRB from Guadalcanal but did not have the same impact on CRB from Port Moresby (0% mortality). Strain Dug42 showed some virulence (37% mortality) against CRB from Guadacanal and is being tested against CRB from Port Moresby. Implications from these bioassay results for biological control efforts against new CRB invasions are discussed.