BACKGROUND The fungi, Metarhizium spp., are well known as pathogens of CRB (Oryctes rhinoceros), but natural infection in the field is relatively low. Infection levels can be increased by the application of laboratory- produced Metarhizium spores into breeding sites. Artificial breeding sites (ABS) can be constructed from decomposing palm logs and associated plant waste and treated with fungus. Female CRB are attracted to the decomposing material to lay eggs, commercial aggregation pheromones can be used to increase attraction. Immature stages of CRB will become infected and die, but infected emerging adults will spread the fungus. In this study, a locally isolated strain of Metarhizium majus was tested by applying to ABS. The impact of the application on CRB population and fungus dispersal was determined. METHODS • Isolate F717 (S4) isolated from one adult CRB cadaver found in an oil palm plantation at Tetere, Guadalcanal. • Conidia production Conidia were produced on rice grains (Figure 1) using solid fermentation (Nelson and Glare 1996). • Field trial M. majus was tested by applying nil, low (100g/ABS), moderate (200g/ABS) and high (400g/ABS) doses of sporulated rice (Figure 1) to four 2 x 2m ABS arranged in a grid (Figure 2). 50 CRB larvae were added to each ABS. This design was repeated at three oil palm blocks in Guadalcanal (Solomon Islands): Tetere, Mberande and Nekama. CRB numbers (adults and larvae) inside the ABS were assessed every 2 months for 6 months. Before applying the fungus, soil samples were taken at 10m, 50m and 100m from each ABS. The soil samples were ‘baited' with CRB larvae to detect Metarhizium sp. Soil baiting was repeated at 2-monthly intervals. DISCUSSION Results showed that isolate F717 (S4) is pathogenic to CRB larvae and adults in the ABS. Soil baiting showed that M. majus spread up to 100m from treated ABS and persist for at least 6 months at some sites. M. majus may contribute to CRB control if high levels of inoculum can persist in breeding sites under field conditions. Paul Gende1, Simon Chris1, Sean Marshall2, Sarah Mansfield2, Trevor Jackson2, Laura Villamizar 2 1Papua New Guinea Oil Palm Research Association, New Britain Palm Oil, Guadalcanal Plains, Honiara, Solomon Islands 2AgResearch Ltd. Lincoln Research Centre, Christchurch, New Zealand Address for correspondence: laura.villamizar@agresearch.co.nz Performance of Metarhizium majus applied in artificial breeding sites to control larvae of coconut rhinoceros beetle (CRB) in Solomon Islands Metarhizium majus applied as sporulated rice in artificial breeding sites can spread from the treated area and persist in the field for up to 6 months RESULTS Less than 32 CRB larvae/ABS were found during the 2-monthly evaluations at Tetere and Mberande. At Nekama, between 48 and 62 CRB larvae were found in the ABS from the control treatment after 2 and 6 months while less than 35 CRB larvae were found in fungus- applied ABS at all evaluation times. CRB cadavers showing green sporulation consistent with infection by M. majus were found inside ABS and pheromone traps. Metarhizium sp. was detected in Tetere soil samples from all distances/treatments before and after the inoculation of the ABS (Figure 3), suggesting the fungus was already established in this block after a commercial product with M. majus was applied in 2017. In contrast, Metarhizium sp. was not detected in soil samples collected from Mberande and Nekama before ABS inoculation, but the fungus was detected later in soil samples from all treatments, even at 100m away from the site. Figure 1. CRB larva infected with M. majus (A), M. majus grown on agar (B) and rice (C) A A B C Figure 3. Detection of M. majus spread from the ABS using the soil baiting method Control Low rate Medium rate High rate Figure 2. Experimental plot design for assessment of M. majus performance in ABS under field conditions Artificial Breeding Sites (ABS) Pheromone traps Sampling points