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Coconut rhinoceros beetle, Oryctes rhinoceros (L., 1758), is a large scarab beetle native to Southeast Asia and a major pest of coconut (Cocos nucifera) and oil (Elaeis guineensis) palms in its invaded range. Few tools are available for coconut rhinoceros beetle management, particularly for an emerging haplotype with resistance to known strains of Oryctes rhinoceros nudivirus, the traditional biological control agent used in coconut rhinoceros beetle management programs. RNA interference (RNAi) represents an emerging tool for insect pest control that exploits an existing pathway for gene regulation in the target organism. In this study, we evaluated RNAi as a potential tool for coconut rhinoceros beetle management. Using transcriptome data generated from gut tissue of early instar larvae, we identified 24 RNAi target sequences that were either highly expressed or had demonstrated efficacy in other insect systems. Double-stranded (ds)RNAs ranging from 249 to 297 bp in length were generated for 23 of these target sequences and 150 ng were microinjected into coconut rhinoceros beetle 1st, 2nd, and 3rd instar larvae and adults. Five of these dsRNAs that targeted genes putatively encoding V-type ATPase, polyadenylate binding protein, and three forms of actin induced 30.8–100% mortality within 14 days post injection (dpi). Microinjection of 2nd instars with 10 and 100 ng of these same five dsRNAs induced 20–100% and 80–100% mortality at 7 and 14 dpi, respectively. These results indicate RNAi should be explored as a possible management option for coconut rhinoceros beetle. Coconut rhinoceros beetle may also represent a model species for using RNAi in the management of large invasive insect species.

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Oryctes rhinoceros (Coleoptera: Scarabaeidae) is an invasive pest of palms in the Pacific Region, including Hawaii, for which limited management options are available. O. rhinoceros larvae develop in materials rich in organic materials such as green waste and animal manure. Biosolid waste within Hawaii’s infestation zone, however, was determined to inhospitable to O. rhinoceros. To determine if the elevated metal salts present in the biosolid waste was responsible for this observation, O. rhinoceros life stages were acutely and chronically exposed to several metal salts at increasing concentrations to determine the impact of these salts on survival, development, and oviposition behavior. Acute (7 days) exposure to mulch rehydrated in solutions of CaCl2, KCl, MgCl2, or NaCl increasing in concentration from 0 to 0.7 M resulted in increased mortality, with concentrations > 0.5 M generally being 100% lethal to both first and second-instar larvae. A similar trend in survival was observed in subsequent experiments using a horticultural grade of Epsom salt (MgSO4) at 1×, 2×, and 5× the recommended application rate. Chronic exposure (eggs reared on mulch through pupation) to Epsom salt at these same rates resulted in significantly delayed instar development and reduced adult biometrics at both 1× and 2× levels. Similar to the acute exposure, eggs exposed to 5× levels did not hatch, or the first instar died soon after emergence. In choice experiments, gravid females showed no oviposition preference for media hydrated with water or 2× Epsom salt but did avoid ovipositing in mulch rehydrated in 5× Epsom salt. These trials demonstrate a potentially novel approach to managing pest populations of O. rhinoceros.