Evaluations of local and commercial entomopathogenic fungal isolates as potential tools to manage Oryctes rhinoceros (Coleoptera: Scarabaeidae) in the Hawaiian Islands

Abstract

The coconut rhinoceros beetle, Oryctes rhinoceros (Linnaeus) (Coleoptera: Scarabaeidae), has re-emerged as a damaging and invasive insect pest of coconut palms and other palm species on the Pacific Islands. On the Hawaiian Island of O’ahu, populations were first detected in 2013. These were contained for 10 years through an extensive eradication program that utilized mass trapping, detector dogs, green waste sanitation, public outreach, and insecticidal treatments. Populations have since become widespread across the island and in 2023 localized O. rhinoceros populations were found on the islands of Maui, Kaua’i, and Hawai’i. We evaluated commercial and locally occurring entomopathogenic fungi to determine if these could be added to an integrated pest management program for long-term reduction of O. rhinoceros populations. Initial laboratory trials that screened locally collected isolates of Metarhizium anisopliae (Metschn.) Sorokīn (Hypocreales: Clavicipitaceae) found five isolates with greater than 60 % mortality on 1st instar larvae. These isolates were tested in comparison to a commercial entomopathogenic formulation of BotaniGard ES (Bioworks, Victor, New York; active ingredient Beauveria bassiana (Bals.-Criv.) Vuill.; Hypocreales: Cordycipitaceae), which caused greater than 60 % mortality at the high label application concentration. In semi field trials there was greater than 60 % mortality of 1st instar larvae when BotaniGard ES was applied as a mulch amendment. Further research is necessary to determine if there are methods to implement augmentative biological control through entomopathogenic fungi application into long term management for this damaging pest.