The efficacy of the semiochemical repellent verbenone to reduce ambrosia beetle attack on healthy and Ceratocystis-infested ‘ohi'a trees

Authors: ROY, KYLLE - Us Forest Service (FS); Mikros, Dan; Cha, Dong; DUNKLE, ELLEN - University Of Hawaii; JUZWIK, JENNIFER - Us Forest Service (FS); GINZEL, MATTHEW - Purdue University

Submitted to: Forests, Trees and People
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/2024
Publication Date: 11/18/2024
Citation: Roy, K., Mikros, D.S., Cha, D.H., Dunkle, E.J., Juzwik, J., Ginzel, M. 2024. The efficacy of the semiochemical repellent verbenone to reduce ambrosia beetle attack on healthy and Ceratocystis-infested ‘ohi'a trees. Forests, Trees and People. 18. Article 100735. https://doi.org/10.1016/j.tfp.2024.100735.
DOI: https://doi.org/10.1016/j.tfp.2024.100735

Interpretive Summary: Fungal disease rapid ohia death (ROD) has killed over million ohia, the key stone tree species in Hawaii. The fungus can be spread by invasive ambrosia beetles that are attracted to ohia trees. Researchers at USDA-ARS, USDA-FS, USGS, University of Hawaii, and Purdue University have evaluated the effect of a known repellent, verbenone, as a method to protect ohia trees from ROD-associated ambroisa beetle attacks. Releasing verbenone around the bark of ohia trees at 1.3 m height resulted in significant reduction in beetle attacks compared to untreated trees, with a low dose of verbenone most effective on healthy ohia trees and a high dose most effective on diseased ohia. Our results suggest that verbenone may be an effective control approach to lower ambrosia beetle attack on ohia, thereby leading to reduction in the spread of ROD.

Technical Abstract: The Ceratocystis fungal disease complex, rapid 'ohi'a death (ROD), has killed over one million 'ohi'a (Metrosideros polymorpha), the keystone tree species of Hawai'i. The causal fungi can be spread by invasive ambrosia beetles (Coleoptera: Curculionidae) through fungal inoculum found on their bodies and also in the frass they produce. Thus, there is a critical need to manage beetle attack on 'ohi'a trees to curtail subsequent pathogen spread and disease development. In this experiment at Waiakea Forest Reserve, we tested the potential of the semiochemical repellent, verbenone, in commercial SPLAT® Verb formulation, to protect healthy and ROD-affected 'ohi'a from ambrosia beetle attack in each of the 2022 and 2023 field seasons. Landing rates of ambrosia beetles on healthy and diseased trees were quantified over 16-weeks in each year, using sticky traps on ethanol-baited trees that also received either a low (72 g) or high (108 g) dose of verbenone or untreated controls. In addition, we used gas-chromatography mass-spectrometry (GC-MS) to measure verbenone emission over 16 weeks in 2022. We found that the low dose of verbenone is the most effective and economical application to reduce beetle landing on healthy 'ohi'a trees and the high dose may be needed to reduce attraction to diseased 'ohi'a. Despite a large decrease in verbenone emission levels by week eight, the low dose effectively reduced beetle captures on healthy trees for 14 weeks and the high dose reduced landing rates on diseased trees for 10-14 weeks. Our results suggest verbenone may significantly lower ambrosia beetle attack on 'ohia, and thus, lead to reduction in the spread of ROD.