Targeting Infection at the Source: evaluating the efficacy of semiochemical repellent compounds in the management of rapid ʻōhiʻa death-associated ambrosia beetles













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Rapid ʻōhiʻa death (ROD) is a highly virulent and aggressive fungal disease that has been devastating ʻōhiʻa forests on Hawai‘i Island since the mid 2010s. ʻŌhiʻa (Metrosideros polymorpha) is the dominant keystone tree species in native Hawaiian wet forests and its decimation could lead to an ecological collapse. . Therefore, management strategies for preventing ROD transmission are crucial. Ambrosia beetles have been implicated as the primary dissemination agents of environmental inoculum and have the capacity to directly transmit the pathogens as well. Currently, the only widely endorsed management recommendation is to fell and tarp infected trees, thereby physically isolating beetles and inoculum from the environment. But this is often neither practical nor does it offer a preventative strategy for inoculum production. Alternatively, non-toxic semiochemical repellents, which exploit the beetles’ chemical communication system, have been shown to be effective against similar ambrosia beetle species, and may be useful in regards to ROD. I tested the efficacy of two semiochemical repellents, SPLAT Verb® (10% verbenone) and SPLAT Beetle Guard® (10% verbenone + 10% methyl salicylate) for their ability to reduce beetle attack, colonization, and frass production when applied to felled ROD-Ceratocystis infested ʻōhiʻa wood in order to examine the products’ utility as an alternative post-felling management solution. Verbenone alone displayed the capacity to reduce new beetle gallery formations and frass production, but not beetle emergence. Verbenone + MeSA also exhibited the ability to reduce galleries, more so than verbenone in one of the trials, and reduced beetle emergence and frass production. As beetle attack and frass production are the primary concern to inoculum dissemination, both products show a strong potential for use as an active ROD management treatment. After felling trees, new beetle attacks subsided to near zero across all treatments by week 10 in both trials, suggesting a single application of repellent is suitable to protect target trees for the extent of their host-suitability period post-felling. Semiochemical beetle repellents will play a pivotal role in the multifaceted management approach that is needed to manage the disease, and the findings from this project support the growing body of evidence surrounding their use within the ROD pathosystem. Due to the products’ accessibility and ease of use, they offer a comparatively simple management strategy which can be widely employed by land managers and the general public to reduce infectious material in the environment and restrict ROD transmission.



Entomology, Wildlife management, Conservation biology, Ambrosia Beetle, Ceratocystis, Forest Management, Forest Pathogen, Rapid ʻŌhiʻa Death, Semiochemical



43 pages


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