The use of chemical ecology for the management of ambrosia beetles in the rapid ʻŌhiʻa death pathosystem

Rapid ʻŌhiʻa Death (ROD) is a fungal disease complex that can be vectored by invasive ambrosia beetles (Colepotera: Curculionidae) through direct contact or through the spread of infested frass particles. ROD is caused by two Ceratocystis fungi, C. lukuohia and C. huliohia, and it is killing the keystone tree species of Hawaiʻi, ʻōhiʻa lehua (Metrosideros polymorpha). The four invasive ambrosia beetle vectors include Xyleborinus saxesenii, Xyleborus affinis, Xyleborus bispinatus, and Xyleborus perforans, and disentangling the contribution of each species to disease spread is vital to management. I will discuss the use of semiochemical attractants and repellents for manipulating ambrosia beetles and identifying the volatiles produced in the pathosystem and the attraction of ambrosia beetles to those volatiles. Our work has found that ethanol is the preferred beetle attractant, and both SPLAT Verb and SPLAT Beetle Guard are effective repellents to deter beetle attack from both standing and felled ʻōhiʻa trees. The ROD pathogens produce fruity volatiles that attract X. affinis, X. bispinatus, and X. perforans, and may repel Xi. saxesenii. Infected ʻōhiʻa seedlings produce key defense compounds such as methyl salicylate and limonene. Early detection of stress and fungal volatiles in seedling prior to symptom onset is possible, although application to field trees requires testing. The use of chemical ecology in the ROD pathosystem has led to important discoveries but further work is needed to improve integrated pest management plans.