Presence and viability of Ceratocystis lukuohia in ambrosia beetle frass from Rapid ʻŌhiʻa Death‐affected Metrosideros polymorpha trees on Hawaiʻi Island

Abstract

AbstractRapid ʻŌhiʻa Death (ROD) is a fungal disease of ʻōhiʻa lehua (Myrtaceae: Metrosideros polymorpha) caused by Ceratocystis lukuohia and C. huliohia. ROD is the aetiological agent of widespread mortality of this important tree on Hawaiʻi Island, but its epidemiology remains unclear. We investigated the prevalence and viability of C. lukuohia in ambrosia beetle frass in ROD‐affected ʻōhiʻa trees. A total of 200 frass traps were placed onto C. lukuohia‐infected ʻōhiʻa at four locations on the east side of Hawaiʻi Island. Frass was collected and screened for the presence of C. lukuohia DNA using a diagnostic qPCR assay. In addition, frass samples were screened for viability by carrot baiting. All trapped beetles were of the genus Xyleborus, with the majority being the non‐native X. ferrugineus. Of the frass samples tested, 62% contained C. lukuohia DNA and 17% of carrot baits were positive for the fungus. These results indicate that ambrosia beetle frass releases C. lukuohia into the environment. We discuss the potential role infested frass could play in the ROD pathosystem.