Temporal associations between ambrosia beetles and ʻōhiʻa ( <i>Metrosideros polymorpha</i> ) artificially inoculated with <i>Ceratocystis lukuohia</i>

Abstract Wood boring ambrosia beetles play a central role in the spread of Ceratocystis wilt of ‘ōhi‘a, a fungal disease caused by Ceratocystis lukuohia that kills the bioculturally important ‘ōhiʻa ( Metrosideros polymorpha ) tree. Beetles contribute to the spread of the disease by extruding fungus‐infected wood particles (frass). Disease mitigation can benefit from knowledge of ambrosia beetle life‐history and fungal survival in affected ‘ōhi‘a. We investigated temporal associations among tree death, the timing and duration of beetle attacks, and the persistence of viable C. lukuohia within intentionally infected (inoculated) ʻōhiʻa at three sites that approximate the elevational range of the disease on the Island of Hawaiʻi. Beetles most frequently attacked inoculated trees at the time when foliage first showed symptoms of infection (yellow leaves; n = 9) although some attacks were observed during earlier (green leaf; n = 3) and later (brown leaf; n = 3) stages of symptom progression. On average, beetles initiated new attacks for nearly one year after trees were inoculated. We tracked active galleries of Xyleborinus saxesenii , Xyleborus ferrugineus and Xyleborus simillimus and found they produced frass with viable C. lukuohia propagules for 122.8 ± 40.0, 275.8 ± 32.7 and 304.2 ± 53.4 days, respectively. Infected ʻōhiʻa felled from our mid‐elevation site at the end of the study revealed viable fungal propagules and the presence of X. ferrugineus over two years after trees first appeared symptomatic of infection, suggesting that Ceratocystis wilt of ʻōhiʻa remains a threat to spread from infected trees long after trees succumb to the disease.